[Intel-gfx] [PATCH] drm/i915: swizzling support for snb/ivb

[Eric Anholt]

On Mon, 6 Feb 2012 16:45:00 +0100, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Sat, Feb 04, 2012 at 09:59:57PM +0100, Eric Anholt wrote:
> > On Thu,  2 Feb 2012 09:58:12 +0100, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > > We have to do this manually. Somebody had a Great Idea.
> > > 
> > > I've measured speed-ups just a few percent above the noise level
> > > (below 5% for the best case), but no slowdows. Chris Wilson measured
> > > quite a bit more (10-20% above the usual snb variance) on a more
> > > recent and better tuned version of sna, but also recorded a few
> > > slow-downs on benchmarks know for uglier amounts of snb-induced
> > > variance.
> > 
> > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > > index 51a2b0c..86fffd2 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > > @@ -3681,12 +3681,31 @@ i915_gem_idle(struct drm_device *dev)
> > >  	return 0;
> > >  }
> > >  
> > > +void i915_gem_init_swizzling(struct drm_device *dev)
> > > +{
> > > +	drm_i915_private_t *dev_priv = dev->dev_private;
> > > +
> > > +	if (INTEL_INFO(dev)->gen < 6 ||
> > > +	    dev_priv->mm.bit_6_swizzle_x == I915_BIT_6_SWIZZLE_NONE)
> > > +		return;
> > > +
> > > +	I915_WRITE(DISP_ARB_CTL, I915_READ(DISP_ARB_CTL) |
> > > +				 DISP_TILE_SURFACE_SWIZZLING);
> > > +
> > > +	I915_WRITE(TILECTL, I915_READ(TILECTL) | TILECTL_SWZCTL);
> > > +	if (IS_GEN6(dev))
> > > +		I915_WRITE(ARB_MODE, ARB_MODE_ENABLE(ARB_MODE_SWIZZLE_SNB));
> > > +	else
> > > +		I915_WRITE(ARB_MODE, ARB_MODE_ENABLE(ARB_MODE_SWIZZLE_IVB));
> > > +}
> > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
> > > index 861223b..1a93066 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem_tiling.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
> > > @@ -93,8 +93,23 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
> > >  	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
> > >  
> > >  	if (INTEL_INFO(dev)->gen >= 6) {
> > > -		swizzle_x = I915_BIT_6_SWIZZLE_NONE;
> > > -		swizzle_y = I915_BIT_6_SWIZZLE_NONE;
> > > +		uint32_t dimm_c0, dimm_c1;
> > > +		dimm_c0 = I915_READ(MAD_DIMM_C0);
> > > +		dimm_c1 = I915_READ(MAD_DIMM_C1);
> > > +		dimm_c0 &= MAD_DIMM_A_SIZE_MASK | MAD_DIMM_B_SIZE_MASK;
> > > +		dimm_c1 &= MAD_DIMM_A_SIZE_MASK | MAD_DIMM_B_SIZE_MASK;
> > > +		/* Enable swizzling when the channels are populated with
> > > +		 * identically sized dimms. We don't need to check the 3rd
> > > +		 * channel because no cpu with gpu attached ships in that
> > > +		 * configuration. Also, swizzling only makes sense for 2
> > > +		 * channels anyway. */
> > > +		if (dimm_c0 == dimm_c1) {
> > > +			swizzle_x = I915_BIT_6_SWIZZLE_9_10;
> > > +			swizzle_y = I915_BIT_6_SWIZZLE_9;
> > > +		} else {
> > > +			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
> > > +			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
> > > +		}
> > 
> > It looks to me like you're making the HW always swizzle bit 6 according
> > to 9 or 9/10 in i915_gem_init_swizzling, but you're not performing the
> > software side of swizzling in the !dual channel case.  My guess would be
> > that when you take your other DIMM the swizzling for pread/pwrite/swap
> > goes wrong, and that the answer would be to just not look at dimm sizes.
> 
> Hm, I'm a bit confused here ... So let me explain how swizzling on gen6+
> works with this patch:

Nah, I was the one confused.  I missed the early return in init.  Makes
sense to me now, and I agree that it should be safe to turn on
regardless, so the only issue might be that we should set swizzles on
more of the time than we actually manage to, which you already noted.

Reviewed-by: Eric Anholt <eric at anholt.net>
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