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

[Koenig, Christian]

Am 18.01.19 um 18:34 schrieb 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.

Ok sounds good. We should probably discuss less on details and prototype 
a bit more.

Might be that I'm missing something here as well, so probably good to 
have some code to talk about things more directly.

Christian.

>
> 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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