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SubjectRe: [PATCH] sched/fair: Remove setting task's se->runnable_weight during PELT update
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On 07/11/2018 01:09 AM, Joel Fernandes wrote:
> On Mon, Jul 09, 2018 at 05:47:53PM +0100, Dietmar Eggemann wrote:
>> A CFS (SCHED_OTHER, SCHED_BATCH or SCHED_IDLE policy) task's
>> se->runnable_weight must always be in sync with its se->load.weight.
>>
>> se->runnable_weight is set to se->load.weight when the task is
>> forked (init_entity_runnable_average()) or reniced (reweight_entity()).
>>
>> There are two cases in set_load_weight() which since they currently only
>> set se->load.weight could lead to a situation in which se->load.weight
>> is different to se->runnable_weight for a CFS task:
>>
>> (1) A task switches to SCHED_IDLE.
>>
>> (2) A SCHED_FIFO, SCHED_RR or SCHED_DEADLINE task which has been reniced
>> (during which only its static priority gets set) switches to
>> SCHED_OTHER or SCHED_BATCH.
>>
>> Set se->runnable_weight to se->load.weight in these two cases to prevent
>> this. This eliminates the need to explicitly set it to se->load.weight
>> during PELT updates in the CFS scheduler fastpath.
>
> Looks good to me. By the way just asking, is there a chance where
> se_weight(se) and se_runnable(se) can ever be different?

Yes they can be different, not for a task though but for se's
representing task groups. It got introduced to be able to propagate load
and runnable load independently through the task groups hierarchies.

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