Distributed Multihead X design

Kevin E. Martin

David H. Dawes

Rickard E. Faith

29 June 2004 (created 25 July 2001)

This document covers the motivation, background, design, and implementation of
the distributed multihead X (DMX) system. It is a living document and describes
the current design and implementation details of the DMX system. As the project
progresses, this document will be continually updated to reflect the changes in
the code and/or design. Copyright 2001 by VA Linux Systems, Inc., Fremont,
California. Copyright 2001-2004 by Red Hat, Inc., Raleigh, North Carolina

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Table of Contents

Introduction

    The Distributed Multihead X Server
    Layout of Paper

Development plan

    Bootstrap code
    Input device handling
    Output device handling
    Optimizing DMX
    DMX X extension support
    Common X extension support
    OpenGL support

Current issues

    Fonts
    Zero width rendering primitives
    Output scaling
    Per-screen colormaps

A. Appendix

    Background

        Core input device handling
        Output handling
        Xinerama

    Development Results

        Phase I
        Phase II
        Phase III
        Phase IV

Introduction

The Distributed Multihead X Server

Current Open Source multihead solutions are limited to a single physical
machine. A single X server controls multiple display devices, which can be
arranged as independent heads or unified into a single desktop (with Xinerama).
These solutions are limited to the number of physical devices that can co-exist
in a single machine (e.g., due to the number of AGP/PCI slots available for
graphics cards). Thus, large tiled displays are not currently possible. The
work described in this paper will eliminate the requirement that the display
devices reside in the same physical machine. This will be accomplished by
developing a front-end proxy X server that will control multiple back-end X
servers that make up the large display.

The overall structure of the distributed multihead X (DMX) project is as
follows: A single front-end X server will act as a proxy to a set of back-end X
servers, which handle all of the visible rendering. X clients will connect to
the front-end server just as they normally would to a regular X server. The
front-end server will present an abstracted view to the client of a single
large display. This will ensure that all standard X clients will continue to
operate without modification (limited, as always, by the visuals and extensions
provided by the X server). Clients that are DMX-aware will be able to use an
extension to obtain information about the back-end servers (e.g., for placement
of pop-up windows, window alignments by the window manager, etc.).

The architecture of the DMX server is divided into two main sections: input
(e.g., mouse and keyboard events) and output (e.g., rendering and windowing
requests). Each of these are describe briefly below, and the rest of this
design document will describe them in greater detail.

The DMX server can receive input from three general types of input devices:
"local" devices that are physically attached to the machine on which DMX is
running, "backend" devices that are physically attached to one or more of the
back-end X servers (and that generate events via the X protocol stream from the
backend), and "console" devices that can be abstracted from any non-back-end X
server. Backend and console devices are treated differently because the pointer
device on the back-end X server also controls the location of the hardware X
cursor. Full support for XInput extension devices is provided.

Rendering requests will be accepted by the front-end server; however, rendering
to visible windows will be broken down as needed and sent to the appropriate
back-end server(s) via X11 library calls for actual rendering. The basic
framework will follow a Xnest-style approach. GC state will be managed in the
front-end server and sent to the appropriate back-end server(s) as required.
Pixmap rendering will (at least initially) be handled by the front-end X
server. Windowing requests (e.g., ordering, mapping, moving, etc.) will handled
in the front-end server. If the request requires a visible change, the
windowing operation will be translated into requests for the appropriate
back-end server(s). Window state will be mirrored in the back-end server(s) as
needed.

Layout of Paper

The next section describes the general development plan that was actually used
for implementation. The final section discusses outstanding issues at the
conclusion of development. The first appendix provides low-level technical
detail that may be of interest to those intimately familiar with the X server
architecture. The final appendix describes the four phases of development that
were performed during the first two years of development.

The final year of work was divided into 9 tasks that are not described in
specific sections of this document. The major tasks during that time were the
enhancement of the reconfiguration ability added in Phase IV, addition of
support for a dynamic number of back-end displays (instead of a hard-coded
limit), and the support for back-end display and input removal and addition.
This work is mentioned in this paper, but is not covered in detail.

Development plan

This section describes the development plan from approximately June 2001
through July 2003.

Bootstrap code

To allow for rapid development of the DMX server by multiple developers during
the first development stage, the problem will be broken down into three tasks:
the overall DMX framework, back-end rendering services and input device
handling services. However, before the work begins on these tasks, a simple
framework that each developer could use was implemented to bootstrap the
development effort. This framework renders to a single back-end server and
provides dummy input devices (i.e., the keyboard and mouse). The simple
back-end rendering service was implemented using the shadow framebuffer support
currently available in the XFree86 environment.

Using this bootstrapping framework, each developer has been able to work on
each of the tasks listed above independently as follows: the framework will be
extended to handle arbitrary back-end server configurations; the back-end
rendering services will be transitioned to the more efficient Xnest-style
implementation; and, an input device framework to handle various input devices
via the input extension will be developed.

Status: The boot strap code is complete.

Input device handling

An X server (including the front-end X server) requires two core input devices
-- a keyboard and a pointer (mouse). These core devices are handled and
required by the core X11 protocol. Additional types of input devices may be
attached and utilized via the XInput extension. These are usually referred to
as ``XInput extension devices'',

There are some options as to how the front-end X server gets its core input
devices:

 1. Local Input. The physical input devices (e.g., keyboard and mouse) can be
    attached directly to the front-end X server. In this case, the keyboard and
    mouse on the machine running the front-end X server will be used. The
    front-end will have drivers to read the raw input from those devices and
    convert it into the required X input events (e.g., key press/release,
    pointer button press/release, pointer motion). The front-end keyboard
    driver will keep track of keyboard properties such as key and modifier
    mappings, autorepeat state, keyboard sound and led state. Similarly the
    front-end pointer driver will keep track if pointer properties such as the
    button mapping and movement acceleration parameters. With this option,
    input is handled fully in the front-end X server, and the back-end X
    servers are used in a display-only mode. This option was implemented and
    works for a limited number of Linux-specific devices. Adding additional
    local input devices for other architectures is expected to be relatively
    simple.

    The following options are available for implementing local input devices:

     a. The XFree86 X server has modular input drivers that could be adapted
        for this purpose. The mouse driver supports a wide range of mouse types
        and interfaces, as well as a range of Operating System platforms. The
        keyboard driver in XFree86 is not currently as modular as the mouse
        driver, but could be made so. The XFree86 X server also has a range of
        other input drivers for extended input devices such as tablets and
        touch screens. Unfortunately, the XFree86 drivers are generally
        complex, often simultaneously providing support for multiple devices
        across multiple architectures; and rely so heavily on XFree86-specific
        helper-functions, that this option was not pursued.

     b. The kdrive X server in XFree86 has built-in drivers that support PS/2
        mice and keyboard under Linux. The mouse driver can indirectly handle
        other mouse types if the Linux utility gpm is used as to translate the
        native mouse protocol into PS/2 mouse format. These drivers could be
        adapted and built in to the front-end X server if this range of
        hardware and OS support is sufficient. While much simpler than the
        XFree86 drivers, the kdrive drivers were not used for the DMX
        implementation.

     c. Reimplementation of keyboard and mouse drivers from scratch for the DMX
        framework. Because keyboard and mouse drivers are relatively trivial to
        implement, this pathway was selected. Other drivers in the X source
        tree were referenced, and significant contributions from other drivers
        are noted in the DMX source code.

 2. Backend Input. The front-end can make use of the core input devices
    attached to one or more of the back-end X servers. Core input events from
    multiple back-ends are merged into a single input event stream. This can
    work sanely when only a single set of input devices is used at any given
    time. The keyboard and pointer state will be handled in the front-end, with
    changes propagated to the back-end servers as needed. This option was
    implemented and works well. Because the core pointer on a back-end controls
    the hardware mouse on that back-end, core pointers cannot be treated as
    XInput extension devices. However, all back-end XInput extensions devices
    can be mapped to either DMX core or DMX XInput extension devices.

 3. Console Input. The front-end server could create a console window that is
    displayed on an X server independent of the back-end X servers. This
    console window could display things like the physical screen layout, and
    the front-end could get its core input events from events delivered to the
    console window. This option was implemented and works well. To help the
    human navigate, window outlines are also displayed in the console window.
    Further, console windows can be used as either core or XInput extension
    devices.

 4. Other options were initially explored, but they were all partial subsets of
    the options listed above and, hence, are irrelevant.

Although extended input devices are not specifically mentioned in the
Distributed X requirements, the options above were all implemented so that
XInput extension devices were supported.

The bootstrap code (Xdmx) had dummy input devices, and these are still
supported in the final version. These do the necessary initialization to
satisfy the X server's requirements for core pointer and keyboard devices, but
no input events are ever generated.

Status: The input code is complete. Because of the complexity of the XFree86
input device drivers (and their heavy reliance on XFree86 infrastructure),
separate low-level device drivers were implemented for Xdmx. The following
kinds of drivers are supported (in general, the devices can be treated
arbitrarily as "core" input devices or as XInput "extension" devices; and
multiple instances of different kinds of devices can be simultaneously
available):

 1. A "dummy" device drive that never generates events.

 2. "Local" input is from the low-level hardware on which the Xdmx binary is
    running. This is the only area where using the XFree86 driver
    infrastructure would have been helpful, and then only partially, since good
    support for generic USB devices does not yet exist in XFree86 (in any case,
    XFree86 and kdrive driver code was used where possible). Currently, the
    following local devices are supported under Linux (porting to other
    operating systems should be fairly straightforward):

      ● Linux keyboard

      ● Linux serial mouse (MS)

      ● Linux PS/2 mouse

      ● USB keyboard

      ● USB mouse

      ● USB generic device (e.g., joystick, gamepad, etc.)

 3. "Backend" input is taken from one or more of the back-end displays. In this
    case, events are taken from the back-end X server and are converted to Xdmx
    events. Care must be taken so that the sprite moves properly on the display
    from which input is being taken.

 4. "Console" input is taken from an X window that Xdmx creates on the
    operator's display (i.e., on the machine running the Xdmx binary). When the
    operator's mouse is inside the console window, then those events are
    converted to Xdmx events. Several special features are available: the
    console can display outlines of windows that are on the Xdmx display (to
    facilitate navigation), the cursor can be confined to the console, and a
    "fine" mode can be activated to allow very precise cursor positioning.

Output device handling

The output of the DMX system displays rendering and windowing requests across
multiple screens. The screens are typically arranged in a grid such that
together they represent a single large display.

The output section of the DMX code consists of two parts. The first is in the
front-end proxy X server (Xdmx), which accepts client connections, manages the
windows, and potentially renders primitives but does not actually display any
of the drawing primitives. The second part is the back-end X server(s), which
accept commands from the front-end server and display the results on their
screens.

Initialization

The DMX front-end must first initialize its screens by connecting to each of
the back-end X servers and collecting information about each of these screens.
However, the information collected from the back-end X servers might be
inconsistent. Handling these cases can be difficult and/or inefficient. For
example, a two screen system has one back-end X server running at 16bpp while
the second is running at 32bpp. Converting rendering requests (e.g., XPutImage
() or XGetImage() requests) to the appropriate bit depth can be very time
consuming. Analyzing these cases to determine how or even if it is possible to
handle them is required. The current Xinerama code handles many of these cases
(e.g., in PanoramiXConsolidate()) and will be used as a starting point. In
general, the best solution is to use homogeneous X servers and display devices.
Using back-end servers with the same depth is a requirement of the final DMX
implementation.

Once this screen consolidation is finished, the relative position of each
back-end X server's screen in the unified screen is initialized. A full-screen
window is opened on each of the back-end X servers, and the cursor on each
screen is turned off. The final DMX implementation can also make use of a
partial-screen window, or multiple windows per back-end screen.

Handling rendering requests

After initialization, X applications connect to the front-end server. There are
two possible implementations of how rendering and windowing requests are
handled in the DMX system:

 1. A shadow framebuffer is used in the front-end server as the render target.
    In this option, all protocol requests are completely handled in the
    front-end server. All state and resources are maintained in the front-end
    including a shadow copy of the entire framebuffer. The framebuffers
    attached to the back-end servers are updated by XPutImage() calls with data
    taken directly from the shadow framebuffer.

    This solution suffers from two main problems. First, it does not take
    advantage of any accelerated hardware available in the system. Second, the
    size of the XPutImage() calls can be quite large and thus will be limited
    by the bandwidth available.

    The initial DMX implementation used a shadow framebuffer by default.

 2. Rendering requests are sent to each back-end server for handling (as is
    done in the Xnest server described above). In this option, certain protocol
    requests are handled in the front-end server and certain requests are
    repackaged and then sent to the back-end servers. The framebuffer is
    distributed across the multiple back-end servers. Rendering to the
    framebuffer is handled on each back-end and can take advantage of any
    acceleration available on the back-end servers' graphics display device.
    State is maintained both in the front and back-end servers.

    This solution suffers from two main drawbacks. First, protocol requests are
    sent to all back-end servers -- even those that will completely clip the
    rendering primitive -- which wastes bandwidth and processing time. Second,
    state is maintained both in the front- and back-end servers. These
    drawbacks are not as severe as in option 1 (above) and can either be
    overcome through optimizations or are acceptable. Therefore, this option
    will be used in the final implementation.

    The final DMX implementation defaults to this mechanism, but also supports
    the shadow framebuffer mechanism. Several optimizations were implemented to
    eliminate the drawbacks of the default mechanism. These optimizations are
    described the section below and in Phase II of the Development Results (see
    appendix).

Status: Both the shadow framebuffer and Xnest-style code is complete.

Optimizing DMX

Initially, the Xnest-style solution's performance will be measured and analyzed
to determine where the performance bottlenecks exist. There are four main areas
that will be addressed.

