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

[Eric Anholt]

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.

Other than that, looks reasonable to me.  Might make it clear what's
going on in the commit message -- "swizzling support for snb/ivb" made
me think you were fixing up the software side of bit 6 swizzling, when
it looks like you're actually enabling bit 6 swizzling for the first
time.
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