On Thu, Dec 04, 2014 at 10:30:30AM +0000, Tvrtko Ursulin wrote: > > On 12/04/2014 10:17 AM, Chris Wilson wrote: > >On Thu, Dec 04, 2014 at 10:02:19AM +0000, Tvrtko Ursulin wrote: > >> > >>On 12/04/2014 09:48 AM, Chris Wilson wrote: > >>>On Wed, Dec 03, 2014 at 02:59:24PM +0000, Tvrtko Ursulin wrote: > >>>>From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > >>>> > >>>>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. > >> > >>This came from talking with Daniel, but I don't understand why every > >>object is likely to have a GGTT mapping? > > > >Because the userspace usage pattern is such that it is typical that > >every object is accessed through the GTT at some point in its life. > > > >It's actually becoming less so as we use alternative mmappings, but it > >will remain so for quite some time yet. > > > >>With multiple GGTT views it may happen that only single GGTT VMA > >>exists in the list but it is not the one current code would expect. > >>So the idea was to break that to flesh out any potential hidden > >>assumptions in the code. (I did not find any by just looking > >>though.) > >> > >>What kind of debugging you have in mind, error capture? Or actually > >>inspecting memory of a live kernel? > > > >Error capture inspection of memory of a live kernel. > > So personally you don't think it should be of any concern if a GGTT > VMA is at the head of the list, but it is not the same GGTT VMA > which you would find there in majority of cases? Actually, regarding error capture it is sorting of the vm list that is important - so a different list. I am still confused about why having different GGTT views makes it difficult putting the normal GGTT vm first. I would very much like the standard GGTT view remain first, and I would actually like the MRU ppgtt last (so that the two most common uses are easily found). -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