First, to obtain reasonable interactivity with the first development phase,
XSync() was called after each protocol request. The XSync() function flushes
any pending protocol requests. It then waits for the back-end to process the
request and send a reply that the request has completed. This happens with each
back-end server and performance greatly suffers. As a result of the way XSync()
is called in the first development phase, the batching that the X11 library
performs is effectively defeated. The XSync() call usage will be analyzed and
optimized by batching calls and performing them at regular intervals, except
where interactivity will suffer (e.g., on cursor movements).

Second, the initial Xnest-style solution described above sends the repackaged
protocol requests to all back-end servers regardless of whether or not they
would be completely clipped out. The requests that are trivially rejected on
the back-end server wastes the limited bandwidth available. By tracking
clipping changes in the DMX X server's windowing code (e.g., by opening,
closing, moving or resizing windows), we can determine whether or not back-end
windows are visible so that trivial tests in the front-end server's GC ops
drawing functions can eliminate these unnecessary protocol requests.

Third, each protocol request will be analyzed to determine if it is possible to
break the request into smaller pieces at display boundaries. The initial ones
to be analyzed are put and get image requests since they will require the
greatest bandwidth to transmit data between the front and back-end servers.
Other protocol requests will be analyzed and those that will benefit from
breaking them into smaller requests will be implemented.

Fourth, an extension is being considered that will allow font glyphs to be
transferred from the front-end DMX X server to each back-end server. This
extension will permit the front-end to handle all font requests and eliminate
the requirement that all back-end X servers share the exact same fonts as the
front-end server. We are investigating the feasibility of this extension during
this development phase.

Other potential optimizations will be determined from the performance analysis.

Please note that in our initial design, we proposed optimizing BLT operations
(e.g., XCopyArea() and window moves) by developing an extension that would
allow individual back-end servers to directly copy pixel data to other back-end
servers. This potential optimization was in response to the simple image
movement implementation that required potentially many calls to GetImage() and
PutImage(). However, the current Xinerama implementation handles these BLT
operations differently. Instead of copying data to and from screens, they
generate expose events -- just as happens in the case when a window is moved
from off a screen to on screen. This approach saves the limited bandwidth
available between front and back-end servers and is being standardized with
Xinerama. It also eliminates the potential setup problems and security issues
resulting from having each back-end server open connections to all other
back-end servers. Therefore, we suggest accepting Xinerama's expose event
solution.

Also note that the approach proposed in the second and third optimizations
might cause backing store algorithms in the back-end to be defeated, so a DMX X
server configuration flag will be added to disable these optimizations.

Status: The optimizations proposed above are complete. It was determined that
the using the xfs font server was sufficient and creating a new mechanism to
pass glyphs was redundant; therefore, the fourth optimization proposed above
was not included in DMX.

DMX X extension support

The DMX X server keeps track of all the windowing information on the back-end X
servers, but does not currently export this information to any client
applications. An extension will be developed to pass the screen information and
back-end window IDs to DMX-aware clients. These clients can then use this
information to directly connect to and render to the back-end windows.
Bypassing the DMX X server allows DMX-aware clients to break up complex
rendering requests on their own and send them directly to the windows on the
back-end server's screens. An example of a client that can make effective use
of this extension is Chromium.

Status: The extension, as implemented, is fully documented in "Client-to-Server
DMX Extension to the X Protocol". Future changes might be required based on
feedback and other proposed enhancements to DMX. Currently, the following
facilities are supported:

 1. Screen information (clipping rectangle for each screen relative to the
    virtual screen)

 2. Window information (window IDs and clipping information for each back-end
    window that corresponds to each DMX window)

 3. Input device information (mappings from DMX device IDs to back-end device
    IDs)

 4. Force window creation (so that a client can override the server-side lazy
    window creation optimization)

 5. Reconfiguration (so that a client can request that a screen position be
    changed)

 6. Addition and removal of back-end servers and back-end and console inputs.

Common X extension support

The XInput, XKeyboard and Shape extensions are commonly used extensions to the
base X11 protocol. XInput allows multiple and non-standard input devices to be
accessed simultaneously. These input devices can be connected to either the
front-end or back-end servers. XKeyboard allows much better keyboard mappings
control. Shape adds support for arbitrarily shaped windows and is used by
various window managers. Nearly all potential back-end X servers make these
extensions available, and support for each one will be added to the DMX system.

In addition to the extensions listed above, support for the X Rendering
extension (Render) is being developed. Render adds digital image composition to
the rendering model used by the X Window System. While this extension is still
under development by Keith Packard of HP, support for the current version will
be added to the DMX system.

Support for the XTest extension was added during the first development phase.

Status: The following extensions are supported and are discussed in more detail
in Phase IV of the Development Results (see appendix): BIG-REQUESTS, DEC-XTRAP,
DMX, DPMS, Extended-Visual-Information, GLX, LBX, RECORD, RENDER, SECURITY,
SHAPE, SYNC, X-Resource, XC-APPGROUP, XC-MISC, XFree86-Bigfont, XINERAMA,
XInputExtension, XKEYBOARD, and XTEST.

OpenGL support

OpenGL support using the Mesa code base exists in XFree86 release 4 and later.
Currently, the direct rendering infrastructure (DRI) provides accelerated
OpenGL support for local clients and unaccelerated OpenGL support (i.e.,
software rendering) is provided for non-local clients.

The single head OpenGL support in XFree86 4.x will be extended to use the DMX
system. When the front and back-end servers are on the same physical hardware,
it is possible to use the DRI to directly render to the back-end servers.
First, the existing DRI will be extended to support multiple display heads, and
then to support the DMX system. OpenGL rendering requests will be direct
rendering to each back-end X server. The DRI will request the screen layout
(either from the existing Xinerama extension or a DMX-specific extension).
Support for synchronized swap buffers will also be added (on hardware that
supports it). Note that a single front-end server with a single back-end server
on the same physical machine can emulate accelerated indirect rendering.

When the front and back-end servers are on different physical hardware or are
using non-XFree86 4.x X servers, a mechanism to render primitives across the
back-end servers will be provided. There are several options as to how this can
be implemented.

 1. The existing OpenGL support in each back-end server can be used by
    repackaging rendering primitives and sending them to each back-end server.
    This option is similar to the unoptimized Xnest-style approach mentioned
    above. Optimization of this solution is beyond the scope of this project
    and is better suited to other distributed rendering systems.

 2. Rendering to a pixmap in the front-end server using the current XFree86 4.x
    code, and then displaying to the back-ends via calls to XPutImage() is
    another option. This option is similar to the shadow frame buffer approach
    mentioned above. It is slower and bandwidth intensive, but has the
    advantage that the back-end servers are not required to have OpenGL
    support.

These, and other, options will be investigated in this phase of the work.

Work by others have made Chromium DMX-aware. Chromium will use the DMX X
protocol extension to obtain information about the back-end servers and will
render directly to those servers, bypassing DMX.

Status: OpenGL support by the glxProxy extension was implemented by SGI and has
been integrated into the DMX code base.

Current issues

In this sections the current issues are outlined that require further
investigation.

Fonts

The font path and glyphs need to be the same for the front-end and each of the
back-end servers. Font glyphs could be sent to the back-end servers as
necessary but this would consume a significant amount of available bandwidth
during font rendering for clients that use many different fonts (e.g.,
Netscape). Initially, the font server (xfs) will be used to provide the fonts
to both the front-end and back-end servers. Other possibilities will be
investigated during development.

Zero width rendering primitives

To allow pixmap and on-screen rendering to be pixel perfect, all back-end
servers must render zero width primitives exactly the same as the front-end
renders the primitives to pixmaps. For those back-end servers that do not
exactly match, zero width primitives will be automatically converted to one
width primitives. This can be handled in the front-end server via the GC state.

Output scaling

With very large tiled displays, it might be difficult to read the information
on the standard X desktop. In particular, the cursor can be easily lost and
fonts could be difficult to read. Automatic primitive scaling might prove to be
very useful. We will investigate the possibility of scaling the cursor and
providing a set of alternate pre-scaled fonts to replace the standard fonts
that many applications use (e.g., fixed). Other options for automatic scaling
will also be investigated.

Per-screen colormaps

Each screen's default colormap in the set of back-end X servers should be able
to be adjusted via a configuration utility. This support is would allow the
back-end screens to be calibrated via custom gamma tables. On 24-bit systems
that support a DirectColor visual, this type of correction can be accommodated.
One possible implementation would be to advertise to X client of the DMX server
a TrueColor visual while using DirectColor visuals on the back-end servers to
implement this type of color correction. Other options will be investigated.

A. Appendix

Background

This section describes the existing Open Source architectures that can be used
to handle multiple screens and upon which this development project is based.
This section was written before the implementation was finished, and may not
reflect actual details of the implementation. It is left for historical
interest only.

Core input device handling

The following is a description of how core input devices are handled by an X
server.

InitInput()

InitInput() is a DDX function that is called at the start of each server
generation from the X server's main() function. Its purpose is to determine
what input devices are connected to the X server, register them with the DIX
and MI layers, and initialize the input event queue. InitInput() does not have
a return value, but the X server will abort if either a core keyboard device or
a core pointer device are not registered. Extended input (XInput) devices can
also be registered in InitInput().

InitInput() usually has implementation specific code to determine which input
devices are available. For each input device it will be using, it calls
AddInputDevice():

               This DIX function allocates the device structure, registers a
AddInputDevice callback function (which handles device init, close, on and
()             off), and returns the input handle, which can be treated as
               opaque. It is called once for each input device.

Once input handles for core keyboard and core pointer devices have been
obtained from AddInputDevice(), they are registered as core devices by calling
RegisterPointerDevice() and RegisterKeyboardDevice(). Each of these should be
called once. If both core devices are not registered, then the X server will
exit with a fatal error when it attempts to start the input devices in
InitAndStartDevices(), which is called directly after InitInput() (see below).

Register           These DIX functions take a handle returned from
{Pointer,Keyboard} AddInputDevice() and initialize the core input device fields
Device()           in inputInfo, and initialize the input processing and grab
                   functions for each core input device.

The core pointer device is then registered with the miPointer code (which does
the high level cursor handling). While this registration is not necessary for
correct miPointer operation in the current XFree86 code, it is still done
mostly for compatibility reasons.

miRegisterPointerDevice This MI function registers the core pointer's input
()                      handle with with the miPointer code.

The final part of InitInput() is the initialization of the input event queue
handling. In most cases, the event queue handling provided in the MI layer is
used. The primary XFree86 X server uses its own event queue handling to support
some special cases related to the XInput extension and the XFree86-specific DGA
extension. For our purposes, the MI event queue handling should be suitable. It
is initialized by calling mieqInit():

mieqInit This MI function initializes the MI event queue for the core devices,
()       and is passed the public component of the input handles for the two
         core devices.

If a wakeup handler is required to deliver synchronous input events, it can be
registered here by calling the DIX function RegisterBlockAndWakeupHandlers().
(See the devReadInput() description below.)

InitAndStartDevices()

InitAndStartDevices() is a DIX function that is called immediately after
InitInput() from the X server's main() function. Its purpose is to initialize
each input device that was registered with AddInputDevice(), enable each input
device that was successfully initialized, and create the list of enabled input
devices. Once each registered device is processed in this way, the list of
enabled input devices is checked to make sure that both a core keyboard device
and core pointer device were registered and successfully enabled. If not,
InitAndStartDevices() returns failure, and results in the the X server exiting
with a fatal error.

Each registered device is initialized by calling its callback (dev->deviceProc)
with the DEVICE_INIT argument:

              This function initializes the device structs with core
              information relevant to the device.

              For pointer devices, this means specifying the number of buttons,
              default button mapping, the function used to get motion events
(*dev->       (usually miPointerGetMotionEvents()), the function used to change
deviceProc)   /control the core pointer motion parameters (acceleration and
(dev,         threshold), and the motion buffer size.
DEVICE_INIT)
              For keyboard devices, this means specifying the keycode range,
              default keycode to keysym mapping, default modifier mapping, and
              the functions used to sound the keyboard bell and modify/control
              the keyboard parameters (LEDs, bell pitch and duration, key
              click, which keys are auto-repeating, etc).

Each initialized device is enabled by calling EnableDevice():

             EnableDevice() calls the device callback with DEVICE_ON:

             (*dev->       This typically opens and initializes the relevant
EnableDevice deviceProc)   physical device, and when appropriate, registers the
()           (dev,         device's file descriptor (or equivalent) as a valid
             DEVICE_ON)    input source.

             EnableDevice() then adds the device handle to the X server's
             global list of enabled devices.

InitAndStartDevices() then verifies that a valid core keyboard and pointer has
been initialized and enabled. It returns failure if either are missing.

devReadInput()

Each device will have some function that gets called to read its physical
input. These may be called in a number of different ways. In the case of
synchronous I/O, they will be called from a DDX wakeup-handler that gets called
after the server detects that new input is available. In the case of
asynchronous I/O, they will be called from a (SIGIO) signal handler triggered
when new input is available. This function should do at least two things: make
sure that input events get enqueued, and make sure that the cursor gets moved
for motion events (except if these are handled later by the driver's own event
queue processing function, which cannot be done when using the MI event queue
handling).

Events are queued by calling mieqEnqueue():

mieqEnqueue This MI function is used to add input events to the event queue. It
()          is simply passed the event to be queued.

The cursor position should be updated when motion events are enqueued, by
calling either miPointerAbsoluteCursor() or miPointerDeltaCursor():

miPointerAbsoluteCursor This MI function is used to move the cursor to the
()                      absolute coordinates provided.

miPointerDeltaCursor()  This MI function is used to move the cursor relative to
                        its current position.

ProcessInputEvents()

ProcessInputEvents() is a DDX function that is called from the X server's main
dispatch loop when new events are available in the input event queue. It
typically processes the enqueued events, and updates the cursor/pointer
position. It may also do other DDX-specific event processing.

Enqueued events are processed by mieqProcessInputEvents() and passed to the DIX
layer for transmission to clients:

                       This function processes each event in the event queue,
mieqProcessInputEvents and passes it to the device's input processing function.
()                     The DIX layer provides default functions to do this
                       processing, and they handle the task of getting the
                       events passed back to the relevant clients.

                       This function resynchronized the cursor position with
miPointerUpdate()      the new pointer position. It also takes care of moving
                       the cursor between screens when needed in multi-head
                       configurations.

DisableDevice()

DisableDevice is a DIX function that removes an input device from the list of
enabled devices. The result of this is that the device no longer generates
input events. The device's data structures are kept in place, and disabling a
device like this can be reversed by calling EnableDevice(). DisableDevice() may
be called from the DDX when it is desirable to do so (e.g., the XFree86 server
does this when VT switching). Except for special cases, this is not normally
called for core input devices.

DisableDevice() calls the device's callback function with DEVICE_OFF:

(*dev->          This typically closes the relevant physical device, and when
deviceProc)(dev, appropriate, unregisters the device's file descriptor (or
DEVICE_OFF)      equivalent) as a valid input source.

DisableDevice() then removes the device handle from the X server's global list
of enabled devices.

CloseDevice()

CloseDevice is a DIX function that removes an input device from the list of
available devices. It disables input from the device and frees all data
structures associated with the device. This function is usually called from
CloseDownDevices(), which is called from main() at the end of each server
generation to close all input devices.

CloseDevice() calls the device's callback function with DEVICE_CLOSE:

(*dev->        This typically closes the relevant physical device, and when
deviceProc)    appropriate, unregisters the device's file descriptor (or
(dev,          equivalent) as a valid input source. If any device specific data
DEVICE_CLOSE)  structures were allocated when the device was initialized, they
               are freed here.

CloseDevice() then frees the data structures that were allocated for the device
when it was registered/initialized.

LegalModifier()

LegalModifier() is a required DDX function that can be used to restrict which
keys may be modifier keys. This seems to be present for historical reasons, so
this function should simply return TRUE unconditionally.

Output handling

The following sections describe the main functions required to initialize, use
and close the output device(s) for each screen in the X server.

InitOutput()

This DDX function is called near the start of each server generation from the X
server's main() function. InitOutput()'s main purpose is to initialize each
screen and fill in the global screenInfo structure for each screen. It is
passed three arguments: a pointer to the screenInfo struct, which it is to
initialize, and argc and argv from main(), which can be used to determine
additional configuration information.

The primary tasks for this function are outlined below:

 1. Parse configuration info: The first task of InitOutput() is to parses any
    configuration information from the configuration file. In addition to the
    XF86Config file, other configuration information can be taken from the
    command line. The command line options can be gathered either in InitOutput
    () or earlier in the ddxProcessArgument() function, which is called by
    ProcessCommandLine(). The configuration information determines the
    characteristics of the screen(s). For example, in the XFree86 X server, the
    XF86Config file specifies the monitor information, the screen resolution,
    the graphics devices and slots in which they are located, and, for
    Xinerama, the screens' layout.

 2. Initialize screen info: The next task is to initialize the screen-dependent
    internal data structures. For example, part of what the XFree86 X server
    does is to allocate its screen and pixmap private indices, probe for
    graphics devices, compare the probed devices to the ones listed in the
    XF86Config file, and add the ones that match to the internal xf86Screens[]
    structure.

 3. Set pixmap formats: The next task is to initialize the screenInfo's image
    byte order, bitmap bit order and bitmap scanline unit/pad. The screenInfo's
    pixmap format's depth, bits per pixel and scanline padding is also
    initialized at this stage.

 4. Unify screen info: An optional task that might be done at this stage is to
    compare all of the information from the various screens and determines if
    they are compatible (i.e., if the set of screens can be unified into a
    single desktop). This task has potential to be useful to the DMX front-end
    server, if Xinerama's PanoramiXConsolidate() function is not sufficient.

Once these tasks are complete, the valid screens are known and each of these
screens can be initialized by calling AddScreen().

AddScreen()

This DIX function is called from InitOutput(), in the DDX layer, to add each
new screen to the screenInfo structure. The DDX screen initialization function
and command line arguments (i.e., argc and argv) are passed to it as arguments.

This function first allocates a new Screen structure and any privates that are
required. It then initializes some of the fields in the Screen struct and sets
up the pixmap padding information. Finally, it calls the DDX screen
initialization function ScreenInit(), which is described below. It returns the
number of the screen that were just added, or -1 if there is insufficient
memory to add the screen or if the DDX screen initialization fails.

ScreenInit()

This DDX function initializes the rest of the Screen structure with either
generic or screen-specific functions (as necessary). It also fills in various
screen attributes (e.g., width and height in millimeters, black and white pixel
values).

The screen init function usually calls several functions to perform certain
screen initialization functions. They are described below:

                         The DDX layer's ScreenInit() function usually calls
                         another layer's ScreenInit() function (e.g.,
                         miScreenInit() or fbScreenInit()) to initialize the
                         fallbacks that the DDX driver does not specifically
                         handle.

{mi,*fb}ScreenInit()     After calling another layer's ScreenInit() function,
                         any screen-specific functions either wrap or replace
                         the other layer's function pointers. If a function is
                         to be wrapped, each of the old function pointers from
                         the other layer are stored in a screen private area.
                         Common functions to wrap are CloseScreen() and
                         SaveScreen().

miInitializeBackingStore This MI function initializes the screen's backing
()                       storage functions, which are used to save areas of
                         windows that are currently covered by other windows.

                         This MI function initializes the MI cursor display
                         structures and function pointers. If a hardware cursor
miDCInitialize()         is used, the DDX layer's ScreenInit() function will
                         wrap additional screen and the MI cursor display
                         function pointers.

Another common task for ScreenInit() function is to initialize the output
device state. For example, in the XFree86 X server, the ScreenInit() function
saves the original state of the video card and then initializes the video mode
of the graphics device.

CloseScreen()

This function restores any wrapped screen functions (and in particular the
wrapped CloseScreen() function) and restores the state of the output device to
its original state. It should also free any private data it created during the
screen initialization.

GC operations

When the X server is requested to render drawing primitives, it does so by
calling drawing functions through the graphics context's operation function
pointer table (i.e., the GCOps functions). These functions render the basic
graphics operations such as drawing rectangles, lines, text or copying pixmaps.
Default routines are provided either by the MI layer, which draws indirectly
through a simple span interface, or by the framebuffer layers (e.g., CFB, MFB,
FB), which draw directly to a linearly mapped frame buffer.

To take advantage of special hardware on the graphics device, specific GCOps
functions can be replaced by device specific code. However, many times the
graphics devices can handle only a subset of the possible states of the GC, so
during graphics context validation, appropriate routines are selected based on
the state and capabilities of the hardware. For example, some graphics hardware
can accelerate single pixel width lines with certain dash patterns. Thus, for
dash patterns that are not supported by hardware or for width 2 or greater
lines, the default routine is chosen during GC validation.

Note that some pointers to functions that draw to the screen are stored in the
Screen structure. They include GetImage(), GetSpans(), CopyWindow() and
RestoreAreas().

Xnest

The Xnest X server is a special proxy X server that relays the X protocol
requests that it receives to a ``real'' X server that then processes the
requests and displays the results, if applicable. To the X applications, Xnest
appears as if it is a regular X server. However, Xnest is both server to the X
application and client of the real X server, which will actually handle the
requests.

The Xnest server implements all of the standard input and output initialization
steps outlined above.

            Xnest takes its configuration information from command line
            arguments via ddxProcessArguments(). This information includes the
            real X server display to connect to, its default visual class, the
            screen depth, the Xnest window's geometry, etc. Xnest then connects
            to the real X server and gathers visual, colormap, depth and pixmap
InitOutput  information about that server's display, creates a window on that
()          server, which will be used as the root window for Xnest.

            Next, Xnest initializes its internal data structures and uses the
            data from the real X server's pixmaps to initialize its own pixmap
            formats. Finally, it calls AddScreen(xnestOpenScreen, argc, argv)
            to initialize each of its screens.

            Xnest's ScreenInit() function is called xnestOpenScreen(). This
            function initializes its screen's depth and visual information, and
            then calls miScreenInit() to set up the default screen functions.
ScreenInit  It then calls miInitializeBackingStore() and miDCInitialize() to
()          initialize backing store and the software cursor. Finally, it
            replaces many of the screen functions with its own functions that
            repackage and send the requests to the real X server to which Xnest
            is attached.

            This function frees its internal data structure allocations. Since
CloseScreen it replaces instead of wrapping screen functions, there are no
()          function pointers to unwrap. This can potentially lead to problems
            during server regeneration.

            The GC operations in Xnest are very simple since they leave all of
            the drawing to the real X server to which Xnest is attached. Each
            of the GCOps takes the request and sends it to the real X server
            using standard Xlib calls. For example, the X application issues a
            XDrawLines() call. This function turns into a protocol request to
            Xnest, which calls the xnestPolylines() function through Xnest's
            GCOps function pointer table. The xnestPolylines() function is only
            a single line, which calls XDrawLines() using the same arguments
            that were passed into it. Other GCOps functions are very similar.
            Two exceptions to the simple GCOps functions described above are
            the image functions and the BLT operations.

GC          The image functions, GetImage() and PutImage(), must use a
operations  temporary image to hold the image to be put of the image that was
            just grabbed from the screen while it is in transit to the real X
            server or the client. When the image has been transmitted, the
            temporary image is destroyed.

            The BLT operations, CopyArea() and CopyPlane(), handle not only the
            copy function, which is the same as the simple cases described
            above, but also the graphics exposures that result when the GC's
            graphics exposure bit is set to True. Graphics exposures are
            handled in a helper function, xnestBitBlitHelper(). This function
            collects the exposure events from the real X server and, if any
            resulting in regions being exposed, then those regions are passed
            back to the MI layer so that it can generate exposure events for
            the X application.

The Xnest server takes its input from the X server to which it is connected.
When the mouse is in the Xnest server's window, keyboard and mouse events are
received by the Xnest server, repackaged and sent back to any client that
requests those events.

Shadow framebuffer

The most common type of framebuffer is a linear array memory that maps to the
video memory on the graphics device. However, accessing that video memory over
an I/O bus (e.g., ISA or PCI) can be slow. The shadow framebuffer layer allows
the developer to keep the entire framebuffer in main memory and copy it back to
video memory at regular intervals. It also has been extended to handle planar
video memory and rotated framebuffers.

There are two main entry points to the shadow framebuffer code:

shadowAlloc   This function allocates the in memory copy of the framebuffer of
(width,       size width*height*bpp. It returns a pointer to that memory, which
height, bpp)  will be used by the framebuffer ScreenInit() code during the
              screen's initialization.

              This function initializes the shadow framebuffer layer. It wraps
              several screen drawing functions, and registers a block handler
shadowInit    that will update the screen. The updateProc is a function that
(pScreen,     will copy the damaged regions to the screen, and the windowProc
updateProc,   is a function that is used when the entire linear video memory
windowProc)   range cannot be accessed simultaneously so that only a window
              into that memory is available (e.g., when using the VGA
              aperture).

The shadow framebuffer code keeps track of the damaged area of each screen by
calculating the bounding box of all drawing operations that have occurred since
the last screen update. Then, when the block handler is next called, only the
damaged portion of the screen is updated.

Note that since the shadow framebuffer is kept in main memory, all drawing
operations are performed by the CPU and, thus, no accelerated hardware drawing
operations are possible.

Xinerama

Xinerama is an X extension that allows multiple physical screens controlled by
a single X server to appear as a single screen. Although the extension allows
clients to find the physical screen layout via extension requests, it is
completely transparent to clients at the core X11 protocol level. The original
public implementation of Xinerama came from Digital/Compaq. XFree86 rewrote it,
filling in some missing pieces and improving both X11 core protocol compliance
and performance. The Xinerama extension will be passing through X.Org's
standardization process in the near future, and the sample implementation will
be based on this rewritten version.

The current implementation of Xinerama is based primarily in the DIX (device
independent) and MI (machine independent) layers of the X server. With few
exceptions the DDX layers do not need any changes to support Xinerama. X server
extensions often do need modifications to provide full Xinerama functionality.

The following is a code-level description of how Xinerama functions.

Note: Because the Xinerama extension was originally called the PanoramiX
extension, many of the Xinerama functions still have the PanoramiX prefix.

                               PanoramiXExtensionInit() is a device-independent
                               extension function that is called at the start
                               of each server generation from InitExtensions(),
                               which is called from the X server's main()
                               function after all output devices have been
                               initialized, but before any input devices have
                               been initialized.

                               PanoramiXNumScreens is set to the number of
                               physical screens. If only one physical screen is
                               present, the extension is disabled, and
                               PanoramiXExtensionInit() returns without doing
                               anything else.

                               The Xinerama extension is registered by calling
                               AddExtension().

                               GC and Screen private indexes are allocated, and
                               both GC and Screen private areas are allocated
                               for each physical screen. These hold
                               Xinerama-specific per-GC and per-Screen data.
                               Each screen's CreateGC and CloseScreen functions
                               are wrapped by XineramaCreateGC() and
                               XineramaCloseScreen() respectively. Some new
                               resource classes are created for Xinerama
                               drawables and GCs, and resource types for
PanoramiXExtensionInit()       Xinerama windows, pixmaps and colormaps.

                               A region (PanoramiXScreenRegion) is initialized
                               to be the union of the screen regions. The
                               relative positioning information for the
                               physical screens is taken from the ScreenRec x
                               and y members, which the DDX layer must
                               initialize in InitOutput(). The bounds of the
                               combined screen is also calculated
                               (PanoramiXPixWidth and PanoramiXPixHeight).

                               The DIX layer has a list of function pointers
                               (ProcVector[]) that holds the entry points for
                               the functions that process core protocol
                               requests. The requests that Xinerama must
                               intercept and break up into physical
                               screen-specific requests are wrapped. The
                               original set is copied to SavedProcVector[]. The
                               types of requests intercepted are Window
                               requests, GC requests, colormap requests,
                               drawing requests, and some geometry-related
                               requests. This wrapping allows the bulk of the
                               protocol request processing to be handled
                               transparently to the DIX layer. Some operations
                               cannot be dealt with in this way and are handled
                               with Xinerama-specific code within the DIX
                               layer.

