Name

    AMD_gpu_association

Name Strings

    GLX_AMD_gpu_association

Contact

    David Mao, AMD (david.mao 'at' amd.com)

Status

    Complete

Version

    Last Modified Date: September 18, 2014
    Author Revision: 2

    Based on:  GLX_SGI_make_current_read specification
               Date: 3/20/1997

               EXT_framebuffer_object specification
               Date: 2/13/2007   Revision #119

Number

    398

Dependencies

    OpenGL 1.5 is required.

    GLX 1.3 is required.

    GL_EXT_framebuffer_object is required.

    GLX_ARB_get_proc_address is required.

    This extension interacts with GLX_SGI_make_current_read.

    This extension interacts with GL_EXT_framebuffer_blit.

    This extension interacts with GLX_ARB_create_context.

    This extension interacts with WGL_AMD_gpu_association.

Overview


    There currently is no way for applications to efficiently use GPU
    resources in systems that contain more than one GPU. Vendors have
    provided methods that attempt to split the workload for an
    application among the available GPU resources. This has proven to be
    very inefficient because most applications were never written with
    these sorts of optimizations in mind.

    This extension provides a mechanism for applications to explicitly
    use the GPU resources on a given system individually. By providing
    this functionality, a driver allows applications to make appropriate
    decisions regarding where and when to distribute rendering tasks.

    The set of GPUs available on a system can be queried by calling
    glXGetGPUIDsAMD. The current GPU assigned to a specific context
    can be determined by calling glXGetContextGPUIDAMD. Each GPU in a
    system may have different performance characteristics in addition
    to supporting a different version of OpenGL. The specifics of each
    GPU can be obtained by calling glXGetGPUInfo. This will allow
    applications to pick the most appropriate GPU for each rendering
    task.

    Once all necessary GPU information has been obtained, a context tied
    to a specific GPU can be created with glXCreateAssociatedContextAMD.
    These associated contexts can be made current with
    glXMakeAssociatedContextCurrentAMD and deleted with
    glXDeleteAssociatedContextAMD. Only one GPU associated or
    non-associated context can be current at one time per thread.

    To provide an accelerated path for blitting data from one context
    to another, the new blit function BlitContextFramebufferAMD has
    been added.


New Procedures and Functions

    unsigned int glXGetGPUIDsAMD(unsigned int maxCount, unsigned int *ids);

    int   glXGetGPUInfoAMD(unsigned int id, int property, GLenum dataType,
                           unsigned int size, void *data)

    unsigned int glXGetContextGPUIDAMD(GLXContext ctx);

    GLXContext glXCreateAssociatedContextAMD(unsigned int id,
                                             GLXContext share_list);

    GLXContext glXCreateAssociatedContextAttribsAMD(unsigned int id,
                                                    GLXContext share_context,
                                                    const int *attribList);

    Bool glXDeleteAssociatedContextAMD(GLXContext ctx);

    Bool glXMakeAssociatedContextCurrentAMD(GLXContext ctx);

    GLXContext glXGetCurrentAssociatedContextAMD(void);

    void glXBlitContextFramebufferAMD(GLXContext dstCtx, GLint srcX0, GLint srcY0,
                                      GLint srcX1, GLint srcY1, GLint dstX0,
                                      GLint dstY0, GLint dstX1, GLint dstY1,
                                      GLbitfield mask, GLenum filter);

New Tokens

    Accepted by the <property> parameter of glXGetGPUInfo:

      GLX_GPU_VENDOR_AMD                 0x1F00
      GLX_GPU_RENDERER_STRING_AMD        0x1F01
      GLX_GPU_OPENGL_VERSION_STRING_AMD  0x1F02
      GLX_GPU_FASTEST_TARGET_GPUS_AMD    0x21A2
      GLX_GPU_RAM_AMD                    0x21A3
      GLX_GPU_CLOCK_AMD                  0x21A4
      GLX_GPU_NUM_PIPES_AMD              0x21A5
      GLX_GPU_NUM_SIMD_AMD               0x21A6
      GLX_GPU_NUM_RB_AMD                 0x21A7
      GLX_GPU_NUM_SPI_AMD                0x21A8

    Accepted by the <dataType> argument of glXGetGPUInfoAMD:

      GL_UNSIGNED_BYTE
      GL_UNSIGNED_INT
      GL_INT
      GL_FLOAT

    Accepted by the <mask> argument of glXBlitContextFramebufferAMD:

      GL_COLOR_BUFFER_BIT
      GL_DEPTH_BUFFER_BIT
      GL_STENCIL_BUFFER_BIT

Additions to the WGL Specification

    None. This specification is written for GLX.

