On Tue, 2014-08-26 at 15:44 -0700, Kenneth Graunke wrote: > On Friday, August 22, 2014 12:59:57 PM Samuel Iglesias Gonsálvez wrote: > > On Thu, 2014-08-14 at 14:28 +0200, Iago Toral Quiroga wrote: > > [...] > > > At this point I'd like to hear suggestions for things we could try next > > > to confirm whether this is a hardware problem or a driver problem, or, > > > if we agree that this is enough evidence that this must be a hardware > > > problem, how we can limit its impact, starting, probably, by rewriting > > > the piglit test so that we don't alter its purpose but avoid the hang on > > > gen6. We should also discuss if there is a way to work around this > > > problem so that at least developers running into it (as unlikely as that > > > may be) don't hang their systems. > > > > > > I am going to be on holidays starting tomorrow and will have difficult > > > and limited Internet access for the most part, but Samuel (in the CC) > > > will be available next week to try any suggestions you may have. > > > > As Iago said, I'm available for trying any suggestions you may have. > > > > I'm wondering if you need more information about the issue or if I can > > run more tests in order to confirm/discard this is a HW problem and the > > next steps to follow. > > > > Best regards, > > > > Sam > > I just came across an interesting looking errata... > > From the Sandybridge PRM, Volume 2 Part 1, Section 5.5.1 "Partial Object > Removal": > > "An object is considered ‘partial’ if the last vertex of the primitive > topology > is encountered (i.e., PrimEnd is set) before a complete set of vertices for > that object have been received. Given that only LINESTRIP and TRISTRIP > primitive > types are subject to CLIP unit partial object removal, the only supported > cases > of partial objects are 1-vertex LINESTRIPs and 1 or 2-vertex TRISTRIPs. > > [errata DevSNB]: Possible hang if final output from GS kernel is 2 vertex > triangle. If it is possible for the final output from GS kernel to be a 2 > vertex triangle, then have the GS kernel always output an extra single vertex > triangle as the final output." > > Do you think this could be related? It's a SNB specific hang closely tied to > triangle strips, which sounds promising, but the symptoms don't sound quite > right either... >
As Iago reported, the issue is specific to glDrawElements(), while glDrawArrays() is not affected. If the errata was the source of the issue, I understand that it should affect both rendering commands, am I wrong? However it is interesting to know this SNB's errata because our GS patches don't take into account that the final output from GS kernel might be 2 vertex a triangle and that could produce another GPU hang. Thanks! Sam
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