drm/i915: Use discardable buffers for rings
authorChris Wilson <chris@chris-wilson.co.uk>
Thu, 20 Apr 2017 10:17:09 +0000 (11:17 +0100)
committerChris Wilson <chris@chris-wilson.co.uk>
Thu, 20 Apr 2017 11:00:32 +0000 (12:00 +0100)
commit2d6c4c84230df9ff99b626b52b11049e449632c9
tree0616399a9f9971ef6bfbd9ae07bb50904191c742
parent2310b3c952c5dc56c2e08f71b907b8e23ab3270d
drm/i915: Use discardable buffers for rings

The contents of a ring are only valid between HEAD and TAIL, when the
ring is idle (HEAD == TAIL) we can simply let the pages go under memory
pressure if they are not pinned by an active context. Any new content
will be written after HEAD and so the ring will again be valid between
HEAD and TAIL, everything outside can be discarded.

Note that we take care of ensuring that we do not reset the HEAD
backwards following a GPU hang on an idle ring.

The same precautions are what enable us to use stolen memory for rings.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170420101709.27250-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
drivers/gpu/drm/i915/intel_ringbuffer.c