[Intel-gfx] [PATCH] drm/i915: Wait for completion of pending flips when starved of fences

[Daniel Vetter]

On Sun, Jan 19, 2014 at 10:20 PM, Chris Wilson <chris at chris-wilson.co.uk> 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.
>
> Reported-and-tested-by: dimon at gmx.net
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73696
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

New subtest for kms_flip which submits such a blt buffer while a
pageflip is still pending? Also there's a certain chance we'll starve
the unpin work, similar to the issues around flushing the unpin work
in our pageflip implementation. Finally I think this should be
encapsulated into a little helper to be used in evict_something.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch