Re: [PATCH] drm/i915: Enable eLLC caching of display buffers for SKL+

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Apr 16, 2019 at 05:28:57PM +0300, Eero Tamminen wrote:
> Hi,
> 
> Based on quick tests with the patch:
> 
> * Results in GfxBench and Unigine (Valley/Heaven) tests were within 
> daily variation on the tested SKL machines
> 
> * SKL GT4e (128MB eLLC) / Wayland / Weston:
>    +15-20% SynMark TexMem512 (512MB of textures)
>     +4-6% SynMark TerrainFly*, CSCloth, ShMapVsm
>    -5-10% SynMark TexMem128 (128MB of textures)

These seem mostly good. The 128MB case regression seems
understandable since we don't quite fit into the eLLC
anymore.

> 
> * SKL GT3e (64MB eLLC) / Xorg / Unity:
>    +4-8% GpuTest Triangle fullscreen (FullHD)
>   -5-10% GpuTest Triangle windowed (1/2 screen)

Not quite sure why the windowed case would suffer here :/

> 
> * SKL GT2 (no eLLC) / Xorg / Unity:
>    * Some of the higher FPS SynMark pixel and vertex shader tests
>      are few percent higher, more than daily variance
>    => Do you see any reason why this machine would be impacted
>       although it doesn't eLLC?

Can't think of a reason for that. All display buffers should still
be UC on such a machine.

> 
> (I built it against drm-tip and compared results against previous and 
> next day unpatched drm-tip results that I had otherwise.)
> 
> 
> 	- Eero
> 
> On 15.4.2019 17.16, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Since SKL the eLLC has been sitting on the far side of the system
> > agent, meaning the display engine can utilize it. Let's enable that.
> > 
> > I chose WB for the caching mode, because my numbers are indicating
> > that WT might actually be WB and WC might actually be UC. I'm not
> > 100% sure that is indeed the case but at least my simple rendercopy
> > based benchmark didn't see any difference in performance.
> > 
> > Also if I configure things to do LLCeLLC+WT I still get cache dirt
> > on my screen, suggesting that is in fact operating in WB mode
> > anyway. This is also the reason I had to fix the MOCS target cache
> > to really say PTE rather than LLC+eLLC.
> > 
> > Caveat: I've not benchmarked any real workloads. IIRC Eero did
> > benchmark an earlier version, but that didn't have the PTE vs.
> > LLC+eLLC MOCS fix so it wasn't actually doing the right thing
> > most likely.
> > 
> > Cc: Eero Tamminen <eero.t.tamminen@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_drv.h     | 3 +--
> >   drivers/gpu/drm/i915/i915_gem_gtt.c | 7 +++++--
> >   drivers/gpu/drm/i915/i915_gem_gtt.h | 2 +-
> >   drivers/gpu/drm/i915/intel_mocs.c   | 2 +-
> >   4 files changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 35d0782c077e..2a4f33fa2bba 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -2517,8 +2517,7 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
> >   #define HAS_LLC(dev_priv)	(INTEL_INFO(dev_priv)->has_llc)
> >   #define HAS_SNOOP(dev_priv)	(INTEL_INFO(dev_priv)->has_snoop)
> >   #define HAS_EDRAM(dev_priv)	((dev_priv)->edram_size_mb)
> > -#define HAS_WT(dev_priv)	((IS_HASWELL(dev_priv) || \
> > -				 IS_BROADWELL(dev_priv)) && HAS_EDRAM(dev_priv))
> > +#define HAS_WT(dev_priv)	HAS_EDRAM(dev_priv)
> >   
> >   #define HWS_NEEDS_PHYSICAL(dev_priv)	(INTEL_INFO(dev_priv)->hws_needs_physical)
> >   
> > diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > index 8f460cc4cc1f..038fbf52a997 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > @@ -3071,7 +3071,7 @@ static void cnl_setup_private_ppat(struct intel_ppat *ppat)
> >   
> >   	__alloc_ppat_entry(ppat, 0, GEN8_PPAT_WB | GEN8_PPAT_LLC);
> >   	__alloc_ppat_entry(ppat, 1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC);
> > -	__alloc_ppat_entry(ppat, 2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC);
> > +	__alloc_ppat_entry(ppat, 2, GEN8_PPAT_WB | GEN8_PPAT_ELLC_OVERRIDE);
> >   	__alloc_ppat_entry(ppat, 3, GEN8_PPAT_UC);
> >   	__alloc_ppat_entry(ppat, 4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0));
> >   	__alloc_ppat_entry(ppat, 5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1));
> > @@ -3109,7 +3109,10 @@ static void bdw_setup_private_ppat(struct intel_ppat *ppat)
> >   
> >   	__alloc_ppat_entry(ppat, 0, GEN8_PPAT_WB | GEN8_PPAT_LLC);      /* for normal objects, no eLLC */
> >   	__alloc_ppat_entry(ppat, 1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC);  /* for something pointing to ptes? */
> > -	__alloc_ppat_entry(ppat, 2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC);  /* for scanout with eLLC */
> > +	if (INTEL_GEN(ppat->i915) >= 9)
> > +		__alloc_ppat_entry(ppat, 2, GEN8_PPAT_WB | GEN8_PPAT_ELLC_OVERRIDE); /* for scanout with eLLC */
> > +	else
> > +		__alloc_ppat_entry(ppat, 2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC); /* for scanout with eLLC */
> >   	__alloc_ppat_entry(ppat, 3, GEN8_PPAT_UC);                      /* Uncached objects, mostly for scanout */
> >   	__alloc_ppat_entry(ppat, 4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0));
> >   	__alloc_ppat_entry(ppat, 5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1));
> > diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> > index f597f35b109b..47adc7268867 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> > @@ -139,7 +139,7 @@ typedef u64 gen8_ppgtt_pml4e_t;
> >   #define PPAT_UNCACHED			(_PAGE_PWT | _PAGE_PCD)
> >   #define PPAT_CACHED_PDE			0 /* WB LLC */
> >   #define PPAT_CACHED			_PAGE_PAT /* WB LLCeLLC */
> > -#define PPAT_DISPLAY_ELLC		_PAGE_PCD /* WT eLLC */
> > +#define PPAT_DISPLAY_ELLC		_PAGE_PCD /* WT LLCeLLC (HSW/BDW) or WB eLLC (SKL+) */
> >   
> >   #define CHV_PPAT_SNOOP			(1<<6)
> >   #define GEN8_PPAT_AGE(x)		((x)<<4)
> > diff --git a/drivers/gpu/drm/i915/intel_mocs.c b/drivers/gpu/drm/i915/intel_mocs.c
> > index 274ba78500c0..d984ccff94ef 100644
> > --- a/drivers/gpu/drm/i915/intel_mocs.c
> > +++ b/drivers/gpu/drm/i915/intel_mocs.c
> > @@ -115,7 +115,7 @@ struct drm_i915_mocs_table {
> >   		   LE_1_UC | LE_TC_2_LLC_ELLC, \
> >   		   L3_1_UC), \
> >   	MOCS_ENTRY(I915_MOCS_PTE, \
> > -		   LE_0_PAGETABLE | LE_TC_2_LLC_ELLC | LE_LRUM(3), \
> > +		   LE_0_PAGETABLE | LE_TC_0_PAGETABLE | LE_LRUM(3), \
> >   		   L3_3_WB)
> >   
> >   static const struct drm_i915_mocs_entry skylake_mocs_table[] = {
> > 

-- 
Ville Syrjälä
Intel
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