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

[Grodzovsky, Andrey]

On 01/18/2019 12:10 PM, Koenig, Christian wrote:
> Am 18.01.19 um 16:21 schrieb 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.
> See drm_sched_job_timedout(), we re-arm the timeout at the end of the
> procedure.
>
> We should change that and re-arm the timer with a much lower timeout if
> the job is still not finished.
>
> Christian.

I still don't see how this can fix the problem of of long job in 
progress triggering false tdr if no HW reset was done, but maybe I am 
missing other pieces you have in mind, I will finish the patch and send 
it and then we can be more specific based on the code.

Andrey

>
>> 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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