[PATCH] drm/i915: Make sample_c messages go faster on Haswell.

Kenneth Graunke
2015-01-01T00:32:17Z

Haswell significantly improved the performance of sampler_c messages,
but the optimization appears to be off by default. Later platforms
remove this bit, and apparently always enable the optimization.

Improves performance in "Counter Strike: Global Offensive" by 18%
at default settings on Iris Pro.

This may break sampling of paletted formats (P8/A8P8/P8A8). It's
unclear whether it affects sampling of paletted formats in general,
or just the sample_c message (which is never used).

While libva does have support for using paletted formats (primarily
for OSDs), that support appears to have been broken for at least a
year, so I couldn't observe a regression from this.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
---
drivers/gpu/drm/i915/i915_reg.h | 1 +
drivers/gpu/drm/i915/intel_pm.c | 4 ++++
2 files changed, 5 insertions(+)

Resubmitting the patch to unconditionally enable this. I tried to get
libva-intel to use paletted formats, and observe a regression...but the
only thing I found that used it was mplayer's OSD (on screen display).
Even without my patch, the colors were totally wrong with that, and it's
according to a few distro wikis, that's been the case for over a year.

If libva's code for paletted formats /is/ broken, they could always add
code to disable this bit using the command validator when fixing it.

Could we try merging this, and back it out if someone reports a
regression? I haven't observed any problems. It's also been quite
stable.

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 40ca873..0f32fd1a 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -6167,6 +6167,7 @@ enum punit_power_well {
#define HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_DISABLE (1 << 6)

#define HALF_SLICE_CHICKEN3 0xe184
+#define HSW_SAMPLE_C_PERFORMANCE (1<<9)
#define GEN8_CENTROID_PIXEL_OPT_DIS (1<<8)
#define GEN8_SAMPLER_POWER_BYPASS_DIS (1<<1)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 7d99a9c..17e84dc 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5974,6 +5974,10 @@ static void haswell_init_clock_gating(struct drm_device *dev)
I915_WRITE(GEN7_GT_MODE,
_MASKED_FIELD(GEN6_WIZ_HASHING_MASK, GEN6_WIZ_HASHING_16x4));

+ /* Make sample_c messages faster. */
+ I915_WRITE(HALF_SLICE_CHICKEN3,
+ _MASKED_BIT_ENABLE(HSW_SAMPLE_C_PERFORMANCE));
+
/* WaSwitchSolVfFArbitrationPriority:hsw */
I915_WRITE(GAM_ECOCHK, I915_READ(GAM_ECOCHK) | HSW_ECOCHK_ARB_PRIO_SOL);

--
2.2.1