On 2021-08-26 12:55 a.m., Liu, Monk wrote:
[AMD Official Use Only]
But for timer pending case (common case) your mod_delayed_work will effectively do exactly the same if you don't use per job TTLs - you mod it to sched->timeout value which resets the pending timer to again count from 0.
Ny patch will only modify the timer (restart it , actually) when the heading job is signaled, which means on HW ring the next job is just about start processing.
Not sure this is always true, see this specific test we added long ago
https://gitlab.freedesktop.org/mesa/drm/-/commit/bc21168fa924d3fc4a000492e861f50a1a135b25
AFAIK a ring doesn't have strict serialization of processing jobs one
after another, especially when 2 jobs are scheduled from different
contexts like in the example above
which means that in this case the second job might be well into
execution for some time when the first finish and restarts the TDR timer
from scratch.
If the job is not signaled (your common case) the timer is still not touched at all ...
I just wonder why we stopped using per job TDR timers in the first place ? Isn't the simplest way to count accurate timeouts for each job is to actually measure the timeouts for each job separately ?
I'm not sure if Christian can recall something, and I believe it is due to some limitations we found (or some race issue like two job on the same scheduler TO in the same time, which is probably if they are scheduled to the ring almost in the same timeframe)
Anyway I have a V3 version patch, please take a look, it looks working for me
Will take a look tomorrow
Andrey
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
-----Original Message-----
From: Grodzovsky, Andrey <Andrey.Grodzovsky@xxxxxxx>
Sent: Thursday, August 26, 2021 11:05 AM
To: Liu, Monk <Monk.Liu@xxxxxxx>; Christian König <ckoenig.leichtzumerken@xxxxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] drm/sched: fix the bug of time out calculation(v2)
On 2021-08-25 10:31 p.m., Liu, Monk wrote:
[AMD Official Use Only]
Hi Andrey
I'm not quite sure if I read you correctly
Seems to me you can only do it for empty pending list otherwise you risk cancelling a legit new timer that was started by the next job or not restarting timer at all since your timer was still pending when next job tried to start it again (the common case).
I don't understand above sentence, from my understanding for the
common case, if the timer is pending, the cancel_delay_work in
beginning will cancel it and then we will get to the line of "queue
timeout for next job" since the heading job is not signaled (align
with the timer is pending), then the timer will be restarted (for the
next job)
Ignore it, i realized from looking that i missed the timer restart in then end of drm_sched_get_cleanup_job or the alternative one in drm_sched_main
And above sequence is actually wrong to me, because we cancelled a
pending timer and restart the timer for the scheduler that its heading
job is still running there, the whole counting is repeated from zero
and inaccurate at all
But for timer pending case (common case) your mod_delayed_work will effectively do exactly the same if you don't use per job TTLs - you mod it to sched->timeout value which resets the pending timer to again count from 0.
I just wonder why we stopped using per job TDR timers in the first place ? Isn't the simplest way to count accurate timeouts for each job is to actually measure the timeouts for each job separately ?
Andrey
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
-----Original Message-----
From: Grodzovsky, Andrey <Andrey.Grodzovsky@xxxxxxx>
Sent: Thursday, August 26, 2021 2:20 AM
To: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>; Liu, Monk
<Monk.Liu@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel
<dri-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] drm/sched: fix the bug of time out
calculation(v2)
On 2021-08-25 8:11 a.m., Christian König wrote:
No, this would break that logic here.
See drm_sched_start_timeout() can be called multiple times, this is
intentional and very important!
The logic in queue_delayed_work() makes sure that the timer is only
started once and then never again.
All we need to take care of is to cancel_delayed_work() when we know
that the job is completed.
Seems to me you can only do it for empty pending list otherwise you risk cancelling a legit new timer that was started by the next job or not restarting timer at all since your timer was still pending when next job tried to start it again (the common case).
For non empty pending list you have to adjust the currently active TDR's timer from your's job TTL to TTL to the next job after you or just restart it as Monk does it here which prolongs the timeout more then required but still ok i guess.
What about returning to the old scheme of timer sched_work per job so
each job has it's own timer and we don't share it and everything is
precise for each job, using the locking scheme we already have today
the actual TDR handler will execute only once while all the other
arising from the guilty job hang will be rejected (for amdgpu, for
other drivers it probably requires same locking or we can move this to
the scheduler layer)
Andrey
This here works as intended as far as I can see and if you start to
use mod_delayed_work() you actually break it.
Regards,
Christian.
