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dma-buf: add dma_fence_timestamp helper 

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: 1774baa64f ("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
This commit is contained in:
Christian König 2023-09-08 10:27:23 +02:00
parent d59e75eef5
commit b83ce9cb4a
4 changed files with 27 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
drivers/dma-buf/dma-fence-unwrap.c
View File

@ -76,16 +76,11 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
if (!dma_fence_is_signaled(tmp)) {
++count;
} else if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
&tmp->flags)) {
if (ktime_after(tmp->timestamp, timestamp))
timestamp = tmp->timestamp;
} else {
/*
* Use the current time if the fence is
* currently signaling.
*/
timestamp = ktime_get();
ktime_t t = dma_fence_timestamp(tmp);
if (ktime_after(t, timestamp))
timestamp = t;
}
}
}

7
drivers/dma-buf/sync_file.c
View File

@ -268,12 +268,9 @@ static int sync_fill_fence_info(struct dma_fence *fence,
sizeof(info->driver_name));
info->status = dma_fence_get_status(fence);
while (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
cpu_relax();
info->timestamp_ns =
test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags) ?
ktime_to_ns(fence->timestamp) :
dma_fence_is_signaled(fence) ?
ktime_to_ns(dma_fence_timestamp(fence)) :
ktime_set(0, 0);
return info->status;

2
drivers/gpu/drm/scheduler/sched_main.c
View File

@ -929,7 +929,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
if (next) {
next->s_fence->scheduled.timestamp =
job->s_fence->finished.timestamp;
dma_fence_timestamp(&job->s_fence->finished);
/* start TO timer for next job */
drm_sched_start_timeout(sched);
}

19
include/linux/dma-fence.h
View File

@ -568,6 +568,25 @@ static inline void dma_fence_set_error(struct dma_fence *fence,
fence->error = error;
}
/**
* dma_fence_timestamp - helper to get the completion timestamp of a fence
* @fence: fence to get the timestamp from.
*
* After a fence is signaled the timestamp is updated with the signaling time,
* but setting the timestamp can race with tasks waiting for the signaling. This
* helper busy waits for the correct timestamp to appear.
*/
static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
{
if (WARN_ON(!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)))
return ktime_get();
while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
cpu_relax();
return fence->timestamp;
}
signed long dma_fence_wait_timeout(struct dma_fence *,
bool intr, signed long timeout);
signed long dma_fence_wait_any_timeout(struct dma_fence **fences,