drm/radeon: restore hardware polling in fence_is_signaled to fix performance regression

Commit 527ba26e50ec ("drm/radeon: delete radeon_fence_process in
is_signaled, no deadlock") removed the hardware polling from
radeon_fence_is_signaled() to fix a self-deadlock caused by
wake_up_all(&rdev->fence_queue) being called with the fence queue
lock held.

However, removing the polling entirely causes significant performance
regression (e.g. glxgears FPS drop) because the fence signaled check
becomes purely passive — it only reads the cached last_seq without
probing the GPU, so completed GPU work is not detected in time,
causing unnecessary CPU stalls in sync-heavy workloads.

Fix this by calling radeon_fence_activity() directly instead of
radeon_fence_process(). radeon_fence_activity() reads the hardware
fence counter and updates last_seq via atomic ops without calling
wake_up_all(), thus avoiding the deadlock while restoring timely
fence detection.

Fixes: 527ba26e50ec ("drm/radeon: delete radeon_fence_process in is_signaled, no deadlock")
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Wang Jiang <jiangwang@kylinos.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit f59ad4cca219c7fdf934f712c5860ec5f5900fd7)
Cc: stable@vger.kernel.org

diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
index 02a40e4750c7dd0b7adacd8a145c8d5f0e0d0e49..299865569252d7765dc3a2e79b4f7df10eec3f18 100644 (file)
--- a/drivers/gpu/drm/radeon/radeon_fence.c
+++ b/drivers/gpu/drm/radeon/radeon_fence.c
@@ -360,6 +360,13 @@ static bool radeon_fence_is_signaled(struct dma_fence *f)
        if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq)
                return true;
 
+       if (down_read_trylock(&rdev->exclusive_lock)) {
+               radeon_fence_activity(rdev, ring);
+               up_read(&rdev->exclusive_lock);
+
+               if (atomic64_read(&rdev->fence_drv[ring].last_seq) >= seq)
+                       return true;
+       }
        return false;
 }