Am 25.08.21 um 14:01 schrieb Liu, Monk:
[AMD Official Use Only]
I think we should remove the cancel_delayed_work() in the beginning
of the cleanup_job().
Because by my patch the "mode_delayed_work" in cleanup_job is
already doing its duty to retrigger the TO timer accordingly
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
-----Original Message-----
From: Liu, Monk
Sent: Wednesday, August 25, 2021 7:55 PM
To: 'Christian König' <ckoenig.leichtzumerken@xxxxxxxxx>;
amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Subject: RE: [PATCH] drm/sched: fix the bug of time out
calculation(v2)
[AMD Official Use Only]
The timeout started by queue_delayed_work() in
drm_sched_start_timeout() is paired with the cancel_delayed_work()
in drm_sched_get_cleanup_job().
No that's wrong, see that when we are in cleanup_job(), assume we do
not have timeout on this sched (we are just keep submitting new jobs
to this sched), Then the work_tdr is cancelled, and then we get the
heading job, and let's assume the job is not signaled, then we run
to the "queue timeout for next job" thus drm_sched_start_timeout()
is called, so this heading job's TO timer is actually retriggered ...
which is totally wrong.
With my patch the timer is already retriggered after previous JOB
really signaled.
Can you be more specific on the incorrect part ?
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
-----Original Message-----
From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
Sent: Wednesday, August 25, 2021 2:32 PM
To: Liu, Monk <Monk.Liu@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH] drm/sched: fix the bug of time out
calculation(v2)
Well NAK to that approach. First of all your bug analyses is incorrect.
The timeout started by queue_delayed_work() in
drm_sched_start_timeout() is paired with the cancel_delayed_work()
in drm_sched_get_cleanup_job().
So you must have something else going on here.
Then please don't use mod_delayed_work(), instead always cancel it
and restart it.
Regards,
Christian.
Am 25.08.21 um 06:14 schrieb Monk Liu:
the original logic is wrong that the timeout will not be retriggerd
after the previous job siganled, and that lead to the scenario that
all jobs in the same scheduler shares the same timeout timer from
the very begining job in this scheduler which is wrong.
we should modify the timer everytime a previous job signaled.
v2:
further cleanup the logic, and do the TDR timer cancelling if the
signaled job is the last one in its scheduler.
Signed-off-by: Monk Liu <Monk.Liu@xxxxxxx>
---
drivers/gpu/drm/scheduler/sched_main.c | 29
++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index a2a9536..8c102ac 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -305,8 +305,17 @@ static void drm_sched_job_begin(struct
drm_sched_job *s_job)
struct drm_gpu_scheduler *sched = s_job->sched;
spin_lock(&sched->job_list_lock);
- list_add_tail(&s_job->list, &sched->pending_list);
- drm_sched_start_timeout(sched);
+ if (list_empty(&sched->pending_list)) {
+ list_add_tail(&s_job->list, &sched->pending_list);
+ drm_sched_start_timeout(sched);
+ } else {
+ /* the old jobs in pending list are not finished yet
+ * no need to restart TDR timer here, it is already
+ * handled by drm_sched_get_cleanup_job
+ */
+ list_add_tail(&s_job->list, &sched->pending_list);
+ }
+
spin_unlock(&sched->job_list_lock);
}
@@ -693,17 +702,22 @@ drm_sched_get_cleanup_job(struct
drm_gpu_scheduler *sched)
if (job && dma_fence_is_signaled(&job->s_fence->finished))
{
/* remove job from pending_list */
list_del_init(&job->list);
+
/* make the scheduled timestamp more accurate */
next = list_first_entry_or_null(&sched->pending_list,
typeof(*next), list);
- if (next)
+ if (next) {
+ /* if we still have job in pending list we need modify
the TDR timer */
+ mod_delayed_work(system_wq, &sched->work_tdr,
sched->timeout);
next->s_fence->scheduled.timestamp =
job->s_fence->finished.timestamp;
+ } else {
+ /* cancel the TDR timer if no job in pending list */
+ cancel_delayed_work(&sched->work_tdr);
+ }
} else {
job = NULL;
- /* queue timeout for next job */
- drm_sched_start_timeout(sched);
}
spin_unlock(&sched->job_list_lock);
@@ -791,11 +805,8 @@ static int drm_sched_main(void *param)
(entity =
drm_sched_select_entity(sched)))
||
kthread_should_stop());
- if (cleanup_job) {
+ if (cleanup_job)
sched->ops->free_job(cleanup_job);
- /* queue timeout for next job */
- drm_sched_start_timeout(sched);
- }
if (!entity)
continue;