                               PanoramiXConsolidate() is a device-independent
                               extension function that is called directly from
                               the X server's main() function after extensions
                               and input/output devices have been initialized,
                               and before the root windows are defined and
                               initialized.

                               This function finds the set of depths
PanoramiXConsolidate()         (PanoramiXDepths[]) and visuals
                               (PanoramiXVisuals[]) common to all of the
                               physical screens. PanoramiXNumDepths is set to
                               the number of common depths, and
                               PanoramiXNumVisuals is set to the number of
                               common visuals. Resources are created for the
                               single root window and the default colormap.
                               Each of these resources has per-physical screen
                               entries.

                               PanoramiXConsolidate() is a device-independent
                               extension function that is called directly from
                               the X server's main() function after the
                               per-physical screen root windows are created. It
                               is called instead of the standard DIX
                               CreateConnectionBlock() function. If this
                               function returns FALSE, the X server exits with
                               a fatal error. This function will return FALSE
                               if no common depths were found in
                               PanoramiXConsolidate(). With no common depths,
                               Xinerama mode is not possible.

                               The connection block holds the information that
                               clients get when they open a connection to the X
                               server. It includes information such as the
PanoramiXCreateConnectionBlock supported pixmap formats, number of screens and
()                             the sizes, depths, visuals, default colormap
                               information, etc, for each of the screens (much
                               of information that xdpyinfo shows). The
                               connection block is initialized with the
                               combined single screen values that were
                               calculated in the above two functions.

                               The Xinerama extension allows the registration
                               of connection block callback functions. The
                               purpose of these is to allow other extensions to
                               do processing at this point. These callbacks can
                               be registered by calling
                               XineramaRegisterConnectionBlockCallback() from
                               the other extension's ExtensionInit() function.
                               Each registered connection block callback is
                               called at the end of
                               PanoramiXCreateConnectionBlock().

Xinerama-specific changes to the DIX code

There are a few types of Xinerama-specific changes within the DIX code. The
main ones are described here.

Functions that deal with colormap or GC -related operations outside of the
intercepted protocol requests have a test added to only do the processing for
screen numbers > 0. This is because they are handled for the single Xinerama
screen and the processing is done once for screen 0.

The handling of motion events does some coordinate translation between the
physical screen's origin and screen zero's origin. Also, motion events must be
reported relative to the composite screen origin rather than the physical
screen origins.

There is some special handling for cursor, window and event processing that
cannot (either not at all or not conveniently) be done via the intercepted
protocol requests. A particular case is the handling of pointers moving between
physical screens.

Xinerama-specific changes to the MI code

The only Xinerama-specific change to the MI code is in miSendExposures() to
handle the coordinate (and window ID) translation for expose events.

Intercepted DIX core requests

Xinerama breaks up drawing requests for dispatch to each physical screen. It
also breaks up windows into pieces for each physical screen. GCs are translated
into per-screen GCs. Colormaps are replicated on each physical screen. The
functions handling the intercepted requests take care of breaking the requests
and repackaging them so that they can be passed to the standard request
handling functions for each screen in turn. In addition, and to aid the
repackaging, the information from many of the intercepted requests is used to
keep up to date the necessary state information for the single composite
screen. Requests (usually those with replies) that can be satisfied completely
from this stored state information do not call the standard request handling
functions.

Development Results

In this section the results of each phase of development are discussed. This
development took place between approximately June 2001 and July 2003.

Phase I

The initial development phase dealt with the basic implementation including the
bootstrap code, which used the shadow framebuffer, and the unoptimized
implementation, based on an Xnest-style implementation.

Scope

The goal of Phase I is to provide fundamental functionality that can act as a
foundation for ongoing work:

 1. Develop the proxy X server

      ● The proxy X server will operate on the X11 protocol and relay requests
        as necessary to correctly perform the request.

      ● Work will be based on the existing work for Xinerama and Xnest.

      ● Input events and windowing operations are handled in the proxy server
        and rendering requests are repackaged and sent to each of the back-end
        servers for display.

      ● The multiple screen layout (including support for overlapping screens)
        will be user configurable via a configuration file or through the
        configuration tool.

 2. Develop graphical configuration tool

      ● There will be potentially a large number of X servers to configure into
        a single display. The tool will allow the user to specify which servers
        are involved in the configuration and how they should be laid out.

 3. Pass the X Test Suite

      ● The X Test Suite covers the basic X11 operations. All tests known to
        succeed must correctly operate in the distributed X environment.

For this phase, the back-end X servers are assumed to be unmodified X servers
that do not support any DMX-related protocol extensions; future optimization
pathways are considered, but are not implemented; and the configuration tool is
assumed to rely only on libraries in the X source tree (e.g., Xt).

Results

The proxy X server, Xdmx, was developed to distribute X11 protocol requests to
the set of back-end X servers. It opens a window on each back-end server, which
represents the part of the front-end's root window that is visible on that
screen. It mirrors window, pixmap and other state in each back-end server.
Drawing requests are sent to either windows or pixmaps on each back-end server.
This code is based on Xnest and uses the existing Xinerama extension.

Input events can be taken from (1) devices attached to the back-end server, (2)
core devices attached directly to the Xdmx server, or (3) from a ``console''
window on another X server. Events for these devices are gathered, processed
and delivered to clients attached to the Xdmx server.

An intuitive configuration format was developed to help the user easily
configure the multiple back-end X servers. It was defined (see grammar in Xdmx
man page) and a parser was implemented that is used by the Xdmx server and by a
standalone xdmxconfig utility. The parsing support was implemented such that it
can be easily factored out of the X source tree for use with other tools (e.g.,
vdl). Support for converting legacy vdl-format configuration files to the DMX
format is provided by the vdltodmx utility.

Originally, the configuration file was going to be a subsection of XFree86's
XF86Config file, but that was not possible since Xdmx is a completely separate
X server. Thus, a separate config file format was developed. In addition, a
graphical configuration tool, xdmxconfig, was developed to allow the user to
create and arrange the screens in the configuration file. The -configfile and
-config command-line options can be used to start Xdmx using a configuration
file.

An extension that enables remote input testing is required for the X Test Suite
to function. During this phase, this extension (XTEST) was implemented in the
Xdmx server. The results from running the X Test Suite are described in detail
below.

X Test Suite

Introduction

The X Test Suite contains tests that verify Xlib functions operate correctly.
The test suite is designed to run on a single X server; however, since X
applications will not be able to tell the difference between the DMX server and
a standard X server, the X Test Suite should also run on the DMX server.

The Xdmx server was tested with the X Test Suite, and the existing failures are
noted in this section. To put these results in perspective, we first discuss
expected X Test failures and how errors in underlying systems can impact Xdmx
test results.

Expected Failures for a Single Head

A correctly implemented X server with a single screen is expected to fail
certain X Test tests. The following well-known errors occur because of rounding
error in the X server code:


XDrawArc: Tests 42, 63, 66, 73
XDrawArcs: Tests 45, 66, 69, 76
              

The following failures occur because of the high-level X server implementation:


XLoadQueryFont: Test 1
XListFontsWithInfo: Tests 3, 4
XQueryFont: Tests 1, 2
              

The following test fails when running the X server as root under Linux because
of the way directory modes are interpreted:


XWriteBitmapFile: Test 3
              

Depending on the video card used for the back-end, other failures may also
occur because of bugs in the low-level driver implementation. Over time,
failures of this kind are usually fixed by XFree86, but will show up in Xdmx
testing until then.

Expected Failures for Xinerama

Xinerama fails several X Test Suite tests because of design decisions made for
the current implementation of Xinerama. Over time, many of these errors will be
corrected by XFree86 and the group working on a new Xinerama implementation.
Therefore, Xdmx will also share X Suite Test failures with Xinerama.

We may be able to fix or work-around some of these failures at the Xdmx level,
but this will require additional exploration that was not part of Phase I.

Xinerama is constantly improving, and the list of Xinerama-related failures
depends on XFree86 version and the underlying graphics hardware. We tested with
a variety of hardware, including nVidia, S3, ATI Radeon, and Matrox G400 (in
dual-head mode). The list below includes only those failures that appear to be
from the Xinerama layer, and does not include failures listed in the previous
section, or failures that appear to be from the low-level graphics driver
itself:

These failures were noted with multiple Xinerama configurations:


XCopyPlane: Tests 13, 22, 31 (well-known Xinerama implementation issue)
XSetFontPath: Test 4
XGetDefault: Test 5
XMatchVisualInfo: Test 1
              

These failures were noted only when using one dual-head video card with a
4.2.99.x XFree86 server:


XListPixmapFormats: Test 1
XDrawRectangles: Test 45
              

These failures were noted only when using two video cards from different
vendors with a 4.1.99.x XFree86 server:


XChangeWindowAttributes: Test 32
XCreateWindow: Test 30
XDrawLine: Test 22
XFillArc: Test 22
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1
              

Additional Failures from Xdmx

When running Xdmx, no unexpected failures were noted. Since the Xdmx server is
based on Xinerama, we expect to have most of the Xinerama failures present in
the Xdmx server. Similarly, since the Xdmx server must rely on the low-level
device drivers on each back-end server, we also expect that Xdmx will exhibit
most of the back-end failures. Here is a summary:


XListPixmapFormats: Test 1 (configuration dependent)
XChangeWindowAttributes: Test 32
XCreateWindow: Test 30
XCopyPlane: Test 13, 22, 31
XSetFontPath: Test 4
XGetDefault: Test 5 (configuration dependent)
XMatchVisualInfo: Test 1
XRebindKeysym: Test 1 (configuration dependent)
                

Note that this list is shorter than the combined list for Xinerama because Xdmx
uses different code paths to perform some Xinerama operations. Further, some
Xinerama failures have been fixed in the XFree86 4.2.99.x CVS repository.

Summary and Future Work

Running the X Test Suite on Xdmx does not produce any failures that cannot be
accounted for by the underlying Xinerama subsystem used by the front-end or by
the low-level device-driver code running on the back-end X servers. The Xdmx
server therefore is as ``correct'' as possible with respect to the standard set
of X Test Suite tests.

During the following phases, we will continue to verify Xdmx correctness using
the X Test Suite. We may also use other tests suites or write additional tests
that run under the X Test Suite that specifically verify the expected behavior
of DMX.

Fonts

In Phase I, fonts are handled directly by both the front-end and the back-end
servers, which is required since we must treat each back-end server during this
phase as a ``black box''. What this requires is that the front- and back-end
servers must share the exact same font path. There are two ways to help make
sure that all servers share the same font path:

 1. First, each server can be configured to use the same font server. The font
    server, xfs, can be configured to serve fonts to multiple X servers via
    TCP.

 2. Second, each server can be configured to use the same font path and either
    those font paths can be copied to each back-end machine or they can be
    mounted (e.g., via NFS) on each back-end machine.

One additional concern is that a client program can set its own font path, and
if it does so, then that font path must be available on each back-end machine.

The -fontpath command line option was added to allow users to initialize the
font path of the front end server. This font path is propagated to each
back-end server when the default font is loaded. If there are any problems, an
error message is printed, which will describe the problem and list the current
font path. For more information about setting the font path, see the -fontpath
option description in the man page.

Performance

Phase I of development was not intended to optimize performance. Its focus was
on completely and correctly handling the base X11 protocol in the Xdmx server.
However, several insights were gained during Phase I, which are listed here for
reference during the next phase of development.

 1. Calls to XSync() can slow down rendering since it requires a complete round
    trip to and from a back-end server. This is especially problematic when
    communicating over long haul networks.

 2. Sending drawing requests to only the screens that they overlap should
    improve performance.

Pixmaps

Pixmaps were originally expected to be handled entirely in the front-end X
server; however, it was found that this overly complicated the rendering code
and would have required sending potentially large images to each back server
that required them when copying from pixmap to screen. Thus, pixmap state is
mirrored in the back-end server just as it is with regular window state. With
this implementation, the same rendering code that draws to windows can be used
to draw to pixmaps on the back-end server, and no large image transfers are
required to copy from pixmap to window.

Phase II

The second phase of development concentrates on performance optimizations.
These optimizations are documented here, with x11perf data to show how the
optimizations improve performance.

All benchmarks were performed by running Xdmx on a dual processor 1.4GHz AMD
Athlon machine with 1GB of RAM connecting over 100baseT to two single-processor
1GHz Pentium III machines with 256MB of RAM and ATI Rage 128 (RF) video cards.
The front end was running Linux 2.4.20-pre1-ac1 and the back ends were running
Linux 2.4.7-10 and version 4.2.99.1 of XFree86 pulled from the XFree86 CVS
repository on August 7, 2002. All systems were running Red Hat Linux 7.2.

Moving from XFree86 4.1.99.1 to 4.2.0.0

For phase II, the working source tree was moved to the branch tagged with
dmx-1-0-branch and was updated from version 4.1.99.1 (20 August 2001) of the
XFree86 sources to version 4.2.0.0 (18 January 2002). After this update, the
following tests were noted to be more than 10% faster:

1.13   Fill 300x300 opaque stippled trapezoid (161x145 stipple)
1.16   Fill 1x1 tiled trapezoid (161x145 tile)
1.13   Fill 10x10 tiled trapezoid (161x145 tile)
1.17   Fill 100x100 tiled trapezoid (161x145 tile)
1.16   Fill 1x1 tiled trapezoid (216x208 tile)
1.20   Fill 10x10 tiled trapezoid (216x208 tile)
1.15   Fill 100x100 tiled trapezoid (216x208 tile)
1.37   Circulate Unmapped window (200 kids)

And the following tests were noted to be more than 10% slower:

0.88   Unmap window via parent (25 kids)
0.75   Circulate Unmapped window (4 kids)
0.79   Circulate Unmapped window (16 kids)
0.80   Circulate Unmapped window (25 kids)
0.82   Circulate Unmapped window (50 kids)
0.85   Circulate Unmapped window (75 kids)

These changes were not caused by any changes in the DMX system, and may point
to changes in the XFree86 tree or to tests that have more "jitter" than most
other x11perf tests.

Global changes

During the development of the Phase II DMX server, several global changes were
made. These changes were also compared with the Phase I server. The following
tests were noted to be more than 10% faster:

1.13   Fill 300x300 opaque stippled trapezoid (161x145 stipple)
1.15   Fill 1x1 tiled trapezoid (161x145 tile)
1.13   Fill 10x10 tiled trapezoid (161x145 tile)
1.17   Fill 100x100 tiled trapezoid (161x145 tile)
1.16   Fill 1x1 tiled trapezoid (216x208 tile)
1.19   Fill 10x10 tiled trapezoid (216x208 tile)
1.15   Fill 100x100 tiled trapezoid (216x208 tile)
1.15   Circulate Unmapped window (4 kids)

The following tests were noted to be more than 10% slower:

0.69   Scroll 10x10 pixels
0.68   Scroll 100x100 pixels
0.68   Copy 10x10 from window to window
0.68   Copy 100x100 from window to window
0.76   Circulate Unmapped window (75 kids)
0.83   Circulate Unmapped window (100 kids)

For the remainder of this analysis, the baseline of comparison will be the
Phase II deliverable with all optimizations disabled (unless otherwise noted).
This will highlight how the optimizations in isolation impact performance.

XSync() Batching

During the Phase I implementation, XSync() was called after every protocol
request made by the DMX server. This provided the DMX server with an
interactive feel, but defeated X11's protocol buffering system and introduced
round-trip wire latency into every operation. During Phase II, DMX was changed
so that protocol requests are no longer followed by calls to XSync(). Instead,
the need for an XSync() is noted, and XSync() calls are only made every 100mS
or when the DMX server specifically needs to make a call to guarantee
interactivity. With this new system, X11 buffers protocol as much as possible
during a 100mS interval, and many unnecessary XSync() calls are avoided.

Out of more than 300 x11perf tests, 8 tests became more than 100 times faster,
with 68 more than 50X faster, 114 more than 10X faster, and 181 more than 2X
faster. See table below for summary.

The following tests were noted to be more than 10% slower with XSync() batching
on:

0.88   500x500 tiled rectangle (161x145 tile)
0.89   Copy 500x500 from window to window

Offscreen Optimization

Windows span one or more of the back-end servers' screens; however, during
Phase I development, windows were created on every back-end server and every
rendering request was sent to every window regardless of whether or not that
window was visible. With the offscreen optimization, the DMX server tracks when
a window is completely off of a back-end server's screen and, in that case, it
does not send rendering requests to those back-end windows. This optimization
saves bandwidth between the front and back-end servers, and it reduces the
number of XSync() calls. The performance tests were run on a DMX system with
only two back-end servers. Greater performance gains will be had as the number
of back-end servers increases.

Out of more than 300 x11perf tests, 3 tests were at least twice as fast, and
146 tests were at least 10% faster. Two tests were more than 10% slower with
the offscreen optimization:

0.88   Hide/expose window via popup (4 kids)
0.89   Resize unmapped window (75 kids)

Lazy Window Creation Optimization

As mentioned above, during Phase I, windows were created on every back-end
server even if they were not visible on that back-end. With the lazy window
creation optimization, the DMX server does not create windows on a back-end
server until they are either visible or they become the parents of a visible
window. This optimization builds on the offscreen optimization (described
above) and requires it to be enabled.

The lazy window creation optimization works by creating the window data
structures in the front-end server when a client creates a window, but delays
creation of the window on the back-end server(s). A private window structure in
the DMX server saves the relevant window data and tracks changes to the
window's attributes and stacking order for later use. The only times a window
is created on a back-end server are (1) when it is mapped and is at least
partially overlapping the back-end server's screen (tracked by the offscreen
optimization), or (2) when the window becomes the parent of a previously
visible window. The first case occurs when a window is mapped or when a visible
window is copied, moved or resized and now overlaps the back-end server's
screen. The second case occurs when starting a window manager after having
created windows to which the window manager needs to add decorations.

When either case occurs, a window on the back-end server is created using the
data saved in the DMX server's window private data structure. The stacking
order is then adjusted to correctly place the window on the back-end and lastly
the window is mapped. From this time forward, the window is handled exactly as
if the window had been created at the time of the client's request.

Note that when a window is no longer visible on a back-end server's screen
(e.g., it is moved offscreen), the window is not destroyed; rather, it is kept
and reused later if the window once again becomes visible on the back-end
server's screen. Originally with this optimization, destroying windows was
implemented but was later rejected because it increased bandwidth when windows
were opaquely moved or resized, which is common in many window managers.

The performance tests were run on a DMX system with only two back-end servers.
Greater performance gains will be had as the number of back-end servers
increases.

This optimization improved the following x11perf tests by more than 10%:

1.10   500x500 rectangle outline
1.12   Fill 100x100 stippled trapezoid (161x145 stipple)
1.20   Circulate Unmapped window (50 kids)
1.19   Circulate Unmapped window (75 kids)

Subdividing Rendering Primitives

X11 imaging requests transfer significant data between the client and the X
server. During Phase I, the DMX server would then transfer the image data to
each back-end server. Even with the offscreen optimization (above), these
requests still required transferring significant data to each back-end server
that contained a visible portion of the window. For example, if the client uses
XPutImage() to copy an image to a window that overlaps the entire DMX screen,
then the entire image is copied by the DMX server to every back-end server.

To reduce the amount of data transferred between the DMX server and the
back-end servers when XPutImage() is called, the image data is subdivided and
only the data that will be visible on a back-end server's screen is sent to
that back-end server. Xinerama already implements a subdivision algorithm for
XGetImage() and no further optimization was needed.

Other rendering primitives were analyzed, but the time required to subdivide
these primitives was a significant proportion of the time required to send the
entire rendering request to the back-end server, so this optimization was
rejected for the other rendering primitives.

Again, the performance tests were run on a DMX system with only two back-end
servers. Greater performance gains will be had as the number of back-end
servers increases.

This optimization improved the following x11perf tests by more than 10%:

1.12   Fill 100x100 stippled trapezoid (161x145 stipple)
1.26   PutImage 10x10 square
1.83   PutImage 100x100 square
1.91   PutImage 500x500 square
1.40   PutImage XY 10x10 square
1.48   PutImage XY 100x100 square
1.50   PutImage XY 500x500 square
1.45   Circulate Unmapped window (75 kids)
1.74   Circulate Unmapped window (100 kids)

The following test was noted to be more than 10% slower with this optimization:

0.88   10-pixel fill chord partial circle

Summary of x11perf Data

With all of the optimizations on, 53 x11perf tests are more than 100X faster
than the unoptimized Phase II deliverable, with 69 more than 50X faster, 73
more than 10X faster, and 199 more than twice as fast. No tests were more than
10% slower than the unoptimized Phase II deliverable. (Compared with the Phase
I deliverable, only Circulate Unmapped window (100 kids) was more than 10%
slower than the Phase II deliverable. As noted above, this test seems to have
wider variability than other x11perf tests.)

The following table summarizes relative x11perf test changes for all
optimizations individually and collectively. Note that some of the
optimizations have a synergistic effect when used together.


1: XSync() batching only
2: Off screen optimizations only
3: Window optimizations only
4: Subdivprims only
5: All optimizations

