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

Liu, Monk Monk.Liu at amd.com
Fri Feb 26 11:54:01 UTC 2021

[AMD Official Use Only - Internal Distribution Only]

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Monk Liu | Cloud-GPU Core team

From: Koenig, Christian <Christian.Koenig at amd.com>
Sent: Friday, February 26, 2021 3:58 PM
To: Liu, Monk <Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org
Cc: Zhang, Andy <Andy.Zhang at amd.com>; Chen, Horace <Horace.Chen at amd.com>; Zhang, Jack (Jian) <Jack.Zhang1 at 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.

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 !

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)

  1.  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.


Monk Liu | Cloud-GPU Core team

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