[Mesa-dev] [Mesa3d-dev] Softpipe and OpenMP

Chih-Sheng Lin patrickcslin at gmail.com
Mon Jun 8 00:33:20 PDT 2015


I am working on parallelizing softpipe of Mesa-9.1 by using OpenMP.

My idea is trying to do sp_setup_tri in parallel with multiple threads.

So first in the function sp_vbuf_draw_elements, I duplicate setup_context
for avoiding race condition

And then sp_setup_tri is set to OpenMP parallel sections with the separate

The code is as follows:

sp_vbuf_draw_elements(struct vbuf_render *vbr, const ushort *indices, uint
   struct softpipe_vbuf_render *cvbr = softpipe_vbuf_render(vbr);
   struct softpipe_context *softpipe = cvbr->softpipe;
   const unsigned stride = softpipe->vertex_info_vbuf.size * sizeof(float);
   const void *vertex_buffer = cvbr->vertex_buffer;
   struct setup_context *setup = cvbr->setup;

/*duplicate setup context*/
struct setup_context *setup_0, *setup_1;
if(cvbr->prim == PIPE_PRIM_TRIANGLES)
    setup_0 = sp_setup_create_context(cvbr->setup);
    setup_1 = sp_setup_create_context(cvbr->setup);


      for (i = 2; i < nr; i += 3) {
         sp_setup_tri( setup,
                       get_vert(vertex_buffer, indices[i-2], stride),
                       get_vert(vertex_buffer, indices[i-1], stride),
                       get_vert(vertex_buffer, indices[i-0], stride) );

/*parallelizing sp_setup_tri by OpenMP parallel sections*/
    #pragma omp parallel sections
        #pragma omp section
        sp_setup_tri(setup_0, get_vert(vertex_buffer, indices[0], stride),
get_vert(vertex_buffer, indices[1], stride),get_vert(vertex_buffer,
indices[2], stride));
        #pragma omp section
        sp_setup_tri(setup_1, get_vert(vertex_buffer, indices[3], stride),
get_vert(vertex_buffer, indices[4], stride),get_vert(vertex_buffer,
indices[5], stride));


And I rebuild mesa and run one test called CPUOverheadTest_onscreen from
GFXBench 2.7.5

I set OMP_NUM_THREADS=2 and the resolution is 1280x900, it gains 10%
performance improvements comparing to OMP_NUM_THREADS=1

However, the test result is not correct, but it works very well comparing
to my first attempt on parallelization

Could someone give me a guide or suggestions for this work?

Thanks in advance!

Patrick Lin
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