extensions/img/cl_img_cached_allocations.txt

Name

    IMG_cached_allocations

Name Strings

    cl_img_cached_allocations

Contributors

    Jeremy Kemp

Contacts

    Jeremy Kemp, Imagination Technologies (jeremy.kemp 'at' imgtec.com)

Status

    Unapproved.

Version

    Revision: #3, Nov 6, 2014

Number

    OpenCL Extension #44

Dependencies

    Requires OpenCL version 1.2 or later.

    This extension is written against the wording of the OpenCL 1.2
    Specification.

Overview

    This extension extends the functionality provided by
    clCreateBuffer and clCreateImage to allow the OpenCL
    implementation to allocate memory on the device which
    is also cached on the host CPU.

Glossary

    None

New Types

    None

New Procedures and Functions

    None

New Tokens

    CL_MEM_USE_UNCACHED_CPU_MEMORY_IMG           (1 << 26)

    CL_MEM_USE_CACHED_CPU_MEMORY_IMG           (1 << 27)

Additions to Chapter 5 of the OpenCL 1.2 Specification (Memory Objects)

    In Table 5.3, page 69, add the following text as a new row in the table:

    "CL_MEM_USE_UNCACHED_CPU_MEMORY_IMG

      If this flag is specified it means that the application wants the
      OpenCL implementation to allocate memory on the device so that it
      is not cached when accessed on the host."

    In Table 5.3, page 69, add the following text as a new row in the table:

    "CL_MEM_USE_CACHED_CPU_MEMORY_IMG

      If this flag is specified it means that the application wants the
      OpenCL implementation to allocate memory on the device so that it
      is cached when accessed on the host."

Issues

    1.  This extension may or may not improve performance; it depends on the
        specific use-case. It is most likely to improve performance in cases
        where the buffer or image is mapped using clEnqueueMapBuffer/Image
        and some processing is then performed on the host-side. Whether the
        allocation flag improves performance depends on whether the overhead
        of cache flushes is greater than the performance gain  from cached
        memory accessing when doing the host-side processing. It's recommended
        to apply the flag on case-by-case basis to see if it improves your
        use-case.

Revision History

#2    - Update overview section to say that the extension also supports images.
        Add more detail to the overview section.

#1    - Initial revision.