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drm/amdgpu: cleanup amdgpu_fence_activity

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The comment about the loop counter was never valid, even when you have
multiple threads this loop only runs as long as the sequence increases.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
This commit is contained in:
Christian König 2016-03-11 17:49:58 +01:00 committed by Alex Deucher
parent 22e5a2f46a
commit d9713ef6b9
1 changed files with 3 additions and 32 deletions
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35
drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
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@ -166,30 +166,8 @@ static void amdgpu_fence_schedule_fallback(struct amdgpu_ring *ring)
static bool amdgpu_fence_activity(struct amdgpu_ring *ring)
{
uint64_t seq, last_seq, last_emitted;
unsigned count_loop = 0;
bool wake = false;
/* Note there is a scenario here for an infinite loop but it's
* very unlikely to happen. For it to happen, the current polling
* process need to be interrupted by another process and another
* process needs to update the last_seq btw the atomic read and
* xchg of the current process.
*
* More over for this to go in infinite loop there need to be
* continuously new fence signaled ie amdgpu_fence_read needs
* to return a different value each time for both the currently
* polling process and the other process that xchg the last_seq
* btw atomic read and xchg of the current process. And the
* value the other process set as last seq must be higher than
* the seq value we just read. Which means that current process
* need to be interrupted after amdgpu_fence_read and before
* atomic xchg.
*
* To be even more safe we count the number of time we loop and
* we bail after 10 loop just accepting the fact that we might
* have temporarly set the last_seq not to the true real last
* seq but to an older one.
*/
last_seq = atomic64_read(&ring->fence_drv.last_seq);
do {
last_emitted = ring->fence_drv.sync_seq;
@ -200,23 +178,16 @@ static bool amdgpu_fence_activity(struct amdgpu_ring *ring)
seq |= last_emitted & 0xffffffff00000000LL;
}
if (seq <= last_seq || seq > last_emitted) {
if (seq <= last_seq || seq > last_emitted)
break;
}
/* If we loop over we don't want to return without
* checking if a fence is signaled as it means that the
* seq we just read is different from the previous on.
*/
wake = true;
last_seq = seq;
if ((count_loop++) > 10) {
/* We looped over too many time leave with the
* fact that we might have set an older fence
* seq then the current real last seq as signaled
* by the hw.
*/
break;
}
} while (atomic64_xchg(&ring->fence_drv.last_seq, seq) > seq);
if (seq < last_emitted)