On Mon, Jan 20, 2014 at 9:30 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, Jan 20, 2014 at 10:17:36AM +0000, Chris Wilson wrote: >> On older generations (gen2, gen3) the GPU requires fences for many >> operations, such as blits. The display hardware also requires fences for >> scanouts and this leads to a situation where an arbitrary number of >> fences may be pinned by old scanouts following a pageflip but before we >> have executed the unpin workqueue. This is unpredictable by userspace >> and leads to random EDEADLK when submitting an otherwise benign >> execbuffer. However, we can detect when we have an outstanding flip and >> so cause userspace to wait upon their completion before finally >> declaring that the system is starved of fences. This is really no worse >> than forcing the GPU to stall waiting for older execbuffer to retire and >> release their fences before we can reallocate them for the next >> execbuffer. >> >> v2: move the test for a pending fb unpin to a common routine for >> later reuse during eviction >> >> Reported-and-tested-by: dimon@xxxxxxx >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73696 > Testcase: i-g-t/kms_flip/flip-vs-fences >> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > The testcase is only for the trivial reproduction scenario, not the more > sporadic situation involving a slightly hungry workqueue, but it is > enough to demonstrate the issue and the effectiveness of the simple > workaround (for typical userspace). Testcase convinced me, this is better than status quo ;-) I guess I'll add a short comment though when merging that busy-looping through EAGAIN is a but un-neat. Jon, since this ties into the evict_something fun we've had last year can you please review this patch plus the follow-up one? Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
