On 2/11/20 10:55 AM, Andrey Grodzovsky wrote:
On 2/10/20 4:50 PM, Luben Tuikov wrote:
Hi Lucas,
Thank you for bringing awareness of this issue, publicly.
As soon as this patch showed up back in November of 2019,
I objected to it, privately.
I didn't find this objection in my mail actually
I suggested to instead use a _list_ to store the "state" of
all jobs of the same state. Then, at any time, timeout interrupt
or whatever, we can atomically (irq spinlock) move the timeout/bad
job to the timedout/cleanup/bad job list, and wake someone up
to deal with that list asynchronously, and return from the
interrupt/etc.
immediately.
Sounds a good idea to me, i think enough for us to have 2 lists,
timeout list for jobs scheduled to HW and not yet completed
(completion fence signaled) and cleanup list for those that did
complete. This should give alternative solution to the race condition
this patch was addressing without causing the break the Lucas
reported. If no one objects I think i can try implement it.
Andrey
Thinking more i realize Luben is right about having also bad job list as
this is needed for normal job competition (by fence callback from
amdgpu_fence_process) and you need to decide if you move it to cleanup
list from timeout list or not. If it's already in bad job list - meaning
that it's being processed by GPU recovery code you don't touch it,
otherwise you move it to cleanup list where it will be freed eventually
by invocation of drm_sched_get_cleanup_job.
Andrey
Then in due time, if any more interrupts or whatnot take place,
the job will either be in the timeout list or not. If it it,
then the instigator backs off as someone else (the list handler) will/is
awake and handling it (obviously a state variable may be kept as well).
This draws somewhat from my days with iSCSI, SCSI and SAS, 15 years ago,
where a device can complete a job (task) at anytime regardless
of what the SCSI layer "thinks" the task's state is: timed-out, aborted,
whatever. It is a very simple and elegant solution which generalizes
well.
Regards,
Luben
On 2020-02-10 11:55 a.m., Andrey Grodzovsky wrote:
Lucas - Ping on my question and also I attached this temporary
solution for etnaviv to clarify my point. If that something
acceptable for now at least i can do the same for v3d where it
requires a bit more code changes.
Andrey
On 2/6/20 10:49 AM, Andrey Grodzovsky wrote:
Well a revert would break our driver.
The real solution is that somebody needs to sit down, gather ALL
the requirements and then come up with a solution which is clean
and works for everyone.
Christian.
I can to take on this as indeed our general design on this becomes
more and more entangled as GPU reset scenarios grow in complexity
(at least in AMD driver). Currently I am on a high priority
internal task which should take me around a week or 2 to finish and
after that I can get to it.
Regarding temporary solution - I looked into v3d and etnaviv use
cases and we in AMD actually face the same scenario where we decide
to skip HW reset if the guilty job did finish by the time we are
processing the timeout (see amdgpu_device_gpu_recover and
skip_hw_reset goto) - the difference is we always call
drm_sched_stop/start irrespectively of whether we are going to
actually HW reset or not (same as extend timeout). I wonder if
something like this can be done also for ve3 and etnaviv ?
Andrey
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