Re: [PATCH] drm/i915: Mark CPU cache as dirty when used for rendering

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

On Mon, Nov 07, 2016 at 03:46:28PM +0000, Chris Wilson wrote:
> On LLC, or even snooped, machines rendering via the GPU ends up in the CPU
> cache. This cacheline dirt also needs to be flushed to main memory when
> moving to an incoherent domain, such as the display's scanout engine.
> Mostly, this happens because either the object is marked as dirty from
> its first use or is avoided by setting the object into the display
> domain from the start.
> 
> Fixes: 0f71979ab7fb ("drm/i915: Performed deferred clflush inside set-cache-level")
> References: https://bugs.freedesktop.org/show_bug.cgi?id=95414
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> ---
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 30f6eb516ca3..30b684fecf09 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1282,6 +1282,7 @@ void i915_vma_move_to_active(struct i915_vma *vma,
>  
>  		/* update for the implicit flush after a batch */
>  		obj->base.write_domain &= ~I915_GEM_GPU_DOMAINS;
> +		obj->cache_dirty |= obj->cache_level != I915_CACHE_NONE;

I915_CACHE_WT shouldn't dirty the cache either, so could be excluded
as well.

Everything else makes sense
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  	}
>  
>  	if (flags & EXEC_OBJECT_NEEDS_FENCE)
> -- 
> 2.10.2

-- 
Ville Syrjälä
Intel OTC