From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Wilson Subject: Re: [PATCH 1/3] drm/i915: Flush the context object from the CPU caches upon switching Date: Sun, 15 Jul 2012 20:09:36 +0100 Message-ID: <1342379395_1961@CP5-2952> References: <1342352064-6749-1-git-send-email-chris@chris-wilson.co.uk> <20120715151634.GD5184@phenom.ffwll.local> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from fireflyinternet.com (smtp.fireflyinternet.com [109.228.6.236]) by gabe.freedesktop.org (Postfix) with ESMTP id 03E3D9E79D for ; Sun, 15 Jul 2012 12:09:56 -0700 (PDT) In-Reply-To: <20120715151634.GD5184@phenom.ffwll.local> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Daniel Vetter Cc: intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org On Sun, 15 Jul 2012 17:16:34 +0200, Daniel Vetter wrote: > On Sun, Jul 15, 2012 at 12:34:22PM +0100, Chris Wilson wrote: > > The issue is that we stale data in the CPU caches, when we come to > > swap-out the object, the CPU may short-circuit the reads from those > > cacheline and so corrupt the context object. > > > > Secondary, leaving the context object as being marked in the CPU write > > domain whilst on the GPU active list is a bad idea and will throw > > warnings later. > > > > Signed-off-by: Chris Wilson > > Reviewed-by: Ben Widawsky > > --- > > drivers/gpu/drm/i915/i915_gem_context.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c > > index 9ae3f2c..fd978bb 100644 > > --- a/drivers/gpu/drm/i915/i915_gem_context.c > > +++ b/drivers/gpu/drm/i915/i915_gem_context.c > > @@ -374,6 +374,13 @@ static int do_switch(struct drm_i915_gem_object *from_obj, > > if (ret) > > return ret; > > > > + /* Clear this page out of any CPU caches for coherent swap-in/out */ > > + ret = i915_gem_object_set_to_gtt_domain(to->obj, false); > > + if (ret) { > > + i915_gem_object_unpin(to->obj); > > + return ret; > > + } > > + > > Do I understand things correctly that thanks to clever use of > set_to_gtt_domain with write = false and not setting a write_domain when > moving the old context object to the active list we won't block? If so, > I'll add a short note to that effect to the commit message when merging. Worse, it was accidentally very clever. :( Definitely needs a comment and in the future a new function to dtrt intentionally! -Chris -- Chris Wilson, Intel Open Source Technology Centre