[Mesa-dev] [PATCH 1/9] drm/doc/rfc: i915 DG1 uAPI

Kenneth Graunke kenneth at whitecape.org
Wed Apr 28 17:12:12 UTC 2021

On Wednesday, April 28, 2021 9:56:25 AM PDT Jason Ekstrand wrote:
> On Wed, Apr 28, 2021 at 11:41 AM Matthew Auld <matthew.auld at intel.com> wrote:
> > Slightly orthogonal: what does Mesa do here for snooped vs LLC
> > platforms? Does it make such a distinction? Just curious.
> In Vulkan on non-LLC platforms, we only enable snooping for things
> that are going to be mapped: staging buffers, state buffers, batches,
> etc.  For anything that's not mapped (tiled images, etc.) we leave
> snooping off on non-LLC platforms so we don't take a hit from it.  In
> GL, I think it works out to be effectively the same but it's a less
> obvious decision there.
> --Jason

iris currently enables snooping on non-LLC platforms when Gallium marks
a resource as PIPE_USAGE_STAGING, which generally means it's going to be
mapped and "fast CPU access" is desired.  Most buffers are not snooped.

I don't believe i965 uses snooping at all, surprisingly.

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