Re: [PATCH 1/3] drm/i915: Stop putting GGTT VMA at the head of the list

From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
	Intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 1/3] drm/i915: Stop putting GGTT VMA at the head of the list
Date: Thu, 4 Dec 2014 11:54:29 +0100	[thread overview]
Message-ID: <20141204105429.GL32117@phenom.ffwll.local> (raw)
In-Reply-To: <20141204094811.GG25773@nuc-i3427.alporthouse.com>

On Thu, Dec 04, 2014 at 09:48:11AM +0000, Chris Wilson wrote:
> On Wed, Dec 03, 2014 at 02:59:24PM +0000, Tvrtko Ursulin wrote:
> > From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > 
> > Multiple GGTT VMAs per object will be introduced in the near future which will
> > make it impossible to guarantee normal GGTT view is at the head of the list.
> > 
> > Purpose of this patch is to break this assumption straight away so any
> > potential hidden assumptions in the code base can be bisected to this
> > simple patch.
> 
> No, please don't. The rationale for putting ggtt first is because it
> puts the one vma that every object is likely to use at the front, and
> makes it also the first in the list for debugging.

With hindsight I think this was just premature optimization (and way too
many obj->vma lookups to boot). Imo we should just fix the remaining
spurious obj->vma lookups we have and if there's still a problem then we
need to have actual benchmark data or profiles to support this trick.

Hence I pulled this patch in, thanks.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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