    1     2    3    4      5 Operation
------ ---- ---- ---- ------ ---------
  2.14 1.85 1.00 1.00   4.13 Dot
  1.67 1.80 1.00 1.00   3.31 1x1 rectangle
  2.38 1.43 1.00 1.00   2.44 10x10 rectangle
  1.00 1.00 0.92 0.98   1.00 100x100 rectangle
  1.00 1.00 1.00 1.00   1.00 500x500 rectangle
  1.83 1.85 1.05 1.06   3.54 1x1 stippled rectangle (8x8 stipple)
  2.43 1.43 1.00 1.00   2.41 10x10 stippled rectangle (8x8 stipple)
  0.98 1.00 1.00 1.00   1.00 100x100 stippled rectangle (8x8 stipple)
  1.00 1.00 1.00 1.00   0.98 500x500 stippled rectangle (8x8 stipple)
  1.75 1.75 1.00 1.00   3.40 1x1 opaque stippled rectangle (8x8 stipple)
  2.38 1.42 1.00 1.00   2.34 10x10 opaque stippled rectangle (8x8 stipple)
  1.00 1.00 0.97 0.97   1.00 100x100 opaque stippled rectangle (8x8 stipple)
  1.00 1.00 1.00 1.00   0.99 500x500 opaque stippled rectangle (8x8 stipple)
  1.82 1.82 1.04 1.04   3.56 1x1 tiled rectangle (4x4 tile)
  2.33 1.42 1.00 1.00   2.37 10x10 tiled rectangle (4x4 tile)
  1.00 0.92 1.00 1.00   1.00 100x100 tiled rectangle (4x4 tile)
  1.00 1.00 1.00 1.00   1.00 500x500 tiled rectangle (4x4 tile)
  1.94 1.62 1.00 1.00   3.66 1x1 stippled rectangle (17x15 stipple)
  1.74 1.28 1.00 1.00   1.73 10x10 stippled rectangle (17x15 stipple)
  1.00 1.00 1.00 0.89   0.98 100x100 stippled rectangle (17x15 stipple)
  1.00 1.00 1.00 1.00   0.98 500x500 stippled rectangle (17x15 stipple)
  1.94 1.62 1.00 1.00   3.67 1x1 opaque stippled rectangle (17x15 stipple)
  1.69 1.26 1.00 1.00   1.66 10x10 opaque stippled rectangle (17x15 stipple)
  1.00 0.95 1.00 1.00   1.00 100x100 opaque stippled rectangle (17x15 stipple)
  1.00 1.00 1.00 1.00   0.97 500x500 opaque stippled rectangle (17x15 stipple)
  1.93 1.61 0.99 0.99   3.69 1x1 tiled rectangle (17x15 tile)
  1.73 1.27 1.00 1.00   1.72 10x10 tiled rectangle (17x15 tile)
  1.00 1.00 1.00 1.00   0.98 100x100 tiled rectangle (17x15 tile)
  1.00 1.00 0.97 0.97   1.00 500x500 tiled rectangle (17x15 tile)
  1.95 1.63 1.00 1.00   3.83 1x1 stippled rectangle (161x145 stipple)
  1.80 1.30 1.00 1.00   1.83 10x10 stippled rectangle (161x145 stipple)
  0.97 1.00 1.00 1.00   1.01 100x100 stippled rectangle (161x145 stipple)
  1.00 1.00 1.00 1.00   0.98 500x500 stippled rectangle (161x145 stipple)
  1.95 1.63 1.00 1.00   3.56 1x1 opaque stippled rectangle (161x145 stipple)
  1.65 1.25 1.00 1.00   1.68 10x10 opaque stippled rectangle (161x145 stipple)
  1.00 1.00 1.00 1.00   1.01 100x100 opaque stippled rectangle (161x145...
  1.00 1.00 1.00 1.00   0.97 500x500 opaque stippled rectangle (161x145...
  1.95 1.63 0.98 0.99   3.80 1x1 tiled rectangle (161x145 tile)
  1.67 1.26 1.00 1.00   1.67 10x10 tiled rectangle (161x145 tile)
  1.13 1.14 1.14 1.14   1.14 100x100 tiled rectangle (161x145 tile)
  0.88 1.00 1.00 1.00   0.99 500x500 tiled rectangle (161x145 tile)
  1.93 1.63 1.00 1.00   3.53 1x1 tiled rectangle (216x208 tile)
  1.69 1.26 1.00 1.00   1.66 10x10 tiled rectangle (216x208 tile)
  1.00 1.00 1.00 1.00   1.00 100x100 tiled rectangle (216x208 tile)
  1.00 1.00 1.00 1.00   1.00 500x500 tiled rectangle (216x208 tile)
  1.82 1.70 1.00 1.00   3.38 1-pixel line segment
  2.07 1.56 0.90 1.00   3.31 10-pixel line segment
  1.29 1.10 1.00 1.00   1.27 100-pixel line segment
  1.05 1.06 1.03 1.03   1.09 500-pixel line segment
  1.30 1.13 1.00 1.00   1.29 100-pixel line segment (1 kid)
  1.32 1.15 1.00 1.00   1.32 100-pixel line segment (2 kids)
  1.33 1.16 1.00 1.00   1.33 100-pixel line segment (3 kids)
  1.92 1.64 1.00 1.00   3.73 10-pixel dashed segment
  1.34 1.16 1.00 1.00   1.34 100-pixel dashed segment
  1.24 1.11 0.99 0.97   1.23 100-pixel double-dashed segment
  1.72 1.77 1.00 1.00   3.25 10-pixel horizontal line segment
  1.83 1.66 1.01 1.00   3.54 100-pixel horizontal line segment
  1.86 1.30 1.00 1.00   1.84 500-pixel horizontal line segment
  2.11 1.52 1.00 0.99   3.02 10-pixel vertical line segment
  1.21 1.10 1.00 1.00   1.20 100-pixel vertical line segment
  1.03 1.03 1.00 1.00   1.02 500-pixel vertical line segment
  4.42 1.68 1.00 1.01   4.64 10x1 wide horizontal line segment
  1.83 1.31 1.00 1.00   1.83 100x10 wide horizontal line segment
  1.07 1.00 0.96 1.00   1.07 500x50 wide horizontal line segment
  4.10 1.67 1.00 1.00   4.62 10x1 wide vertical line segment
  1.50 1.24 1.06 1.06   1.48 100x10 wide vertical line segment
  1.06 1.03 1.00 1.00   1.05 500x50 wide vertical line segment
  2.54 1.61 1.00 1.00   3.61 1-pixel line
  2.71 1.48 1.00 1.00   2.67 10-pixel line
  1.19 1.09 1.00 1.00   1.19 100-pixel line
  1.04 1.02 1.00 1.00   1.03 500-pixel line
  2.68 1.51 0.98 1.00   3.17 10-pixel dashed line
  1.23 1.11 0.99 0.99   1.23 100-pixel dashed line
  1.15 1.08 1.00 1.00   1.15 100-pixel double-dashed line
  2.27 1.39 1.00 1.00   2.23 10x1 wide line
  1.20 1.09 1.00 1.00   1.20 100x10 wide line
  1.04 1.02 1.00 1.00   1.04 500x50 wide line
  1.52 1.45 1.00 1.00   1.52 100x10 wide dashed line
  1.54 1.47 1.00 1.00   1.54 100x10 wide double-dashed line
  1.97 1.30 0.96 0.95   1.95 10x10 rectangle outline
  1.44 1.27 1.00 1.00   1.43 100x100 rectangle outline
  3.22 2.16 1.10 1.09   3.61 500x500 rectangle outline
  1.95 1.34 1.00 1.00   1.90 10x10 wide rectangle outline
  1.14 1.14 1.00 1.00   1.13 100x100 wide rectangle outline
  1.00 1.00 1.00 1.00   1.00 500x500 wide rectangle outline
  1.57 1.72 1.00 1.00   3.03 1-pixel circle
  1.96 1.35 1.00 1.00   1.92 10-pixel circle
  1.21 1.07 0.86 0.97   1.20 100-pixel circle
  1.08 1.04 1.00 1.00   1.08 500-pixel circle
  1.39 1.19 1.03 1.03   1.38 100-pixel dashed circle
  1.21 1.11 1.00 1.00   1.23 100-pixel double-dashed circle
  1.59 1.28 1.00 1.00   1.58 10-pixel wide circle
  1.22 1.12 0.99 1.00   1.22 100-pixel wide circle
  1.06 1.04 1.00 1.00   1.05 500-pixel wide circle
  1.87 1.84 1.00 1.00   1.85 100-pixel wide dashed circle
  1.90 1.93 1.01 1.01   1.90 100-pixel wide double-dashed circle
  2.13 1.43 1.00 1.00   2.32 10-pixel partial circle
  1.42 1.18 1.00 1.00   1.42 100-pixel partial circle
  1.92 1.85 1.01 1.01   1.89 10-pixel wide partial circle
  1.73 1.67 1.00 1.00   1.73 100-pixel wide partial circle
  1.36 1.95 1.00 1.00   2.64 1-pixel solid circle
  2.02 1.37 1.00 1.00   2.03 10-pixel solid circle
  1.19 1.09 1.00 1.00   1.19 100-pixel solid circle
  1.02 0.99 1.00 1.00   1.01 500-pixel solid circle
  1.74 1.28 1.00 0.88   1.73 10-pixel fill chord partial circle
  1.31 1.13 1.00 1.00   1.31 100-pixel fill chord partial circle
  1.67 1.31 1.03 1.03   1.72 10-pixel fill slice partial circle
  1.30 1.13 1.00 1.00   1.28 100-pixel fill slice partial circle
  2.45 1.49 1.01 1.00   2.71 10-pixel ellipse
  1.22 1.10 1.00 1.00   1.22 100-pixel ellipse
  1.09 1.04 1.00 1.00   1.09 500-pixel ellipse
  1.90 1.28 1.00 1.00   1.89 100-pixel dashed ellipse
  1.62 1.24 0.96 0.97   1.61 100-pixel double-dashed ellipse
  2.43 1.50 1.00 1.00   2.42 10-pixel wide ellipse
  1.61 1.28 1.03 1.03   1.60 100-pixel wide ellipse
  1.08 1.05 1.00 1.00   1.08 500-pixel wide ellipse
  1.93 1.88 1.00 1.00   1.88 100-pixel wide dashed ellipse
  1.94 1.89 1.01 1.00   1.94 100-pixel wide double-dashed ellipse
  2.31 1.48 1.00 1.00   2.67 10-pixel partial ellipse
  1.38 1.17 1.00 1.00   1.38 100-pixel partial ellipse
  2.00 1.85 0.98 0.97   1.98 10-pixel wide partial ellipse
  1.89 1.86 1.00 1.00   1.89 100-pixel wide partial ellipse
  3.49 1.60 1.00 1.00   3.65 10-pixel filled ellipse
  1.67 1.26 1.00 1.00   1.67 100-pixel filled ellipse
  1.06 1.04 1.00 1.00   1.06 500-pixel filled ellipse
  2.38 1.43 1.01 1.00   2.32 10-pixel fill chord partial ellipse
  2.06 1.30 1.00 1.00   2.05 100-pixel fill chord partial ellipse
  2.27 1.41 1.00 1.00   2.27 10-pixel fill slice partial ellipse
  1.98 1.33 1.00 0.97   1.97 100-pixel fill slice partial ellipse
 57.46 1.99 1.01 1.00 114.92 Fill 1x1 equivalent triangle
 56.94 1.98 1.01 1.00  73.89 Fill 10x10 equivalent triangle
  6.07 1.75 1.00 1.00   6.07 Fill 100x100 equivalent triangle
 51.12 1.98 1.00 1.00 102.81 Fill 1x1 trapezoid
 51.42 1.82 1.01 1.00  94.89 Fill 10x10 trapezoid
  6.47 1.80 1.00 1.00   6.44 Fill 100x100 trapezoid
  1.56 1.28 1.00 0.99   1.56 Fill 300x300 trapezoid
 51.27 1.97 0.96 0.97 102.54 Fill 1x1 stippled trapezoid (8x8 stipple)
 51.73 2.00 1.02 1.02  67.92 Fill 10x10 stippled trapezoid (8x8 stipple)
  5.36 1.72 1.00 1.00   5.36 Fill 100x100 stippled trapezoid (8x8 stipple)
  1.54 1.26 1.00 1.00   1.59 Fill 300x300 stippled trapezoid (8x8 stipple)
 51.41 1.94 1.01 1.00 102.82 Fill 1x1 opaque stippled trapezoid (8x8 stipple)
 50.71 1.95 0.99 1.00  65.44 Fill 10x10 opaque stippled trapezoid (8x8...
  5.33 1.73 1.00 1.00   5.36 Fill 100x100 opaque stippled trapezoid (8x8...
  1.58 1.25 1.00 1.00   1.58 Fill 300x300 opaque stippled trapezoid (8x8...
 51.56 1.96 0.99 0.90 103.68 Fill 1x1 tiled trapezoid (4x4 tile)
 51.59 1.99 1.01 1.01  62.25 Fill 10x10 tiled trapezoid (4x4 tile)
  5.38 1.72 1.00 1.00   5.38 Fill 100x100 tiled trapezoid (4x4 tile)
  1.54 1.25 1.00 0.99   1.58 Fill 300x300 tiled trapezoid (4x4 tile)
 51.70 1.98 1.01 1.01 103.98 Fill 1x1 stippled trapezoid (17x15 stipple)
 44.86 1.97 1.00 1.00  44.86 Fill 10x10 stippled trapezoid (17x15 stipple)
  2.74 1.56 1.00 1.00   2.73 Fill 100x100 stippled trapezoid (17x15 stipple)
  1.29 1.14 1.00 1.00   1.27 Fill 300x300 stippled trapezoid (17x15 stipple)
 51.41 1.96 0.96 0.95 103.39 Fill 1x1 opaque stippled trapezoid (17x15...
 45.14 1.96 1.01 1.00  45.14 Fill 10x10 opaque stippled trapezoid (17x15...
  2.68 1.56 1.00 1.00   2.68 Fill 100x100 opaque stippled trapezoid (17x15...
  1.26 1.10 1.00 1.00   1.28 Fill 300x300 opaque stippled trapezoid (17x15...
 51.13 1.97 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (17x15 tile)
 47.58 1.96 1.00 1.00  47.86 Fill 10x10 tiled trapezoid (17x15 tile)
  2.74 1.56 1.00 1.00   2.74 Fill 100x100 tiled trapezoid (17x15 tile)
  1.29 1.14 1.00 1.00   1.28 Fill 300x300 tiled trapezoid (17x15 tile)
 51.13 1.97 0.99 0.97 103.39 Fill 1x1 stippled trapezoid (161x145 stipple)
 45.14 1.97 1.00 1.00  44.29 Fill 10x10 stippled trapezoid (161x145 stipple)
  3.02 1.77 1.12 1.12   3.38 Fill 100x100 stippled trapezoid (161x145 stipple)
  1.31 1.13 1.00 1.00   1.30 Fill 300x300 stippled trapezoid (161x145 stipple)
 51.27 1.97 1.00 1.00 103.10 Fill 1x1 opaque stippled trapezoid (161x145...
 45.01 1.97 1.00 1.00  45.01 Fill 10x10 opaque stippled trapezoid (161x145...
  2.67 1.56 1.00 1.00   2.69 Fill 100x100 opaque stippled trapezoid (161x145..
  1.29 1.13 1.00 1.01   1.27 Fill 300x300 opaque stippled trapezoid (161x145..
 51.41 1.96 1.00 0.99 103.39 Fill 1x1 tiled trapezoid (161x145 tile)
 45.01 1.96 0.98 1.00  45.01 Fill 10x10 tiled trapezoid (161x145 tile)
  2.62 1.36 1.00 1.00   2.69 Fill 100x100 tiled trapezoid (161x145 tile)
  1.27 1.13 1.00 1.00   1.22 Fill 300x300 tiled trapezoid (161x145 tile)
 51.13 1.98 1.00 1.00 103.39 Fill 1x1 tiled trapezoid (216x208 tile)
 45.14 1.97 1.01 0.99  45.14 Fill 10x10 tiled trapezoid (216x208 tile)
  2.62 1.55 1.00 1.00   2.71 Fill 100x100 tiled trapezoid (216x208 tile)
  1.28 1.13 1.00 1.00   1.20 Fill 300x300 tiled trapezoid (216x208 tile)
 50.71 1.95 1.00 1.00  54.70 Fill 10x10 equivalent complex polygon
  5.51 1.71 0.96 0.98   5.47 Fill 100x100 equivalent complex polygons
  8.39 1.97 1.00 1.00  16.75 Fill 10x10 64-gon (Convex)
  8.38 1.83 1.00 1.00   8.43 Fill 100x100 64-gon (Convex)
  8.50 1.96 1.00 1.00  16.64 Fill 10x10 64-gon (Complex)
  8.26 1.83 1.00 1.00   8.35 Fill 100x100 64-gon (Complex)
 14.09 1.87 1.00 1.00  14.05 Char in 80-char line (6x13)
 11.91 1.87 1.00 1.00  11.95 Char in 70-char line (8x13)
 11.16 1.85 1.01 1.00  11.10 Char in 60-char line (9x15)
 10.09 1.78 1.00 1.00  10.09 Char16 in 40-char line (k14)
  6.15 1.75 1.00 1.00   6.31 Char16 in 23-char line (k24)
 11.92 1.90 1.03 1.03  11.88 Char in 80-char line (TR 10)
  8.18 1.78 1.00 0.99   8.17 Char in 30-char line (TR 24)
 42.83 1.44 1.01 1.00  42.11 Char in 20/40/20 line (6x13, TR 10)
 27.45 1.43 1.01 1.01  27.45 Char16 in 7/14/7 line (k14, k24)
 12.13 1.85 1.00 1.00  12.05 Char in 80-char image line (6x13)
 10.00 1.84 1.00 1.00  10.00 Char in 70-char image line (8x13)
  9.18 1.83 1.00 1.00   9.12 Char in 60-char image line (9x15)
  9.66 1.82 0.98 0.95   9.66 Char16 in 40-char image line (k14)
  5.82 1.72 1.00 1.00   5.99 Char16 in 23-char image line (k24)
  8.70 1.80 1.00 1.00   8.65 Char in 80-char image line (TR 10)
  4.67 1.66 1.00 1.00   4.67 Char in 30-char image line (TR 24)
 84.43 1.47 1.00 1.00 124.18 Scroll 10x10 pixels
  3.73 1.50 1.00 0.98   3.73 Scroll 100x100 pixels
  1.00 1.00 1.00 1.00   1.00 Scroll 500x500 pixels
 84.43 1.51 1.00 1.00 134.02 Copy 10x10 from window to window
  3.62 1.51 0.98 0.98   3.62 Copy 100x100 from window to window
  0.89 1.00 1.00 1.00   1.00 Copy 500x500 from window to window
 57.06 1.99 1.00 1.00  88.64 Copy 10x10 from pixmap to window
  2.49 2.00 1.00 1.00   2.48 Copy 100x100 from pixmap to window
  1.00 0.91 1.00 1.00   0.98 Copy 500x500 from pixmap to window
  2.04 1.01 1.00 1.00   2.03 Copy 10x10 from window to pixmap
  1.05 1.00 1.00 1.00   1.05 Copy 100x100 from window to pixmap
  1.00 1.00 0.93 1.00   1.04 Copy 500x500 from window to pixmap
 58.52 1.03 1.03 1.02  57.95 Copy 10x10 from pixmap to pixmap
  2.40 1.00 1.00 1.00   2.45 Copy 100x100 from pixmap to pixmap
  1.00 1.00 1.00 1.00   1.00 Copy 500x500 from pixmap to pixmap
 51.57 1.92 1.00 1.00  85.75 Copy 10x10 1-bit deep plane
  6.37 1.75 1.01 1.01   6.37 Copy 100x100 1-bit deep plane
  1.26 1.11 1.00 1.00   1.24 Copy 500x500 1-bit deep plane
  4.23 1.63 0.98 0.97   4.38 Copy 10x10 n-bit deep plane
  1.04 1.02 1.00 1.00   1.04 Copy 100x100 n-bit deep plane
  1.00 1.00 1.00 1.00   1.00 Copy 500x500 n-bit deep plane
  6.45 1.98 1.00 1.26  12.80 PutImage 10x10 square
  1.10 1.87 1.00 1.83   2.11 PutImage 100x100 square
  1.02 1.93 1.00 1.91   1.91 PutImage 500x500 square
  4.17 1.78 1.00 1.40   7.18 PutImage XY 10x10 square
  1.27 1.49 0.97 1.48   2.10 PutImage XY 100x100 square
  1.00 1.50 1.00 1.50   1.52 PutImage XY 500x500 square
  1.07 1.01 1.00 1.00   1.06 GetImage 10x10 square
  1.01 1.00 1.00 1.00   1.01 GetImage 100x100 square
  1.00 1.00 1.00 1.00   1.00 GetImage 500x500 square
  1.56 1.00 0.99 0.97   1.56 GetImage XY 10x10 square
  1.02 1.00 1.00 1.00   1.02 GetImage XY 100x100 square
  1.00 1.00 1.00 1.00   1.00 GetImage XY 500x500 square
  1.00 1.00 1.01 0.98   0.95 X protocol NoOperation
  1.02 1.03 1.04 1.03   1.00 QueryPointer
  1.03 1.02 1.04 1.03   1.00 GetProperty
100.41 1.51 1.00 1.00 198.76 Change graphics context
 45.81 1.00 0.99 0.97  57.10 Create and map subwindows (4 kids)
 78.45 1.01 1.02 1.02  63.07 Create and map subwindows (16 kids)
 73.91 1.01 1.00 1.00  56.37 Create and map subwindows (25 kids)
 73.22 1.00 1.00 1.00  49.07 Create and map subwindows (50 kids)
 72.36 1.01 0.99 1.00  32.14 Create and map subwindows (75 kids)
 70.34 1.00 1.00 1.00  30.12 Create and map subwindows (100 kids)
 55.00 1.00 1.00 0.99  23.75 Create and map subwindows (200 kids)
 55.30 1.01 1.00 1.00 141.03 Create unmapped window (4 kids)
 55.38 1.01 1.01 1.00 163.25 Create unmapped window (16 kids)
 54.75 0.96 1.00 0.99 166.95 Create unmapped window (25 kids)
 54.83 1.00 1.00 0.99 178.81 Create unmapped window (50 kids)
 55.38 1.01 1.01 1.00 181.20 Create unmapped window (75 kids)
 55.38 1.01 1.01 1.00 181.20 Create unmapped window (100 kids)
 54.87 1.01 1.01 1.00 182.05 Create unmapped window (200 kids)
 28.13 1.00 1.00 1.00  30.75 Map window via parent (4 kids)
 36.14 1.01 1.01 1.01  32.58 Map window via parent (16 kids)
 26.13 1.00 0.98 0.95  29.85 Map window via parent (25 kids)
 40.07 1.00 1.01 1.00  27.57 Map window via parent (50 kids)
 23.26 0.99 1.00 1.00  18.23 Map window via parent (75 kids)
 22.91 0.99 1.00 0.99  16.52 Map window via parent (100 kids)
 27.79 1.00 1.00 0.99  12.50 Map window via parent (200 kids)
 22.35 1.00 1.00 1.00  56.19 Unmap window via parent (4 kids)
  9.57 1.00 0.99 1.00  89.78 Unmap window via parent (16 kids)
 80.77 1.01 1.00 1.00 103.85 Unmap window via parent (25 kids)
 96.34 1.00 1.00 1.00 116.06 Unmap window via parent (50 kids)
 99.72 1.00 1.00 1.00 124.93 Unmap window via parent (75 kids)
112.36 1.00 1.00 1.00 125.27 Unmap window via parent (100 kids)
105.41 1.00 1.00 0.99 120.00 Unmap window via parent (200 kids)
 51.29 1.03 1.02 1.02  74.19 Destroy window via parent (4 kids)
 86.75 0.99 0.99 0.99 116.87 Destroy window via parent (16 kids)
106.43 1.01 1.01 1.01 127.49 Destroy window via parent (25 kids)
120.34 1.01 1.01 1.00 140.11 Destroy window via parent (50 kids)
126.67 1.00 0.99 0.99 145.00 Destroy window via parent (75 kids)
126.11 1.01 1.01 1.00 140.56 Destroy window via parent (100 kids)
128.57 1.01 1.00 1.00 137.91 Destroy window via parent (200 kids)
 16.04 0.88 1.00 1.00  20.36 Hide/expose window via popup (4 kids)
 19.04 1.01 1.00 1.00  23.48 Hide/expose window via popup (16 kids)
 19.22 1.00 1.00 1.00  20.44 Hide/expose window via popup (25 kids)
 17.41 1.00 0.91 0.97  17.68 Hide/expose window via popup (50 kids)
 17.29 1.01 1.00 1.01  17.07 Hide/expose window via popup (75 kids)
 16.74 1.00 1.00 1.00  16.17 Hide/expose window via popup (100 kids)
 10.30 1.00 1.00 1.00  10.51 Hide/expose window via popup (200 kids)
 16.48 1.01 1.00 1.00  26.05 Move window (4 kids)
 17.01 0.95 1.00 1.00  23.97 Move window (16 kids)
 16.95 1.00 1.00 1.00  22.90 Move window (25 kids)
 16.05 1.01 1.00 1.00  21.32 Move window (50 kids)
 15.58 1.00 0.98 0.98  19.44 Move window (75 kids)
 14.98 1.02 1.03 1.03  18.17 Move window (100 kids)
 10.90 1.01 1.01 1.00  12.68 Move window (200 kids)
 49.42 1.00 1.00 1.00 198.27 Moved unmapped window (4 kids)
 50.72 0.97 1.00 1.00 193.66 Moved unmapped window (16 kids)
 50.87 1.00 0.99 1.00 195.09 Moved unmapped window (25 kids)
 50.72 1.00 1.00 1.00 189.34 Moved unmapped window (50 kids)
 50.87 1.00 1.00 1.00 191.33 Moved unmapped window (75 kids)
 50.87 1.00 1.00 0.90 186.71 Moved unmapped window (100 kids)
 50.87 1.00 1.00 1.00 179.19 Moved unmapped window (200 kids)
 41.04 1.00 1.00 1.00  56.61 Move window via parent (4 kids)
 69.81 1.00 1.00 1.00 130.82 Move window via parent (16 kids)
 95.81 1.00 1.00 1.00 141.92 Move window via parent (25 kids)
 95.98 1.00 1.00 1.00 149.43 Move window via parent (50 kids)
 96.59 1.01 1.01 1.00 153.98 Move window via parent (75 kids)
 97.19 1.00 1.00 1.00 157.30 Move window via parent (100 kids)
 96.67 1.00 0.99 0.96 159.44 Move window via parent (200 kids)
 17.75 1.01 1.00 1.00  27.61 Resize window (4 kids)
 17.94 1.00 1.00 0.99  25.42 Resize window (16 kids)
 17.92 1.01 1.00 1.00  24.47 Resize window (25 kids)
 17.24 0.97 1.00 1.00  24.14 Resize window (50 kids)
 16.81 1.00 1.00 0.99  22.75 Resize window (75 kids)
 16.08 1.00 1.00 1.00  21.20 Resize window (100 kids)
 12.92 1.00 0.99 1.00  16.26 Resize window (200 kids)
 52.94 1.01 1.00 1.00 327.12 Resize unmapped window (4 kids)
 53.60 1.01 1.01 1.01 333.71 Resize unmapped window (16 kids)
 52.99 1.00 1.00 1.00 337.29 Resize unmapped window (25 kids)
 51.98 1.00 1.00 1.00 329.38 Resize unmapped window (50 kids)
 53.05 0.89 1.00 1.00 322.60 Resize unmapped window (75 kids)
 53.05 1.00 1.00 1.00 318.08 Resize unmapped window (100 kids)
 53.11 1.00 1.00 0.99 306.21 Resize unmapped window (200 kids)
 16.76 1.00 0.96 1.00  19.46 Circulate window (4 kids)
 17.24 1.00 1.00 0.97  16.24 Circulate window (16 kids)
 16.30 1.03 1.03 1.03  15.85 Circulate window (25 kids)
 13.45 1.00 1.00 1.00  14.90 Circulate window (50 kids)
 12.91 1.00 1.00 1.00  13.06 Circulate window (75 kids)
 11.30 0.98 1.00 1.00  11.03 Circulate window (100 kids)
  7.58 1.01 1.01 0.99   7.47 Circulate window (200 kids)
  1.01 1.01 0.98 1.00   0.95 Circulate Unmapped window (4 kids)
  1.07 1.07 1.01 1.07   1.02 Circulate Unmapped window (16 kids)
  1.04 1.09 1.06 1.05   0.97 Circulate Unmapped window (25 kids)
  1.04 1.23 1.20 1.18   1.05 Circulate Unmapped window (50 kids)
  1.18 1.53 1.19 1.45   1.24 Circulate Unmapped window (75 kids)
  1.08 1.02 1.01 1.74   1.01 Circulate Unmapped window (100 kids)
  1.01 1.12 0.98 0.91   0.97 Circulate Unmapped window (200 kids)

