Intel DRM driver for SNB
benjamin.segovia at intel.com
Tue Dec 14 15:34:12 PST 2010
Also, does i915 actually use uncacheable pages for CPU memory? When going to cpu -> gpu domain for gem buffers, I saw explicit clflush but nothing seems to show use of uncacheable pages. Did I miss something?
From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
Sent: Tuesday, December 14, 2010 2:00 AM
To: Segovia, Benjamin; Segovia, Benjamin; Zhenyu Wang
Subject: RE: Intel DRM driver for SNB
On Mon, 13 Dec 2010 20:32:42 -0800, "Segovia, Benjamin" <benjamin.segovia at intel.com> wrote:
> To be more explicit, my concern is that I read that Chris Wilson proposed a patch preventing the VM to swap pages still in GTT. I did not see any trace of this patch in the main line yet.
No, because the mm maintainers corrected me by pointing out that a page
will not be swapped whilst a reference is held and it remains off the zone
LRU lists. (That said there remains a persistent nagging doubt that
something smells fishy...)
But as for what you want to do, it is possible with the current module.
However as it deliberately evades the minimal security provisions we have,
it should only be done from a privileged application.
In principle, there should be sufficient knowledge within the kernel to
maintain coherency for you. I'm interested in knowing how you plan to
manage coherency to make sure we have not missed something. (Give or take
the fixes for completely handing coherency of uncached/cached CPU
With ppGTT, we can be much more permissive and allow individual apps to
reserve portions of the GTT without impacting other users of the system.
Chris Wilson, Intel Open Source Technology Centre
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