One alternative to the fix Christian proposed in
https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@amd.com/
is to replace the rather complex open coded sorting loops with the kernel
standard sort followed by a context squashing pass.
Proposed advantage of this would be readability but one concern Christian
raised was that there could be many fences, that they are typically mostly
sorted, and so the kernel's heap sort would be much worse by the proposed
algorithm.
I had a look running some games and vkcube to see what are the typical
number of input fences. Tested scenarios:
1) Hogwarts Legacy under Gamescope
450 calls per second to __dma_fence_unwrap_merge.
Percentages per number of fences buckets, before and after checking for
signalled status, sorting and flattening:
N Before After
0 0.91%
1 69.40%
2-3 28.72% 9.4% (90.6% resolved to one fence)
4-5 0.93%
6-9 0.03%
10+
2) Cyberpunk 2077 under Gamescope
1050 calls per second, amounting to 0.01% CPU time according to perf top.
N Before After
0 1.13%
1 52.30%
2-3 40.34% 55.57%
4-5 1.46% 0.50%
6-9 2.44%
10+ 2.34%
3) vkcube under Plasma
90 calls per second.
N Before After
0
1
2-3 100% 0% (Ie. all resolved to a single fence)
4-5
6-9
10+
In the case of vkcube all invocations in the 2-3 bucket were actually
just two input fences.
From these numbers it looks like the heap sort should not be a
disadvantage, given how the dominant case is <= 2 input fences which heap
sort solves with just one compare and swap. (And for the case of one input
fence we have a fast path in the previous patch.)
A complementary possibility is to implement a different sorting algorithm
under the same API as the kernel's sort() and so keep the simplicity,
potentially moving the new sort under lib/ if it would be found more
widely useful.
v2:
* Hold on to fence references and reduce commentary. (Christian)
* Record and use latest signaled timestamp in the 2nd loop too.
* Consolidate zero or one fences fast paths.
v3:
* Reverse the seqno sort order for a simpler squashing pass. (Christian)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Friedrich Vock <friedrich.vock@gmx.de>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: <stable@vger.kernel.org> # v6.0+
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursulin@igalia.com
Release all fence references if the output dma-fence-array could not be
allocated.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3")
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Friedrich Vock <friedrich.vock@gmx.de>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: <stable@vger.kernel.org> # v6.0+
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-2-tursulin@igalia.com
When a fence signals there is a very small race window where the timestamp
isn't updated yet. sync_file solves this by busy waiting for the
timestamp to appear, but on other ocassions didn't handled this
correctly.
Provide a dma_fence_timestamp() helper function for this and use it in
all appropriate cases.
Another alternative would be to grab the spinlock when that happens.
v2 by teddy: add a wait parameter to wait for the timestamp to show up, in case
the accurate timestamp is needed and/or the timestamp is not based on
ktime (e.g. hw timestamp)
v3 chk: drop the parameter again for unified handling
Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 1774baa64f93 ("drm/scheduler: Change scheduled fence track v2")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
CC: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20230929104725.2358-1-christian.koenig@amd.com
Some Android CTS is testing if the signaling time keeps consistent
during merges.
v2: use the current time if the fence is still in the signaling path and
the timestamp not yet available.
v3: improve comment, fix one more case to use the correct timestamp
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630120041.109216-1-christian.koenig@amd.com
This reverts commit 8f61973718485f3e89bc4f408f929048b7b47c83.
It turned out that this is not correct. Especially the sync_file info
IOCTL needs to see even signaled fences to correctly report back their
status to userspace.
Instead add the filter in the merge function again where it makes sense.
Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Karolina Drobnik <karolina.drobnik@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220712102849.1562-1-christian.koenig@amd.com
Introduce a dma_fence_unwrap_merge() macro which allows to unwrap fences
which potentially can be containers as well and then merge them back
together into a flat dma_fence_array.
v2: rename the function, add some more comments about how the wrapper is
used, move filtering of signaled fences into the unwrap iterator,
add complex selftest which covers more cases.
v3: fix signaled fence filtering once more
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518135844.3338-5-christian.koenig@amd.com
