Re: [PATCH 3/5] dma-buf: return only unsignaled fences in dma_fence_unwrap_for_each v3

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Hi Christian,

On 11.07.2022 11:57, Christian König wrote:
Hi Karolina,

Am 11.07.22 um 11:44 schrieb Karolina Drobnik:
Hi Christian,

I'm sorry for digging this one out so late.

On 06.05.2022 16:10, Christian König wrote:
dma_fence_chain containers cleanup signaled fences automatically, so
filter those out from arrays as well.

v2: fix missing walk over the array
v3: massively simplify the patch and actually update the description.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
  include/linux/dma-fence-unwrap.h | 6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h
index e7c219da4ed7..a4d342fef8e0 100644
--- a/include/linux/dma-fence-unwrap.h
+++ b/include/linux/dma-fence-unwrap.h
@@ -43,9 +43,13 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor);    * Unwrap dma_fence_chain and dma_fence_array containers and deep dive into all    * potential fences in them. If @head is just a normal fence only that one is
   * returned.
+ *
+ * Note that signalled fences are opportunistically filtered out, which
+ * means the iteration is potentially over no fence at all.
   */
  #define dma_fence_unwrap_for_each(fence, cursor, head)            \
      for (fence = dma_fence_unwrap_first(head, cursor); fence;    \
-         fence = dma_fence_unwrap_next(cursor))
+         fence = dma_fence_unwrap_next(cursor))            \
+        if (!dma_fence_is_signaled(fence))
    #endif

It looks like this particular patch affects merging Sync Fences, which is reflected by failing IGT test (igt@sw_sync)[1]. The failing subtests are:
  - sync_merge - merging different fences on the same timeline, neither
         single nor merged fences are signaled

  - sync_merge_same - merging the fence with itself on the same
         timeline, the fence didn't signal at all

  - sync_multi_timeline_wait - merging different fences on different
         timelines; the subtest checks if counting fences of
         various states works. Currently, it can only see 2
         active fences, 0 signaling (should be 2 active,
         1 signaling)

Reverting this commit on the top of drm-tip fixes the issue, but I'm not sure if it wouldn't impact other places in the code. Please let me know if I can be of any help.


Thanks for letting me know. Not sure what's going on here, but I can take a look today if time permits.

The reproduction with IGTs should be quite easy. You'll need to clone/download the IGT code and follow instructions for Building[1] the project (make sure you have meson and ninja installed):

  https://gitlab.freedesktop.org/drm/igt-gpu-tools

Once you have it up and running, go to <igt path>/build/tests, and run the subtests:

  ./sw_sync --run sync_merge
  ./sw_sync --run sync_merge_same
  ./sw_sync --run sync_multi_timeline_wait

You can run all the subtests with ./sw_sync, but I think these are the most relevant to you.

Many thanks,
Karolina

------------------
[1] - https://gitlab.freedesktop.org/drm/igt-gpu-tools#building

Do you have a description how to easy reproduce this? E.g. how to run just those specific igts?

Thanks,
Christian.


All the best,
Karolina




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