On 2021-02-26 10:56 p.m., Liu, Monk wrote:
[AMD Official Use Only - Internal Distribution Only]
H Andrey
The scenario I hit here is not the one you mentioned, let me explain
it with more details by another much easier understood example:
Consider ring you have a job1 on KCQ, but the timeout of KCQ is 60
seconds (just for example)
You also have a job2 on GFX ring, and the timeout of GFX is 2 seconds
We submit job1 first, and assume job1 have bug and it will cause
shader hang very very soon
After 10 seconds we submit job2, since KCQ have 60 seconds to report
TDR thus SW know nothing about the engine already hang
So gfx job hangs because it has a dependency on buggy compute job which
already is hanging ?
After 2 seconds we got TDR report from job2 on GFX ring,
sched_job_timeout() think the leading job of GFX ring is the black
sheep so it is deleted from the mirror list
But in fact this job1 is innocent, and we should insert it back after
recovery , and due to it was already deleted this innocent job’s
context/process is really harmed
I am still missing something - we don't ever delete bad jobs or any jobs
until they are signaled, we reinsert the bad job back into mirror list
in drm_sched_stop
(here -
https://elixir.bootlin.com/linux/v5.11.1/source/drivers/gpu/drm/scheduler/sched_main.c#L385)
after sched thread is stopped and continue with the reset procedure.
Andrey
Hope above example helps
Thanks
*发件人:*Grodzovsky, Andrey <andrey.grodzov...@amd.com>
*发送时间:*2021年2月27日0:50
*收件人:*Liu, Monk <monk....@amd.com>; Koenig, Christian
<christian.koe...@amd.com>; amd-gfx@lists.freedesktop.org
*抄送:*Zhang, Andy <andy.zh...@amd.com>; Chen, Horace
<horace.c...@amd.com>; Zhang, Jack (Jian) <jack.zha...@amd.com>
*主题:*Re: [RFC] a new approach to detect which ring is the real black
sheep upon TDR reported
On 2021-02-26 6:54 a.m., Liu, Monk wrote:
[AMD Official Use Only - Internal Distribution Only]
See in line
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
*From:*Koenig, Christian <christian.koe...@amd.com>
<mailto:christian.koe...@amd.com>
*Sent:* Friday, February 26, 2021 3:58 PM
*To:* Liu, Monk <monk....@amd.com> <mailto:monk....@amd.com>;
amd-gfx@lists.freedesktop.org <mailto:amd-gfx@lists.freedesktop.org>
*Cc:* Zhang, Andy <andy.zh...@amd.com>
<mailto:andy.zh...@amd.com>; Chen, Horace <horace.c...@amd.com>
<mailto:horace.c...@amd.com>; Zhang, Jack (Jian)
<jack.zha...@amd.com> <mailto:jack.zha...@amd.com>
*Subject:* Re: [RFC] a new approach to detect which ring is the
real black sheep upon TDR reported
Hi Monk,
in general an interesting idea, but I see two major problems with
that:
1. It would make the reset take much longer.
2. Things get often stuck because of timing issues, so a guilty
job might pass perfectly when run a second time.
[ML] but the innocent ring already reported a TDR, and the drm
sched logic already deleted this “sched_job” in its mirror list,
thus you don’t have chance to re-submit it again after reset,
that’s the major problem here.
Just to confirm I understand correctly, Monk reports a scenario where
the second TDR that was reported by the innocent job is bailing out
BEFORE having a chance to run drm_sched_stop for that scheduler which
should have reinserted the job back into mirror list (because the
first TDR run is still in progress and hence amdgpu_device_lock_adev
fails for the second TDR) and so the innocent job which was extracted
from mirror list in drm_sched_job_timedout is now lost.
If so and as a possible quick fix until we overhaul the entire design
as suggested in this thread - maybe we can modify
drm_sched_backend_ops.timedout_job callback to report back premature
termination BEFORE drm_sched_stop had a chance to run and then
reinsert back the job into mirror list from within
drm_sched_job_timedout? There is no problem of racing against
concurrent drm_sched_get_cleanup_job once we reinsert there as we
don't reference the job pointer anymore after this point and so if
it's already signaled and freed right away - it's ok.
Andrey
Apart from that the whole ring mirror list turned out to be a
really bad idea. E.g. we still struggle with object life time
because the concept doesn't fit into the object model of the GPU
scheduler under Linux.
We should probably work on this separately and straighten up the
job destruction once more and keep the recovery information in the
fence instead.
[ML] we claim to our customer that no innocent process will be
dropped or cancelled, and our current logic works for the most
time, but only when there are different process running on
gfx/computes rings then we would run into the tricky situation I
stated here, and the proposal is the only way I can figure out so
far, do you have a better solution or idea we review it as another
candidate RFC ? Be note that we raised this proposal is because we
do hit our trouble and we do need to resolve it …. So even a not
perfect solution is still better than just cancel the innocent job
(and their context/process)
Thanks !
Regards,
Christian.
Am 26.02.21 um 06:58 schrieb Liu, Monk:
[AMD Public Use]
Hi all
NAVI2X project hit a really hard to solve issue now, and it
is turned out to be a general headache of our TDR mechanism ,
check below scenario:
1. There is a job1 running on compute1 ring at timestamp
2. There is a job2 running on gfx ring at timestamp
3. Job1 is the guilty one, and job1/job2 were scheduled to
their rings at almost the same timestamp
4. After 2 seconds we receive two TDR reporting from both GFX
ring and compute ring
5. *Current scheme is that in drm scheduler all the head jobs
of those two rings are considered “bad job” and taken away
from the mirror list *
6. The result is both the real guilty job (job1) and the
innocent job (job2) were all deleted from mirror list, and
their corresponding contexts were also treated as
guilty*(so the innocent process remains running is not
secured)*
**
But by our wish the ideal case is TDR mechanism can detect
which ring is the guilty ring and the innocent ring can
resubmits all its pending jobs:
1. Job1 to be deleted from compute1 ring’s mirror list
2. Job2 is kept and resubmitted later and its belonging
process/context are even not aware of this TDR at all
Here I have a proposal tend to achieve above goal and it rough
procedure is :
1. Once any ring reports a TDR, the head job is **not**
treated as “bad job”, and it is **not** deleted from the
mirror list in drm sched functions
2. In vendor’s function (our amdgpu driver here):
* reset GPU
* repeat below actions on each RINGS * one by one *:
1.take the head job and submit it on this ring
2.see if it completes, if not then this job is the real “bad job”
3. take it away from mirror list if this head job is “bad job”
* After above iteration on all RINGS, we already clears
all the bad job(s)
3. Resubmit all jobs from each mirror list to their
corresponding rings (this is the existed logic)
The idea of this is to use “serial” way to re-run and re-check
each head job of each RING, in order to take out the real
black sheep and its guilty context.
P.S.: we can use this approaches only on GFX/KCQ ring reports
TDR , since those rings are intermutually affected to each
other. For SDMA ring timeout it definitely proves the head job
on SDMA ring is really guilty.
Thanks
------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------
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