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

Thu Jan 24 15:29:53 UTC 2019

OK, I will update patches 1 and 2 and given your RBs push them since 
they fix some races. I will then update and test patch 3 on some basic 
scenarios and will send it for separate review where I might put a TODO 
comment in code with my objections regarding long jobs form our 
discussion so you can see and reply on that.

Andrey

On 01/24/2019 06:34 AM, Koenig, Christian wrote:
> I see a few cleanups on Patch #3 which actually belong in patch #1:
>
>> +void drm_sched_stop(struct drm_gpu_scheduler *sched, struct
>> drm_sched_job *bad)
> The "bad" job parameter actually isn't used any more, isn't it?
>
>> +retry_wait:
> Not used any more.
>
> But apart from that at least patch #1 and #2 look like they can have my
> rb now.
>
> Patch #3 looks also like it should work after a bit of polishing.
>
> Thanks,
> Christian.
>
> Am 18.01.19 um 20:15 schrieb Grodzovsky, Andrey:
>> Attached series is the first 2 patches we already discussed about ring
>> mirror list handling racing with all your comments fixed (still not
>> committed). The third patch is a prototype based on the first 2 patches
>> and on our discussion.
>>
>> Please take a look.
>>
>> Andrey
>>
>>
>> On 01/18/2019 01:32 PM, Koenig, Christian wrote:
>>> 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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>>>>>>> amd-gfx at lists.freedesktop.org
>>>>>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx