Re: [PATCH] sched/fair: Remove setting task's se->runnable_weight during PELT update

[Dietmar Eggemann]

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.