Am 12.06.2013 12:26, schrieb Michel Dänzer:
On Die, 2013-06-11 at 16:23 -0700, Andy Lutomirski wrote:
If the device is idle for over ten seconds, then the next attempt to do anything can race with the lockup detector and cause a bogus lockup to be detected.
Oddly, the situation is well-described in the lockup detector's comments and a fix is even described. This patch implements that fix (and corrects some typos in the description).
My system has been stable for about a week running this code. Without this, my screen would go blank every now and then and, when it came back, everything would be remarkably slow (the latter is a separate bug).
Signed-off-by: Andy Lutomirski luto@amacapital.net
[...]
diff --git a/drivers/gpu/drm/radeon/radeon_ring.c b/drivers/gpu/drm/radeon/radeon_ring.c index 1ef5eaa..fb7b3ea 100644 --- a/drivers/gpu/drm/radeon/radeon_ring.c +++ b/drivers/gpu/drm/radeon/radeon_ring.c @@ -547,12 +547,12 @@ void radeon_ring_lockup_update(struct radeon_ring *ring)
- have CP rptr to a different value of jiffies wrap around which will force
- initialization of the lockup tracking informations.
- A possible false positivie is if we get call after while and last_cp_rptr ==
- the current CP rptr, even if it's unlikely it might happen. To avoid this
- if the elapsed time since last call is bigger than 2 second than we return
- false and update the tracking information. Due to this the caller must call
- radeon_ring_test_lockup several time in less than 2sec for lockup to be reported
- the fencing code should be cautious about that.
- A possible false positive is if we get called after a while and
- last_cp_rptr == the current CP rptr, even if it's unlikely it might
- happen. To avoid this if the elapsed time since the last call is bigger
- than 2 second then we return false and update the tracking
- information. Due to this the caller must call radeon_ring_test_lockup
- more frequently than once every 2s when waiting.
Is it guaranteed that radeon_ring_test_lockup will be called more often than every 2s when waiting? If not, this change might prevent a real lockup from being detected?
Either way, I wonder if there might not be a simpler solution to the problem, e.g. by updating last_activity when submitting commands to a previously empty ring.
If I remember correctly that's exactly what I used to do when creating radeon_ring_test_lockup, and now I'm really wondering why that stuff isn't there any more.
Anyway the problem you describe should only happen very very rarely in case of a wraparound, so I'm pretty sure that we have a different problem that's just masked by that patch.
Christian.