回复: [RFC] a new approach to detect which ring is the real black sheep upon TDR reported

"Liu, Monk" <Monk.Liu@xxxxxxx> · Sat, 27 Feb 2021 03:50:33 +0000

[AMD Official Use Only - Internal Distribution Only]

the code I pasted is to illustrate why the innocent job is already taken out in the mirror list thus my suggested proposal won’t work unless we don’t delete the job in sched_job_timeout()
 routine, and the problem you stated is with my understanding also kind of related with my suggested solution – the job removing from list should be handled by driver instead of scheduler .

let make scheduler’s duty clear and simple : the sched_job_timeout() only get notification when a sched_job timedout but it doesn’t judge  if the leading job in mirror list should
 be blamed , all those checking should be left to driver to take action.

>> If we do this we should probably make it configurable as a module parameter.
That’s ok,  maybe we can reuse the existed parm “gpu_recovery”, extend it with:

l 
0 – no recovery initiated after job timeout

l 
1 – legacy TDR behave

l 
2 – enhanced TDR behave (the one suggested here)

发件人: Koenig, Christian <Christian.Koenig@xxxxxxx>

发送时间: 2021年2月26日 20:05

收件人: Liu, Monk <Monk.Liu@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx

抄送: Zhang, Andy <Andy.Zhang@xxxxxxx>; Chen, Horace <Horace.Chen@xxxxxxx>; Zhang, Jack (Jian) <Jack.Zhang1@xxxxxxx>

主题: Re: [RFC] a new approach to detect which ring is the real black sheep upon TDR reported

Yeah that is exactly the stuff which doesn't works at all. We got feedback for multiple people that this whole approach of tying the job to the tdr was not a good idea at all.

What we should do instead is to have a pointer in the scheduler fence to which job it belongs. Freeing up the job when the scheduler fence is signaled is then job of the driver and not the scheduler any more.

The scheduler then gives the scheduler fence to the driver when a timeout is detected and the driver can do the rest of the handling all by itself.

But this problem is orthogonal to the suggested solution here.

do you have a better solution or idea we review it as another candidate RFC ?

I don't see much other option either. We could do something like only allowing one application at a time to use the gfx/compute block, but that would be even worse.

If we do this we should probably make it configurable as a module parameter.

Regards,

Christian.

Am 26.02.21 um 12:57 schrieb Liu, Monk:

[AMD Official Use Only - Internal Distribution Only]

static void drm_sched_job_timedout(struct work_struct *work)
279 {
280     struct drm_gpu_scheduler *sched;
281     struct drm_sched_job *job;
282
283     sched = container_of(work, struct drm_gpu_scheduler, work_tdr.work);
284
285     /* Protects against concurrent deletion in drm_sched_get_cleanup_job */
286     spin_lock(&sched->job_list_lock);
287     job = list_first_entry_or_null(&sched->ring_mirror_list,
288                        struct drm_sched_job, node);
289
290     if (job) {
291         /*
292          * Remove the bad job so it cannot be freed by concurrent
293          * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
294          * is parked at which point it's safe.
295          */
296         list_del_init(&job->node);
297         spin_unlock(&sched->job_list_lock);
298
299         job->sched->ops->timedout_job(job);

Thanks 

------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------

From: Liu, Monk

Sent: Friday, February 26, 2021 7:54 PM

To: Koenig, Christian <Christian.Koenig@xxxxxxx>;
amd-gfx@xxxxxxxxxxxxxxxxxxxxx

Cc: Zhang, Andy <Andy.Zhang@xxxxxxx>; Chen, Horace
<Horace.Chen@xxxxxxx>; Zhang, Jack (Jian)
<Jack.Zhang1@xxxxxxx>

Subject: RE: [RFC] a new approach to detect which ring is the real black sheep upon TDR reported

[AMD Official Use Only - Internal Distribution Only]

See in line

Thanks 

------------------------------------------
Monk Liu | Cloud-GPU Core team
------------------------------------------

From: Koenig, Christian <Christian.Koenig@xxxxxxx>

Sent: Friday, February 26, 2021 3:58 PM

To: Liu, Monk <Monk.Liu@xxxxxxx>; 
amd-gfx@xxxxxxxxxxxxxxxxxxxxx

Cc: Zhang, Andy <Andy.Zhang@xxxxxxx>; Chen, Horace <Horace.Chen@xxxxxxx>; Zhang, Jack (Jian) <Jack.Zhang1@xxxxxxx>

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.

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:

There is a job1 running on compute1 ring at timestamp
There is a job2 running on gfx ring at timestamp
Job1 is the guilty one, and job1/job2 were scheduled to their rings at almost the same timestamp
After 2 seconds we receive two TDR reporting from both GFX ring and compute ring
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
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:

Job1 to be deleted from compute1 ring’s mirror list
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 :

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
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)

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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