From: Chris Wilson <chris@chris-wilson.co.uk>
To: Eric Anholt <eric@anholt.net>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 4/6] drm/i915: Add an interface to dynamically change the cache level
Date: Thu, 31 Mar 2011 08:29:31 +0100 [thread overview]
Message-ID: <b7da2f$qu1e42@fmsmga001.fm.intel.com> (raw)
In-Reply-To: <87aagcb7vc.fsf@pollan.anholt.net>
On Wed, 30 Mar 2011 14:45:11 -0700, Eric Anholt <eric@anholt.net> wrote:
> On Wed, 30 Mar 2011 18:16:11 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > On Wed, 30 Mar 2011 09:59:55 -0700, Eric Anholt <eric@anholt.net> wrote:
> > > And what about a CPU write through the GTT?
> >
> > Even on SNB these are still UC. And we should try hard not to, as the
> > specs give dire warnings about writing to snooped PTEs through the GTT.
> > (Since we will bypass the caches with the write, aiui, and cause
> > confusion.)
>
> Oh, wow. That's really bad. Reject this series if so.
I plucked that tidbit out of the specs for the BLT engine, which has not
been rigorously updated since gen2... Though don't we also encounter a few
subtleties with movnta (__copy_from_user_nocache_nozero from pwrite) and
data in cachelines?
But it is something that I worry about given my desire to start mapping
user pages and using the BLT engine for C to UC transfers.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
next prev parent reply other threads:[~2011-03-31 7:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-29 23:59 reduced LLC caching series Eric Anholt
2011-03-29 23:59 ` [PATCH 1/6] drm/i915: Rename agp_type to cache_level Eric Anholt
2011-03-29 23:59 ` [PATCH 2/6] drm/i915: Mark the cursor and the overlay as being part of the display planes Eric Anholt
2011-03-29 23:59 ` [PATCH 3/6] drm/i915: Do not clflush snooped objects Eric Anholt
2011-03-29 23:59 ` [PATCH 4/6] drm/i915: Add an interface to dynamically change the cache level Eric Anholt
2011-03-30 7:09 ` Chris Wilson
2011-03-30 16:59 ` Eric Anholt
2011-03-30 17:16 ` Chris Wilson
2011-03-30 21:45 ` Eric Anholt
2011-03-31 7:29 ` Chris Wilson [this message]
2011-03-31 20:10 ` Eric Anholt
2011-03-29 23:59 ` [PATCH 5/6] drm/i915: Use the uncached domain for the display planes v2 Eric Anholt
2011-03-29 23:59 ` [PATCH 6/6] drm/i915: Use the LLC mode on gen6 for everything but display Eric Anholt
2011-03-30 22:35 ` reduced LLC caching series Michael Larabel
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