Profiling with OProfile

OProfile (available from http://oprofile.sourceforge.net/) is a system-wide
profiler for Linux systems that uses processor-level counters to collect
sampling data. OProfile can provide information that is similar to that
provided by gprof, but without the necessity of recompiling the program with
special instrumentation (i.e., OProfile can collect statistical profiling
information about optimized programs). A test harness was developed to collect
OProfile data for each x11perf test individually.

Test runs were performed using the RETIRED_INSNS counter on the AMD Athlon and
the CPU_CLK_HALTED counter on the Intel Pentium III (with a test configuration
different from the one described above). We have examined OProfile output and
have compared it with gprof output. This investigation has not produced results
that yield performance increases in x11perf numbers.

X Test Suite

The X Test Suite was run on the fully optimized DMX server using the
configuration described above. The following failures were noted:

XListPixmapFormats: Test 1              [1]
XChangeWindowAttributes: Test 32        [1]
XCreateWindow: Test 30                  [1]
XFreeColors: Test 4                     [3]
XCopyArea: Test 13, 17, 21, 25, 30      [2]
XCopyPlane: Test 11, 15, 27, 31         [2]
XSetFontPath: Test 4                    [1]
XChangeKeyboardControl: Test 9, 10      [1]

[1] Previously documented errors expected from the Xinerama
    implementation (see Phase I discussion).
[2] Newly noted errors that have been verified as expected
    behavior of the Xinerama implementation.
[3] Newly noted error that has been verified as a Xinerama
    implementation bug.

Phase III

During the third phase of development, support was provided for the following
extensions: SHAPE, RENDER, XKEYBOARD, XInput.

SHAPE

The SHAPE extension is supported. Test applications (e.g., xeyes and oclock)
and window managers that make use of the SHAPE extension will work as expected.

RENDER

The RENDER extension is supported. The version included in the DMX CVS tree is
version 0.2, and this version is fully supported by Xdmx. Applications using
only version 0.2 functions will work correctly; however, some apps that make
use of functions from later versions do not properly check the extension's
major/minor version numbers. These apps will fail with a Bad Implementation
error when using post-version 0.2 functions. This is expected behavior. When
the DMX CVS tree is updated to include newer versions of RENDER, support for
these newer functions will be added to the DMX X server.

XKEYBOARD

The XKEYBOARD extension is supported. If present on the back-end X servers, the
XKEYBOARD extension will be used to obtain information about the type of the
keyboard for initialization. Otherwise, the keyboard will be initialized using
defaults. Note that this departs from older behavior: when Xdmx is compiled
without XKEYBOARD support, the map from the back-end X server will be
preserved. With XKEYBOARD support, the map is not preserved because better
information and control of the keyboard is available.

XInput

The XInput extension is supported. Any device can be used as a core device and
be used as an XInput extension device, with the exception of core devices on
the back-end servers. This limitation is present because cursor handling on the
back-end requires that the back-end cursor sometimes track the Xdmx core cursor
-- behavior that is incompatible with using the back-end pointer as a non-core
device.

Currently, back-end extension devices are not available as Xdmx extension
devices, but this limitation should be removed in the future.

To demonstrate the XInput extension, and to provide more examples for low-level
input device driver writers, USB device drivers have been written for mice
(usb-mou), keyboards (usb-kbd), and non-mouse/non-keyboard USB devices
(usb-oth). Please see the man page for information on Linux kernel drivers that
are required for using these Xdmx drivers.

DPMS

The DPMS extension is exported but does not do anything at this time.

Other Extensions

The LBX, SECURITY, XC-APPGROUP, and XFree86-Bigfont extensions do not require
any special Xdmx support and have been exported.

The BIG-REQUESTS, DEC-XTRAP, DOUBLE-BUFFER, Extended-Visual-Information,
FontCache, GLX, MIT-SCREEN-SAVER, MIT-SHM, MIT-SUNDRY-NONSTANDARD, RECORD,
SECURITY, SGI-GLX, SYNC, TOG-CUP, X-Resource, XC-MISC, XFree86-DGA,
XFree86-DRI, XFree86-Misc, XFree86-VidModeExtension, and XVideo extensions are
not supported at this time, but will be evaluated for inclusion in future DMX
releases. See below for additional work on extensions after Phase III.

Phase IV

Moving to XFree86 4.3.0

For Phase IV, the recent release of XFree86 4.3.0 (27 February 2003) was merged
onto the dmx.sourceforge.net CVS trunk and all work is proceeding using this
tree.

Extensions

XC-MISC (supported)

XC-MISC is used internally by the X library to recycle XIDs from the X server.
This is important for long-running X server sessions. Xdmx supports this
extension. The X Test Suite passed and failed the exact same tests before and
after this extension was enabled.

Extended-Visual-Information (supported)

The Extended-Visual-Information extension provides a method for an X client to
obtain detailed visual information. Xdmx supports this extension. It was tested
using the hw/dmx/examples/evi example program. Note that this extension is not
Xinerama-aware -- it will return visual information for each screen even though
Xinerama is causing the X server to export a single logical screen.

RES (supported)

The X-Resource extension provides a mechanism for a client to obtain detailed
information about the resources used by other clients. This extension was
tested with the hw/dmx/examples/res program. The X Test Suite passed and failed
the exact same tests before and after this extension was enabled.

BIG-REQUESTS (supported)

This extension enables the X11 protocol to handle requests longer than 262140
bytes. The X Test Suite passed and failed the exact same tests before and after
this extension was enabled.

XSYNC (supported)

This extension provides facilities for two different X clients to synchronize
their requests. This extension was minimally tested with xdpyinfo and the X
Test Suite passed and failed the exact same tests before and after this
extension was enabled.

XTEST, RECORD, DEC-XTRAP (supported) and XTestExtension1 (not supported)

The XTEST and RECORD extension were developed by the X Consortium for use in
the X Test Suite and are supported as a standard in the X11R6 tree. They are
also supported in Xdmx. When X Test Suite tests that make use of the XTEST
extension are run, Xdmx passes and fails exactly the same tests as does a
standard XFree86 X server. When the rcrdtest test (a part of the X Test Suite
that verifies the RECORD extension) is run, Xdmx passes and fails exactly the
same tests as does a standard XFree86 X server.

There are two older XTEST-like extensions: DEC-XTRAP and XTestExtension1. The
XTestExtension1 extension was developed for use by the X Testing Consortium for
use with a test suite that eventually became (part of?) the X Test Suite.
Unlike XTEST, which only allows events to be sent to the server, the
XTestExtension1 extension also allowed events to be recorded (similar to the
RECORD extension). The second is the DEC-XTRAP extension that was developed by
the Digital Equipment Corporation.

The DEC-XTRAP extension is available from Xdmx and has been tested with the
xtrap* tools which are distributed as standard X11R6 clients.

The XTestExtension1 is not supported because it does not appear to be used by
any modern X clients (the few that support it also support XTEST) and because
there are no good methods available for testing that it functions correctly
(unlike XTEST and DEC-XTRAP, the code for XTestExtension1 is not part of the
standard X server source tree, so additional testing is important).

Most of these extensions are documented in the X11R6 source tree. Further,
several original papers exist that this author was unable to locate -- for
completeness and historical interest, citations are provide:

XRECORD         Martha Zimet. Extending X For Recording. 8th Annual X Technical
                Conference Boston, MA January 24-26, 1994.

DEC-XTRAP       Dick Annicchiarico, Robert Chesler, Alan Jamison. XTrap
                Architecture. Digital Equipment Corporation, July 1991.

XTestExtension1 Larry Woestman. X11 Input Synthesis Extension Proposal. Hewlett
                Packard, November 1991.

MIT-MISC (not supported)

The MIT-MISC extension is used to control a bug-compatibility flag that
provides compatibility with xterm programs from X11R1 and X11R2. There does not
appear to be a single client available that makes use of this extension and
there is not way to verify that it works correctly. The Xdmx server does not
support MIT-MISC.

SCREENSAVER (not supported)

This extension provides special support for the X screen saver. It was tested
with beforelight, which appears to be the only client that works with it. When
Xinerama was not active, beforelight behaved as expected. However, when
Xinerama was active, beforelight did not behave as expected. Further, when this
extension is not active, xscreensaver (a widely-used X screen saver program)
did not behave as expected. Since this extension is not Xinerama-aware and is
not commonly used with expected results by clients, we have left this extension
disabled at this time.

GLX (supported)

The GLX extension provides OpenGL and GLX windowing support. In Xdmx, the
extension is called glxProxy, and it is Xinerama aware. It works by either
feeding requests forward through Xdmx to each of the back-end servers or
handling them locally. All rendering requests are handled on the back-end X
servers. This code was donated to the DMX project by SGI. For the X Test Suite
results comparison, see below.

RENDER (supported)

The X Rendering Extension (RENDER) provides support for digital image
composition. Geometric and text rendering are supported. RENDER is partially
Xinerama-aware, with text and the most basic compositing operator; however, its
higher level primitives (triangles, triangle strips, and triangle fans) are not
yet Xinerama-aware. The RENDER extension is still under development, and is
currently at version 0.8. Additional support will be required in DMX as more
primitives and/or requests are added to the extension.

There is currently no test suite for the X Rendering Extension; however, there
has been discussion of developing a test suite as the extension matures. When
that test suite becomes available, additional testing can be performed with
Xdmx. The X Test Suite passed and failed the exact same tests before and after
this extension was enabled.

Summary

To summarize, the following extensions are currently supported: BIG-REQUESTS,
DEC-XTRAP, DMX, DPMS, Extended-Visual-Information, GLX, LBX, RECORD, RENDER,
SECURITY, SHAPE, SYNC, X-Resource, XC-APPGROUP, XC-MISC, XFree86-Bigfont,
XINERAMA, XInputExtension, XKEYBOARD, and XTEST.

The following extensions are not supported at this time: DOUBLE-BUFFER,
FontCache, MIT-SCREEN-SAVER, MIT-SHM, MIT-SUNDRY-NONSTANDARD, TOG-CUP,
XFree86-DGA, XFree86-Misc, XFree86-VidModeExtension, XTestExtensionExt1, and
XVideo.

Additional Testing with the X Test Suite

XFree86 without XTEST

After the release of XFree86 4.3.0, we retested the XFree86 X server with and
without using the XTEST extension. When the XTEST extension was not used for
testing, the XFree86 4.3.0 server running on our usual test system with a
Radeon VE card reported unexpected failures in the following tests:


XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XGetDefault: Test 5
XRebindKeysym: Test 1

XFree86 with XTEST

When using the XTEST extension, the XFree86 4.3.0 server reported the following
errors:


XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XGetDefault: Test 5
XRebindKeysym: Test 1

XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4

While these errors may be important, they will probably be fixed eventually in
the XFree86 source tree. We are particularly interested in demonstrating that
the Xdmx server does not introduce additional failures that are not known
Xinerama failures.

Xdmx with XTEST, without Xinerama, without GLX

Without Xinerama, but using the XTEST extension, the following errors were
reported from Xdmx (note that these are the same as for the XFree86 4.3.0,
except that XGetDefault no longer fails):


XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1

XAllowEvents: Tests  20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4

Xdmx with XTEST, with Xinerama, without GLX

With Xinerama, using the XTEST extension, the following errors were reported
from Xdmx:


XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1

XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4

XCopyPlane: Tests 13, 22, 31 (well-known XTEST/Xinerama interaction issue)
XDrawLine: Test 67
XDrawLines: Test 91
XDrawSegments: Test 68

Note that the first two sets of errors are the same as for the XFree86 4.3.0
server, and that the XCopyPlane error is a well-known error resulting from an
XTEST/Xinerama interaction when the request crosses a screen boundary. The
XDraw* errors are resolved when the tests are run individually and they do not
cross a screen boundary. We will investigate these errors further to determine
their cause.

Xdmx with XTEST, with Xinerama, with GLX

With GLX enabled, using the XTEST extension, the following errors were reported
from Xdmx (these results are from early during the Phase IV development, but
were confirmed with a late Phase IV snapshot):


XListPixmapFormats: Test 1
XChangeKeyboardControl: Tests 9, 10
XRebindKeysym: Test 1

XAllowEvents: Tests 20, 21, 24
XGrabButton: Tests 5, 9-12, 14, 16, 19, 21-25
XGrabKey: Test 8
XSetPointerMapping: Test 3
XUngrabButton: Test 4

XClearArea: Test 8
XCopyArea: Tests 4, 5, 11, 14, 17, 23, 25, 27, 30
XCopyPlane: Tests 6, 7, 10, 19, 22, 31
XDrawArcs: Tests 89, 100, 102
XDrawLine: Test 67
XDrawSegments: Test 68

Note that the first two sets of errors are the same as for the XFree86 4.3.0
server, and that the third set has different failures than when Xdmx does not
include GLX support. Since the GLX extension adds new visuals to support GLX's
visual configs and the X Test Suite runs tests over the entire set of visuals,
additional rendering tests were run and presumably more of them crossed a
screen boundary. This conclusion is supported by the fact that nearly all of
the rendering errors reported are resolved when the tests are run individually
and they do no cross a screen boundary.

Further, when hardware rendering is disabled on the back-end displays, many of
the errors in the third set are eliminated, leaving only:


XClearArea: Test 8
XCopyArea: Test 4, 5, 11, 14, 17, 23, 25, 27, 30
XCopyPlane: Test 6, 7, 10, 19, 22, 31

Conclusion

We conclude that all of the X Test Suite errors reported for Xdmx are the
result of errors in the back-end X server or the Xinerama implementation.
Further, all of these errors that can be reasonably fixed at the Xdmx layer
have been. (Where appropriate, we have submitted patches to the XFree86 and
Xinerama upstream maintainers.)

Dynamic Reconfiguration

During this development phase, dynamic reconfiguration support was added to
DMX. This support allows an application to change the position and offset of a
back-end server's screen. For example, if the application would like to shift a
screen slightly to the left, it could query Xdmx for the screen's <x,y>
position and then dynamically reconfigure that screen to be at position
<x+10,y>. When a screen is dynamically reconfigured, input handling and a
screen's root window dimensions are adjusted as needed. These adjustments are
transparent to the user.

Dynamic reconfiguration extension

The application interface to DMX's dynamic reconfiguration is through a
function in the DMX extension library:

Bool DMXReconfigureScreen(Display *dpy, int screen, int x, int y)

where dpy is DMX server's display, screen is the number of the screen to be
reconfigured, and x and y are the new upper, left-hand coordinates of the
screen to be reconfigured.

The coordinates are not limited other than as required by the X protocol, which
limits all coordinates to a signed 16 bit number. In addition, all coordinates
within a screen must also be legal values. Therefore, setting a screen's upper,
left-hand coordinates such that the right or bottom edges of the screen is
greater than 32,767 is illegal.

Bounding box

When the Xdmx server is started, a bounding box is calculated from the screens'
layout given either on the command line or in the configuration file. This
bounding box is currently fixed for the lifetime of the Xdmx server.

While it is possible to move a screen outside of the bounding box, it is
currently not possible to change the dimensions of the bounding box. For
example, it is possible to specify coordinates of <-100,-100> for the upper,
left-hand corner of the bounding box, which was previously at coordinates
<0,0>. As expected, the screen is moved down and to the right; however, since
the bounding box is fixed, the left side and upper portions of the screen
exposed by the reconfiguration are no longer accessible on that screen. Those
inaccessible regions are filled with black.

This fixed bounding box limitation will be addressed in a future development
phase.

Sample applications

An example of where this extension is useful is in setting up a video wall. It
is not always possible to get everything perfectly aligned, and sometimes the
positions are changed (e.g., someone might bump into a projector). Instead of
physically moving projectors or monitors, it is now possible to adjust the
positions of the back-end server's screens using the dynamic reconfiguration
support in DMX.

Other applications, such as automatic setup and calibration tools, can make use
of dynamic reconfiguration to correct for projector alignment problems, as long
as the projectors are still arranged rectilinearly. Horizontal and vertical
keystone correction could be applied to projectors to correct for
non-rectilinear alignment problems; however, this must be done external to
Xdmx.

A sample test program is included in the DMX server's examples directory to
demonstrate the interface and how an application might use dynamic
reconfiguration. See dmxreconfig.c for details.

Additional notes

In the original development plan, Phase IV was primarily devoted to adding
OpenGL support to DMX; however, SGI became interested in the DMX project and
developed code to support OpenGL/GLX. This code was later donated to the DMX
project and integrated into the DMX code base, which freed the DMX developers
to concentrate on dynamic reconfiguration (as described above).

Doxygen documentation

Doxygen is an open-source (GPL) documentation system for generating browseable
documentation from stylized comments in the source code. We have placed all of
the Xdmx server and DMX protocol source code files under Doxygen so that
comprehensive documentation for the Xdmx source code is available in an easily
browseable format.

Valgrind

Valgrind, an open-source (GPL) memory debugger for Linux, was used to search
for memory management errors. Several memory leaks were detected and repaired.
The following errors were not addressed:

 1. When the X11 transport layer sends a reply to the client, only those fields
    that are required by the protocol are filled in -- unused fields are left
    as uninitialized memory and are therefore noted by valgrind. These
    instances are not errors and were not repaired.

 2. At each server generation, glxInitVisuals allocates memory that is never
    freed. The amount of memory lost each generation approximately equal to 128
    bytes for each back-end visual. Because the code involved is automatically
    generated, this bug has not been fixed and will be referred to SGI.

 3. At each server generation, dmxRealizeFont calls XLoadQueryFont, which
    allocates a font structure that is not freed. dmxUnrealizeFont can free the
    font structure for the first screen, but cannot free it for the other
    screens since they are already closed by the time dmxUnrealizeFont could
    free them. The amount of memory lost each generation is approximately equal
    to 80 bytes per font per back-end. When this bug is fixed in the the X
    server's device-independent (dix) code, DMX will be able to properly free
    the memory allocated by XLoadQueryFont.

RATS

RATS (Rough Auditing Tool for Security) is an open-source (GPL) security
analysis tool that scans source code for common security-related programming
errors (e.g., buffer overflows and TOCTOU races). RATS was used to audit all of
the code in the hw/dmx directory and all "High" notations were checked
manually. The code was either re-written to eliminate the warning, or a comment
containing "RATS" was inserted on the line to indicate that a human had checked
the code. Unrepaired warnings are as follows:

 1. Fixed-size buffers are used in many areas, but code has been added to
    protect against buffer overflows (e.g., XmuSnprint). The only instances
    that have not yet been fixed are in config/xdmxconfig.c (which is not part
    of the Xdmx server) and input/usb-common.c.

 2. vprintf and vfprintf are used in the logging routines. In general, all uses
    of these functions (e.g., dmxLog) provide a constant format string from a
    trusted source, so the use is relatively benign.

 3. glxProxy/glxscreens.c uses getenv and strcat. The use of these functions is
    safe and will remain safe as long as ExtensionsString is longer then
    GLXServerExtensions (ensuring this may not be ovious to the casual
    programmer, but this is in automatically generated code, so we hope that
    the generator enforces this constraint).

