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). -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
