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@intel.com> wrote:
[snip]
> > 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.

--Ken