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SubjectRe: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process.
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Am 30.04.2018 um 16:32 schrieb Andrey Grodzovsky:
>
>
> On 04/30/2018 08:08 AM, Christian König wrote:
>> Hi Eric,
>>
>> sorry for the late response, was on vacation last week.
>>
>> Am 26.04.2018 um 02:01 schrieb Eric W. Biederman:
>>> Andrey Grodzovsky <Andrey.Grodzovsky@amd.com> writes:
>>>
>>>> On 04/25/2018 01:17 PM, Oleg Nesterov wrote:
>>>>> On 04/25, Andrey Grodzovsky wrote:
>>>>>> here (drm_sched_entity_fini) is also a bad idea, but we still
>>>>>> want to be
>>>>>> able to exit immediately
>>>>>> and not wait for GPU jobs completion when the reason for reaching
>>>>>> this code
>>>>>> is because of KILL
>>>>>> signal to the user process who opened the device file.
>>>>> Can you hook f_op->flush method?
>>
>> THANKS! That sounds like a really good idea to me and we haven't
>> investigated into that direction yet.
>>
>>>> But this one is called for each task releasing a reference to the
>>>> the file, so
>>>> not sure I see how this solves the problem.
>>> The big question is why do you need to wait during the final closing a
>>> file?
>>
>> As always it's because of historical reasons. Initially user space
>> pushed commands directly to a hardware queue and when a processes
>> finished we didn't need to wait for anything.
>>
>> Then the GPU scheduler was introduced which delayed pushing the jobs
>> to the hardware queue to a later point in time.
>>
>> This wait was then added to maintain backward compability and not
>> break userspace (but see below).
>>
>>> The wait can be terminated so the wait does not appear to be simply a
>>> matter of correctness.
>>
>> Well when the process is killed we don't care about correctness any
>> more, we just want to get rid of it as quickly as possible (OOM
>> situation etc...).
>>
>> But it is perfectly possible that a process submits some render
>> commands and then calls exit() or terminates because of a SIGTERM,
>> SIGINT etc.. In this case we need to wait here to make sure that all
>> rendering is pushed to the hardware because the scheduler might need
>> resources/settings from the file descriptor.
>>
>> For example if you just remove that wait you could close firefox and
>> get garbage on the screen for a millisecond because the remaining
>> rendering commands where not executed.
>>
>> So what we essentially need is to distinct between a SIGKILL (which
>> means stop processing as soon as possible) and any other reason
>> because then we don't want to annoy the user with garbage on the
>> screen (even if it's just for a few milliseconds).
>>
>> Constructive ideas how to handle this would be very welcome, cause I
>> completely agree that what we have at the moment by checking
>> PF_SIGNAL is just a very very hacky workaround.
>
> What about changing PF_SIGNALED to  PF_EXITING in
> drm_sched_entity_do_release
>
> -       if ((current->flags & PF_SIGNALED) && current->exit_code ==
> SIGKILL)
> +      if ((current->flags & PF_EXITING) && current->exit_code ==
> SIGKILL)
>
> From looking into do_exit and it's callers , current->exit_code will
> get assign the signal which was delivered to the task. If SIGINT was
> sent then it's SIGINT, if SIGKILL then SIGKILL.

That's at least a band aid to stop us from abusing PF_SIGNALED.

But additional to that change, can you investigate when f_ops->flush()
is called when the process exists normally, because of SIGKILL or
because of some other signal?

Could be that this is more closely to what we are searching for,
Christian.

>
> Andrey
>
>
>>
>> Thanks,
>> Christian.
>
>
>>
>>>
>>> Eric
>>> _______________________________________________
>>> amd-gfx mailing list
>>> amd-gfx@lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>>
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

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