[Intel-gfx] [PATCH v2 2/2] drm/i915/bxt: Fix inadvertent CPU snooping due to incorrect MOCS config

[Chris Wilson]

On Tue, Apr 26, 2016 at 03:44:22PM +0300, Imre Deak wrote:
> Setting a write-back cache policy in the MOCS entry definition also
> implies snooping, which has a considerable overhead. This is
> unexpected for a few reasons:
> - From user-space's point of view since it didn't want a coherent
>   surface (it didn't set the buffer as such via the set caching IOCTL).

To put it into context, this is the point of MOCS. Userspace can
configure its buffer access without having to tell the kernel to do a
synchronous (i.e. stalling and is slow) update of the PTE.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre