[Intel-gfx] [PATCHv2] drm/i915: Remove WaDisableLSQCROPERFforOCL KBL workaround.

[Daniel Vetter]

On Mon, Jan 09, 2017 at 01:07:56PM -0800, Francisco Jerez wrote:
> The WaDisableLSQCROPERFforOCL workaround has the side effect of
> disabling an L3SQ optimization that has huge performance implications
> and is unlikely to be necessary for the correct functioning of usual
> graphic workloads.  Userspace is free to re-enable the workaround on
> demand, and is generally in a better position to determine whether the
> workaround is necessary than the DRM is (e.g. only during the
> execution of compute kernels that rely on both L3 fences and HDC R/W
> requests).
> 
> The same workaround seems to apply to BDW (at least to production
> stepping G1) and SKL as well (the internal workaround database claims
> that it does for all steppings, while the BSpec workaround table only
> mentions pre-production steppings), but the DRM doesn't do anything
> beyond whitelisting the L3SQCREG4 register so userspace can enable it
> when it sees fit.  Do the same on KBL platforms.
> 
> Improves performance of the GFXBench4 gl_manhattan31 benchmark by 60%,
> and gl_4 (AKA car chase) by 14% on a KBL GT2 running Mesa master --
> This is followed by a regression of 35% and 10% respectively for the
> same benchmarks and platform caused by my recent patch series
> switching userspace to use the dataport constant cache instead of the
> sampler to implement uniform pull constant loads, which caused us to
> hit more heavily the L3 cache (and on platforms other than KBL had the
> opposite effect of improving performance of the same two benchmarks).
> The overall effect on KBL of this change combined with the recent
> userspace change is respectively 4.6% and 2.6%.  SynMark2 OglShMapPcf
> was affected by the constant cache changes (though it improved as it
> did on other platforms rather than regressing), but is not
> significantly affected by this patch (with statistical significance of
> 5% and sample size 20).
> 
> v2: Drop some more code to avoid unused variable warning.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99256
> Signed-off-by: Francisco Jerez <currojerez at riseup.net>
> Cc: Eero Tamminen <eero.t.tamminen at intel.com>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Cc: beignet at lists.freedesktop.org

Don't we need some userspace flag/opt-in scheme to avoid stuff going boom
for compute kernels? Are the patches for mesa compute/beignet
ready&reviewed?
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_lrc.c        | 10 ----------
>  drivers/gpu/drm/i915/intel_ringbuffer.c |  8 --------
>  2 files changed, 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 6db246a..656e0a3 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -970,18 +970,8 @@ static inline int gen8_emit_flush_coherentl3_wa(struct intel_engine_cs *engine,
>  						uint32_t *batch,
>  						uint32_t index)
>  {
> -	struct drm_i915_private *dev_priv = engine->i915;
>  	uint32_t l3sqc4_flush = (0x40400000 | GEN8_LQSC_FLUSH_COHERENT_LINES);
>  
> -	/*
> -	 * WaDisableLSQCROPERFforOCL:kbl
> -	 * This WA is implemented in skl_init_clock_gating() but since
> -	 * this batch updates GEN8_L3SQCREG4 with default value we need to
> -	 * set this bit here to retain the WA during flush.
> -	 */
> -	if (IS_KBL_REVID(dev_priv, 0, KBL_REVID_E0))
> -		l3sqc4_flush |= GEN8_LQSC_RO_PERF_DIS;
> -
>  	wa_ctx_emit(batch, index, (MI_STORE_REGISTER_MEM_GEN8 |
>  				   MI_SRM_LRM_GLOBAL_GTT));
>  	wa_ctx_emit_reg(batch, index, GEN8_L3SQCREG4);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 0971ac3..7cb2ab4 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1095,14 +1095,6 @@ static int kbl_init_workarounds(struct intel_engine_cs *engine)
>  		WA_SET_BIT_MASKED(HDC_CHICKEN0,
>  				  HDC_FENCE_DEST_SLM_DISABLE);
>  
> -	/* GEN8_L3SQCREG4 has a dependency with WA batch so any new changes
> -	 * involving this register should also be added to WA batch as required.
> -	 */
> -	if (IS_KBL_REVID(dev_priv, 0, KBL_REVID_E0))
> -		/* WaDisableLSQCROPERFforOCL:kbl */
> -		I915_WRITE(GEN8_L3SQCREG4, I915_READ(GEN8_L3SQCREG4) |
> -			   GEN8_LQSC_RO_PERF_DIS);
> -
>  	/* WaToEnableHwFixForPushConstHWBug:kbl */
>  	if (IS_KBL_REVID(dev_priv, KBL_REVID_C0, REVID_FOREVER))
>  		WA_SET_BIT_MASKED(COMMON_SLICE_CHICKEN2,
> -- 
> 2.10.2
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch