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

[Francisco Jerez]

Daniel Vetter <daniel at ffwll.ch> writes:

> 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?

I don't think upstream userspace (neither Beignet nor Mesa) relies on
the workaround at this point, though Beignet devs may want to keep this
hardware bug in mind when they start doing SVM.

> -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
>> 
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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