Re: [PATCH 19/19] drm/i915: Sync against the GuC log buffer flush work item on system suspend

["Goel, Akash" <akash.goel@intel.com>]

On 8/18/2016 7:48 PM, Imre Deak wrote:
> On to, 2016-08-18 at 19:17 +0530, Goel, Akash wrote:
>> [...]
>> Thanks for the inputs. Sorry not familiar with freezable WQ semantics.
>> But after looking at code, this is what I understood :-
>> 1. freezable Workqueues will be frozen before the system suspend
>>     callbacks are invoked for the devices.
>
> Yes.
>
>> 2. Any work item queued after the WQ is marked frozen will be scheduled
>>     later, on resume.
>
> Yes.
>
>> 3. But if a work item was already present in the freezable Workqueue,
>>     before it was frozen and it did not complete, then system suspend
>>     itself will be aborted.
>
> System suspend will be aborted only if any kernel thread didn't
> complete within a reasonable amount of time (freeze_timeout_msecs, 20
> sec by default). Otherwise already queued items will be properly
> waited upon and suspend will proceed.
Sorry for getting this wrong.
What I understood is that even if there are pending work items on
freezable WQ after freeze_timeout_msecs, then also system suspend would 
be performed.
Sorry couldn't find an explicit/synchronous wait in kernel for the 
pending work items for freezable WQs, but it doesn't matter.

>
>> 4. So if the log.flush_wq is marked as freezable, then flush of
>>     work item will not be required for the system suspend case.
>>     And runtime suspend case is already covered with rpm get/put
>>     around register access in work item function.
>
> Yes.
>
>>
>> It seems there are 2 config options CONFIG_SUSPEND_FREEZER
>
> This is set whenever system suspend is enabled.
>
>> and
>> CONFIG_FREEZER
>
> This is set except for one platform (powerpc), where I assume freezing
> of the tasks is achieved in a different way. In any case it doesn't
> matter for us.
>
Many thanks for providing all this info.

Will then mark the log.flush_wq as freezable.

Best regards
Akash
> --Imre
>
>> which have to be enabled for all the above to happen.
>> If these config options will always be enabled then probably marking
>> log.flush_wq would work.
>>
>> Please kindly confirm whether I understood correctly or not, accordingly
>> will proceed further.
>>
>> Best regards
>> Akash
>>
>>
>>
>>> --Imre
>>>
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