[Mesa-dev] [PATCH] i965: Pretend there are 4 subslices for compute shader threads on Gen9+.

[Kenneth Graunke]

Similar to what we did for pixel shader threads - see gen_device_info.c.

We don't want to bump the actual Maximum Number of Threads though, so
we adjust it here.  For pixel shaders, we don't use max_wm_threads, so
we could just bump it globally.

Fixes Piglit tests:
arb_gpu_shader_int64/execution/built-in-functions/cs-op-div-i64vec3-int64_t
arb_gpu_shader_int64/execution/built-in-functions/cs-op-div-i64vec4-int64_t
arb_gpu_shader_int64/execution/built-in-functions/cs-op-div-u64vec4-uint64_t
---
 src/mesa/drivers/dri/i965/brw_program.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_program.c b/src/mesa/drivers/dri/i965/brw_program.c
index 7607bc38840..5ecfb9f5b11 100644
--- a/src/mesa/drivers/dri/i965/brw_program.c
+++ b/src/mesa/drivers/dri/i965/brw_program.c
@@ -357,7 +357,19 @@ brw_alloc_stage_scratch(struct brw_context *brw,
       thread_count = devinfo->max_wm_threads;
       break;
    case MESA_SHADER_COMPUTE: {
-      const unsigned subslices = MAX2(brw->screen->subslice_total, 1);
+      unsigned subslices = MAX2(brw->screen->subslice_total, 1);
+
+      /* The documentation for 3DSTATE_PS "Scratch Space Base Pointer" says:
+       *
+       * "Scratch Space per slice is computed based on 4 sub-slices.  SW must
+       *  allocate scratch space enough so that each slice has 4 slices
+       *  allowed."
+       *
+       * According to the other driver team, this applies to compute shaders
+       * as well.  This is not currently documented at all.
+       */
+      if (devinfo->gen >= 9)
+         subslices = 4;
 
       /* WaCSScratchSize:hsw
        *
-- 
2.15.0