On Tue, Jul 25, 2017 at 02:55:14PM +0800, zhoucm1 wrote: > > > On 2017年07月25日 14:50, Daniel Vetter wrote: > > On Tue, Jul 25, 2017 at 02:16:55PM +0800, zhoucm1 wrote: > > > > > > On 2017年07月24日 19:57, Daniel Vetter wrote: > > > > On Mon, Jul 24, 2017 at 11:51 AM, Christian König > > > > <deathsimple@xxxxxxxxxxx> wrote: > > > > > Am 24.07.2017 um 10:33 schrieb Daniel Vetter: > > > > > > On Fri, Jul 21, 2017 at 06:20:01PM +0200, Christian König wrote: > > > > > > > From: Christian König <christian.koenig@xxxxxxx> > > > > > > > > > > > > > > With hardware resets in mind it is possible that all shared fences are > > > > > > > signaled, but the exlusive isn't. Fix waiting for everything in this > > > > > > > situation. > > > > > > How did you end up with both shared and exclusive fences on the same > > > > > > reservation object? At least I thought the point of exclusive was that > > > > > > it's exclusive (and has an implicit barrier on all previous shared > > > > > > fences). Same for shared fences, they need to wait for the exclusive one > > > > > > (and replace it). > > > > > > > > > > > > Is this fallout from the amdgpu trickery where by default you do all > > > > > > shared fences? I thought we've aligned semantics a while back ... > > > > > No, that is perfectly normal even for other drivers. Take a look at the > > > > > reservation code. > > > > > > > > > > The exclusive fence replaces all shared fences, but adding a shared fence > > > > > doesn't replace the exclusive fence. That actually makes sense, cause when > > > > > you want to add move shared fences those need to wait for the last exclusive > > > > > fence as well. > > > > Hm right. > > > > > > > > > Now normally I would agree that when you have shared fences it is sufficient > > > > > to wait for all of them cause those operations can't start before the > > > > > exclusive one finishes. But with GPU reset and/or the ability to abort > > > > > already submitted operations it is perfectly possible that you end up with > > > > > an exclusive fence which isn't signaled and a shared fence which is signaled > > > > > in the same reservation object. > > > > How does that work? The batch(es) with the shared fence are all > > > > supposed to wait for the exclusive fence before they start, which > > > > means even if you gpu reset and restart/cancel certain things, they > > > > shouldn't be able to complete out of order. > > > Hi Daniel, > > > > > > Do you mean exclusive fence must be signalled before any shared fence? Where > > > could I find this restriction? > > Yes, Christian also described it above. Could be that we should have > > better kerneldoc to document this ... > Is that a known assumption? if that way, it doesn't matter even that we > always wait exclusive fence, right? Just one more line checking. The problem is that amdgpu breaks that assumption over gpu reset, and that might have implications _everywhere_, not just in this code here. Are you sure this case won't pull the i915 driver over the table when sharing dma-bufs with it? Did you audit the code (plus all the other drivers too ofc). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
