[Mesa-dev] [PATCH 8/8] i965: Use the correct number of threads for compute shaders.

[Kenneth Graunke]

We were programming the number of threads per subslice, when we should
have been programming the total number of threads on the GPU as a whole.

Thanks to Curro and Jordan for helping track this down!

On Skylake GT3e:
- Improves performance in Unreal's Elemental Demo by roughly 1.5-1.7x.
- Improves performance in Synmark's Gl43CSDof by roughly 3.7x.
- Improves performance in Synmark's Gl43GSCloth by roughly 1.18x.

On Broadwell GT2:
- Improves performance in Unreal's Elemental Demo by roughly 1.2-1.5x.
- Improves performance in Synmark's Gl43CSDof by roughly 2.0x.
- Improves performance in Synmark's Gl43GSCloth by 1.47035% +/-
  0.255654% (n=25).

On Haswell GT3e:
- Improves performance in Unreal's Elemental Demo (in GL 4.3 mode)
  by roughly 1.10x.
- Improves performance in Synmark's Gl43CSDof by roughly 1.18x.
- Decreases performance in Synmark's Gl43CSCloth by -1.99484% +/-
  0.432771% (n=64).

On Ivybridge GT2:
- Improves performance in Unreal's Elemental Demo (in GL 4.2 mode)
  by roughly 1.03x.
- Improves performance in Synmark's G/43CSDof by roughly 1.25x.
- No change in Synmark's Gl43CSCloth (n=28).

Cc: "12.0" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/gen7_cs_state.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/gen7_cs_state.c b/src/mesa/drivers/dri/i965/gen7_cs_state.c
index 9d83837..ba558a6 100644
--- a/src/mesa/drivers/dri/i965/gen7_cs_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_cs_state.c
@@ -95,7 +95,9 @@ brw_upload_cs_state(struct brw_context *brw)
    const uint32_t vfe_num_urb_entries = brw->gen >= 8 ? 2 : 0;
    const uint32_t vfe_gpgpu_mode =
       brw->gen == 7 ? SET_FIELD(1, GEN7_MEDIA_VFE_STATE_GPGPU_MODE) : 0;
-   OUT_BATCH(SET_FIELD(brw->max_cs_threads - 1, MEDIA_VFE_STATE_MAX_THREADS) |
+   const uint32_t subslices = MAX2(brw->intelScreen->subslice_total, 1);
+   OUT_BATCH(SET_FIELD(brw->max_cs_threads * subslices - 1,
+                       MEDIA_VFE_STATE_MAX_THREADS) |
              SET_FIELD(vfe_num_urb_entries, MEDIA_VFE_STATE_URB_ENTRIES) |
              SET_FIELD(1, MEDIA_VFE_STATE_RESET_GTW_TIMER) |
              SET_FIELD(1, MEDIA_VFE_STATE_BYPASS_GTW) |
-- 
2.8.3