Additions to the GLX 1.4 Specification

    Add a new section in between 3.3.7 and 3.3.8 entitled "GPU
    Associated Contexts"

    GPU Associated Contexts

    When multiple GPUs are present, a context can be created for
    off-screen rendering that is associated with a specific GPU.
    This will allow applications to achieve an app-specific
    distributed GPU utilization.

    The IDs for available GPUs can be queried with the command:

        unsigned int glXGetGPUIDsAMD(unsigned int maxCount, unsigned int *ids);

    where <maxCount> is the max number of IDs that can be returned and
    <ids> is the array of returned IDs. If the function succeeds,
    the return value is the number of total GPUs available. The
    value 0 is returned if no GPUs are available or if the call has
    failed. The array pointer <ids> passed into the function will be
    populated by the smaller of maxCount or the total GPU count
    available. The ID 0 is reserved and will not be retuned as a
    valid GPU ID. If the array <ids> is NULL, the function will
    only return the total number of GPUs. <ids> will be tightly packed
    with no 0 values between valid ids.

    Calling glXGetGPUIDsAMD once with <maxCount> set to zero returns
    the total available GPU count which can be used to allocate an
    appropriately sized id array before calling glXGetGPUIDsAMD
    again to query the full set of supported GPUs.

    Each GPU in a system may have different properties, performance
    characteristics and different supported OpenGL versions. To
    determine which GPU is best suited for a specific task the
    following functions may be used:

        int glXGetGPUInfoAMD(unsigned int id, int property, GLenum dataType,
                             unsigned int size, void *data);

    <id> is a GPU id obtained from calling glXGetGPUIDsAMD. The GPU ID
    must be a valid GPU ID. The function will fail if <id> is an invalid
    GPU ID and -1 will be returned. <property> is the information being
    queried. <dataType> may be GL_UNSIGNED_INT, GL_INT, GL_FLOAT, or
    GL_UNSIGNED_BYTE and signals what data type is to be returned. <size>
    signals the size of the data buffer passed into glXGetGPUInfoAMD.
    This is the count of the array of type <dataType>. <data> is the
    buffer which will be filled with the requested information. For a
    string, <size> will be the number of characters allocated and will
    include NULL termination. For arrays of type GL_UNSIGNED_INT, GL_INT,
    and GL_FLOAT <size> will be the array depth. If the function
    succeeds, the number of values written will be returned. If the number
    of values written is equal to <size>, the query should be repeated with
    a larger <data> buffer. Strings should be queried using the
    GL_UNSIGNED_BYTE type, are UTF-8 encoded and will be NULL terminated.
    If the function fails, -1 will be returned.

    <property> defines the GPU property to be queried, and may be one of
    GLX_GPU_OPENGL_VERSION_STRING_AMD, GLX_GPU_RENDERER_STRING_AMD,
    GLX_GPU_FASTEST_TARGET_GPUS_AMD, GLX_GPU_RAM_AMD, GLX_GPU_CLOCK_AMD,
    GLX_GPU_NUM_PIPES_AMD, GLX_GPU_NUM_SIMD_AMD, GLX_GPU_NUM_RB_AMD, or
    GLX_GPU_NUM_SPI_AMD.

    If <size> is not sufficient to hold the entire value for a particular
    property, the number of values returned will equal <size>. If
    <dataType> is inappropriate for <property>, for instance INT for a
    property which is a string, the function will fail and -1 will be
    returned.

    Querying GLX_GPU_OPENGL_VERSION_STRING_AMD returns the highest supported
    OpenGL version string and GLX_GPU_RENDERER_STRING_AMD returns name
    of the GPU. <dataType> must be GL_UNSIGNED_BYTE with the previous
    properties. Querying GLX_GPU_FASTEST_TARGET_GPUS_AMD returns an array
    of the IDs of GPUs with the fastest data blit rates when using
    glXBlitContextFramebufferAMD. This list is ordered fastest
    first. This provides a performance hint about which contexts and GPUS
    are capable of transfering data between each other the quickest. Querying
    GLX_GPU_RAM_AMD returns the amount of RAM available to GPU in MB. Querying
    GLX_GPU_CLOCK_AMD returns the GPU clock speed in MHz.  Querying
    GLX_GPU_NUM_PIPES_AMD returns the nubmer of 3D pipes. Querying
    GLX_GPU_NUM_SIMD_AMD returns the number of SIMD ALU units in each
    shader pipe. Querying GLX_GPU_NUM_RB_AMD returns the number of render
    backends. Querying GLX_GPU_NUM_SPI_AMD returns the number of shader
    parameter interpolaters. If the <parameter> being queried is not
    applicable for the GPU specified by <id>, the value 0 will be returned.

