[PATCH v5 1/2] drm/sched: Refactor ring mirror list handling.

[Grodzovsky, Andrey]

On 01/18/2019 04:25 AM, Koenig, Christian wrote:
> [SNIP]
>>>>> Re-arming the timeout should probably have a much reduced value
>>>>> when the job hasn't changed. E.g. something like a few ms.
>> Now i got thinking about non hanged job in progress (job A) and let's
>> say it's a long job , it just started executing but due to time out of
>> another job (job B) on another (or this scheduler) it's parent cb got
>> disconnected, we disarmed the tdr timer for the job's scheduler,
>> meanwhile the timed out job did manage to complete before HW reset
>> check and hence we skip HW reset, attach back the cb and rearm job's A
>> tdr  timer with a future value of few ms only - aren't we going to get
>> false tdr triggered on job B now because we didn't let it enough time
>> to run and complete ? I would prefer the other extreme of longer time
>> for time out to trigger then false TDR. Optimally we would have per
>> job timer and rearm to exactly the reminder of it's time out value -
>> but we gave up on per job tdr work long ago.
> Well we only re-arm the timeout with a shorter period if it already
> triggered once. If we just suspend the timeout then we should still use
> the longer period.

Can you explain more on this ? I don't get it.

Andrey

>
>> In general the more i think about it  (correct me if I am wrong) I am
>> less sure how much the optimization feature is useful - if job's time
>> out did trigger what are the chances that the little more time we give
>> it between beginning of tdr function and the time we do start the
>> actual HW reset will be exactly what it needed to complete. Also, this
>> is still not water proof as the job might complete and signal it's HW
>> fence exactly after we checked for completion but before starting the
>> HW reset code.
> I don't see this as an optimization, but rather as mandatory for correct
> operation.
>
> See without this we can run into issues because we execute jobs multiple
> times. That can still happen with this clean handling, but it is much
> more unlikely.
>
> Christian.
>
>> Andrey
>>
>>>> By unchanged you mean when we didn't resubmit the job because of the
>>>> optimized non HW reset, right ?
>>> Correct, yes.
>>>
>>>>>> About flushing tdr jobs in progress from .free_job cb - looks like
>>>>>> drm_sched_job_finish->cancel_delayed_work_sync is not enough, we
>>>>>> still need to take care of flushing all sced->work_tdr for a
>>>>>> device and for all devices in hive for XGMI.
>>>>>> What do you think ?
>>>>> Why should that be necessary? We only wait for the delayed work to
>>>>> make sure that the job is not destroyed while dealing with it.
>>>>>
>>>>> Christian.
>>>> But we might not be waiting for the correct sched->work_tdr, we do
>>>> the reset routine for all schedulers in a device accessing their
>>>> jobs too and not only for the scheduler to which the job belongs.
>>>> For XGMI not only that, we reset all the devices in the hive.
>>> That is harmless you only need to wait for the work_tdr of the
>>> current scheduler, not for all of them.
>>>
>>>> I was thinking, amdgpu driver is not even interested in allowing
>>>> multiple sced->tdr to execute together - we have to serialize all of
>>>> them anyway with the trylock mutex (even without XGMI), v3d in
>>>> v3d_job_timedout seems also to reset all of his schedulers from the
>>>> tdr work. Would it make sense to provide the sched->work_td as init
>>>> parameter to scheduler (same one for all schedulers) so we can
>>>> enforce serialization by disallowing more then 1 tdr work to execute
>>>> in the same time ? Other drivers interested to do in parallel can
>>>> provide unique sched->work_tdr per scheduler. This does  imply
>>>> drm_sched_job_timedout has to removed and delegated to specific
>>>> driver implementation as probably other code dealing with
>>>> sched->work_tdr... Maybe even move tdr handling to the driver all
>>>> together ?
>>> Yeah, I was thinking something similar. The problem with this
>>> approach is that a delayed work item can have only one delay, but for
>>> multiple engines we need multiple delays.
>>>
>>> What we could do is to make it a timer instead and raise the work
>>> item from the device specific callback.
>>>
>>> But that doesn't really saves us the stop all schedulers trouble, so
>>> it doesn't buy us much in the end if I see this correctly.
>>>
>>> Christian.
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