[Cin] OpenCL on CPU

[Andrew Randrianasulu]

note, openCL is different to openGL, mostly being more about more accurate
computations.

On AMD FX4300, 32bit userspace but llvm probably uses avx?


guest at slax:/dev/shm/mesa/BUILD$ RUSTICL_ENABLE=llvmpipe  clpeak

Platform: rusticl
  Device: llvmpipe (LLVM 20.1.3, 256 bits)
    Driver version  : 25.2.0-devel (git-845611bb43) (Linux x86)
    Compute units   : 8
    Clock frequency : 300 MHz

    Global memory bandwidth (GBPS)
      float   : 3.72
      float2  : 4.08
      float4  : 3.59
      float8  : 2.81
      float16 : 2.09

    Single-precision compute (GFLOPS)
      float   : 14.67
      float2  : 17.86
      float4  : 15.99
      float8  : 14.72
      float16 : 14.63

    No half precision support! Skipped

    No double precision support! Skipped

    Integer compute (GIOPS)
      int   : 13.89
      int2  : 13.25
      int4  : 12.85
                              int8  : 13.04
      int16 : 11.51

    Integer compute Fast 24bit (GIOPS)
                             int   : 13.65
      int2  : 13.29
      int4  : 13.23
                              int8  : 12.90
      int16 : 11.08

    Transfer bandwidth (GBPS)
      enqueueWriteBuffer              : 2.82
                             enqueueReadBuffer               : 1.08
      enqueueWriteBuffer non-blocking : 2.89
      enqueueReadBuffer non-blocking  : 1.02
      enqueueMapBuffer(for read)      : 1.15
        memcpy from mapped ptr        : 3.02
      enqueueUnmap(after write)       : 2.22
        memcpy to mapped ptr          : 3.01

    Kernel launch latency : 21.55 us

guest at slax:/dev/shm/mesa/BUILD$

command to build somewhat minimal mesa (llvmpipe + amd):


meson ../ --prefix=/usr/X11R7 --libdir=lib --strip --buildtype
debugoptimized -Degl=enabled -Dosmesa=true -Dplatforms=x11
-Dgallium-drivers=r600,radeonsi,llvmpipe -Dvulkan-drivers=amd,swrast
-Dgallium-nine=true -Dgallium-va=enabled  -Dgallium-xa=disabled
-Dgallium-rusticl=true -Dllvm=enabled -Drust_std=2021  -Dvideo-codecs="all"

of course you can set your own prefix ( I have X installed into non-default
location).

Biggest obstacle for me was that mesa git require some new llvm, and just
released two days ago SPIRV-Tools-2024.4 !

And github "release" is of course broken, in sense you need to manually
fetch headers at specific commit.

Of course "real gpu" will get like >200 GFLOPS , even my puny GF710 was
that fast, but possibility of lock up makes this option less attractive ;)
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