    Unassociated contexts are created by calling glXCreateNewContext.
    Although these contexts are unassociated, their use will still be
    tied to a single GPU in most cases. For this reason it is advantageous
    to be able to query the GPU an existing unassociated context resides
    on. If multiple GPUs are available, it would be undesirable
    to use one for rendering to visible surfaces and then chose the
    same one for off-screen rendering. Use the following command to
    determine which GPU a context is attached to:

        unsigned int glXGetContextGPUIDAMD(GLXContext ctx);

    <ctx> is the context for which the GPU id will be returned. If the
    context is invalid or if an error has occurred, glXGetContextGPUIDAMD
    will return 0.

    To create an associated context, use:

        GLXContext glXCreateAssociatedContextAMD(unsigned int id,
                                                 GLXContext share_list);

    <id> must be a valid GPU id and cannot be 0. <share_list> must either
    be NULL or that of an associated context created with the the same GPU
    ID as <id>. If <share_list> was created using a different ID,
    glXCreateAssociatedContextAMD will fail and return NULL. If a context was
    successfully created the handle will be returned by
    glXCreateAssociatedContextAMD. If a context could not be created, NULL
    will be returned. If a context could not be created, error information
    can be obtained by calling GetLastError. Upon successful creation,
    no pixel format is tied to an associated context and the context is not
    tied to a specific Display. Associated contexts are always direct contexts.
    Associated Contexts always support only GLX_RGBA_TYPE rendering type.

    glXCreateAssociatedContextAMD can generate the following errors:
    GLXBadContext if <share_list> is neither zero nor a valid GLX rendering
    context; BadMatch if the server context state for share list exists in
    an address space that cannot be shared with the newly created context
    or if share list was created on a different screen than the one
    referenced by config; BadAlloc if the server does not have enough resources
    to allocate the new context.

    To create an associated context and request a specific GL version, use:

        GLXContext glXCreateAssociatedContextAttribsAMD(unsigned int id,
                    GLXContext share_list, const int *attribList)

    All capabilities and limitations of glXCreateContextAttribsARB apply
    to glXCreateAssociatedContextAttribsAMD. Additionally, <id> must be
    a valid GPU ID and cannot be 0. If a context was successfully created
    the handle will be returned by glXCreateAssociatedContextAttribsAMD.
    If a context could not be created, NULL will be returned. Upon
    successful creation, no pixel format is tied to an associated context.

    <share_list> must either be NULL or that of an associated context created
    with the the same GPU ID as <id>. If <share_list> was created using a
    different ID, glXCreateAssociatedContextAttribsAMD will fail and return NULL.

    glXCreateAssociatedContextAttribsAMD can generate the following errors:
    GLXBadContext if <share_list> is neither zero nor a valid GLX rendering
    context; BadMatch if the server context state for share list exists in
    an address space that cannot be shared with the newly created context
    or if share list was created on a different screen than the one
    referenced by config; BadAlloc if the server does not have enough resources
    to allocate the new context.

    A context must be deleted once it is no longer needed. Use the
    following call to delete an associated context:

        Bool glXDeleteAssociatedContextAMD(GLXContext ctx);

    If the function succeeds, TRUE will be returned, otherwise FALSE is
    returned. <ctx> must be a valid associated context created by
    calling glXCreateAssociatedContextAMD. If an unassociated context,
    created by calling glXCreateNewContext, is passed into <ctx>, the
    function will fail. An associated context cannot be deleted by calling
    glXDestroyContext. If an associated context is passed into
    glXDestroyContext, the result is undefiend.

    To render using an associated context, it must be made the current
    context for a thread:

        Bool glXMakeAssociatedContextCurrentAMD(GLXContext ctx);

    <ctx> is a context handle created by calling
    glXCreateAssociatedContextAMD. If <ctx> was created using
    glXCreateNewContext, the call will fail, FALSE will be returned and
    the error BadAccess will be generated. If <ctx> is not a valid context
    and not NULL, the call will fail, FALSE will be returned and the error
    GLXBadContext will be generated. If the call succeeds, TRUE will be
    returned. To detach the current associated context, pass NULL as <ctx>.

    Only one type of context can be current to a thread at a time. If an
    unassociated context is current to a thread when
    glXMakeAssociatedContextCurrentAMD is called with a valid <ctx>, it
    is as if glxMakeContextCurrent is called first with a ctx value of NULL.
    If an associated context is current and glxMakeContextCurrent is called
    with a valid context, it is as if glXMakeAssociatedContextCurrentAMD is
    called with a ctx value of NULL.

    The current associated context can be queried by calling:

        GLXContext glXGetCurrentAssociatedContextAMD(void);

    The current associated context is returned on a successful call to
    this function. If no associated context is current, NULL is returned.
    If an unassociated context is current, NULL will be returned.

    An associated context can not be passed in as a parameter into
    glXCopyContext. If an associated context is passed into glXCopyContext,
    the error GLXBadContext will be generated.

