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SubjectRe: [PATCH v4 08/10] sched/fair: Steal work from an overloaded CPU when CPU goes idle
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On 12/7/2018 3:21 PM, Valentin Schneider wrote:
> Hi Steve,
>
> On 06/12/2018 21:28, Steve Sistare wrote:
> [...]
>> @@ -6778,20 +6791,22 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
>> update_misfit_status(NULL, rq);
>>
>> /*
>> - * We must set idle_stamp _before_ calling idle_balance(), such that we
>> - * measure the duration of idle_balance() as idle time.
>> + * We must set idle_stamp _before_ calling try_steal() or
>> + * idle_balance(), such that we measure the duration as idle time.
>> */
>> rq_idle_stamp_update(rq);
>
> idle_balance() has a
>
> /*
> * Do not pull tasks towards !active CPUs...
> */
> if (!cpu_active(this_cpu))
> return 0;
>
> check which we probably want for stealing too, so we could hoist it up here
> to cover both idle_balance() and try_steal().

try_steal() already checks cpu_active. I could hoist it.

- Steve

>
>> new_tasks = idle_balance(rq, rf);
>> + if (new_tasks == 0)
>> + new_tasks = try_steal(rq, rf);
>>
>> if (new_tasks)
>> rq_idle_stamp_clear(rq);
>>
>> /*
>> - * Because idle_balance() releases (and re-acquires) rq->lock, it is
>> - * possible for any higher priority task to appear. In that case we
>> - * must re-start the pick_next_entity() loop.
>> + * Because try_steal() and idle_balance() release (and re-acquire)
>> + * rq->lock, it is possible for any higher priority task to appear.
>> + * In that case we must re-start the pick_next_entity() loop.
>> */
>> if (new_tasks < 0)
>> return RETRY_TASK;
> [...]
>

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