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

[2564278112]

From: Wang Jiang <jiangwang@xxxxxxxxxx>

Commit 9eb00b5f5697b ("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: 9eb00b5f5697b ("drm/radeon: delete radeon_fence_process in is_signaled, no deadlock")
Signed-off-by: Wang Jiang <jiangwang@xxxxxxxxxx>
---
 drivers/gpu/drm/radeon/radeon_fence.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
index 02a40e4750c7..299865569252 100644
--- 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;
 }
 
-- 
2.25.1