    The addresses returned from glXGetProcAddressARB are only valid for the
    current context. It may be invalid to use proc addresses obtained from
    a traditional context with an associated context. Furthermore, the
    OpenGL version and extensions supported on an associated context may
    differ. Each context should be treated seperately, proc addressses
    should be queried for each after context creation.

    Calls to glXSwapBuffers when an associated context is current will have
    no effect.

    There is no way to use pBuffers with associated contexts.

    Overlays and underlays are not supported with associated contexts.

    The same associated context is used for both write and read operations.

    To facilitate high performance data communication between multiple
    contexts, a new function is necessary to blit data from one context
    to another.

    VOID  glXBlitContextFramebufferAMD(GLXContext dstCtx, GLint srcX0, GLint srcY0,
                                       GLint srcX1, GLint srcY1, GLint dstX0,
                                       GLint dstY0, GLint dstX1, GLint dstY1,
                                       GLbitfield mask, GLenum filter);

    <dstCtx> is the context handle for the write context. <mask> is the
    bitwise OR of a number of values indicating which buffers are to be
    copied. The values are GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT, and
    GL_STENCIL_BUFFER_BIT, which are described in section 4.2.3.  The
    pixels corresponding to these buffers are copied from the source
    rectangle, bound by the locations (srcX0, srcY0) and (srcX1, srcY1),
    to the destination rectangle, bound by the locations (dstX0, dstY0)
    and (dstX1, dstY1).  The lower bounds of the rectangle are inclusive,
    while the upper bounds are exclusive.

    The source context is the current GL context. Specifying the current
    GL context as the <dstCtx> will result in the error
    GL_INVALID_OPERATION being generated. If <dstCtx> is invalid, the
    error GL_INVALID_OPERATION will be generated. If no context is
    current at the time of this call, the error GL_INVALID_OPERATION
    will be generated. These errors may be queried by calling glGetError.
    The target framebuffer will be the framebuffer bound to
    GL_DRAW_FRAMEBUFFER_EXT  in the context <dstCtx>. The source framebuffer
    will be the framebuffer bound to GL_READ_FRAMEBUFFER_EXT in the
    currently bound  context.

    The restrictions that apply to the source and destination rectangles
    specified with <srcX0>, <srcY0>, <srcX1>, <srcY1>, <dstX0>, <dstY0>
    <dstX0>, and <dstY0> are the same as those that apply for
    glBlitFramebufferEXT. The same error conditions exist as for
    glBlitFramebufferEXT.

    When called, this function will execute immediately in the currently
    bound context. It is up to the caller to maintain appropriate
    synchronization between the current context and <dstCtx> to ensure
    rendering to the appropriate surfaces has completed on the current
    and <dstCtx> contexts.

Additions to Chapter 4 of the OpenGL 1.5 Specification (Per-Fragment
Operations and the Frame Buffer)
Modify the beginning of section 4.4.1 as follows:

    When an assoicated context is bound, the default state for an associated
    context is invalid for rendering. Because there is no attached window,
    there is no default framebuffer surface to render to. An app created
    framebuffer object must be bound for rendering to be valid. If the
    object bound to GL_FRAMEBUFFER_BINDING_EXT is 0, it is as if the
    framebuffer is incomplete, and an
    GL_INVALID_FRAMEBUFFER_OPERATION_EXT error will be generated
    where rendering is attempted.


New State

    None


Interactions with GL_EXT_framebuffer_blit

    If the framebuffer blit extension is not supported, all language
    referring to glBlitFramebufferEXT and glXBlitContextFramebufferAMD
    is removed.

Interactions with GL_EXT_framebuffer_object

    If GLX_AMD_gpu_association is supported, a context created with it
    will also support EXT_framebuffer_object.


Interactions with GLX_SGI_make_current_read

    If the make current read extension is supported, it is invalid to pass
    an associated context handle as a parameter to
    glXMaketCurrentReadSGI. If an associated context is passed into
    glXMaketCurrentReadSGI, the error GLXBadContext will be generated.

Interactions with GLX_create_context

    If GLX_create_context is not supported, all language
    referring to glXCreateAssociatedContextAttribsAMD is removed.


Issues

    1) Should the language for the new context creation methods be added to
       GLX 1.4 section 3.3.7 or in a new section?

       Resolved. Although it is also possible to add this exension text to
       section 3.3.7, the resulting text would not flow well or be as coherent.


Revision History


    Rev.    Date      Author    Changes
    ----  --------    --------  ---------------------------------------------

      2   09/18/2014  gsellers  Fixed types in function prototypes.
                                Update contact. Minor formatting fixes.
      0.1 11/04/2009  nickh     Initial version.