Messages in this thread Patch in this message | | | Date | Fri, 26 Apr 2024 11:36:57 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue |
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On Fri, Apr 26, 2024 at 11:32:41AM +0200, Peter Zijlstra wrote: > On Thu, Apr 25, 2024 at 01:49:49PM +0200, Peter Zijlstra wrote: > > On Thu, Apr 25, 2024 at 12:42:20PM +0200, Peter Zijlstra wrote: > > > > > > I wonder if the delayed dequeue logic is having an unwanted effect on the calculation of > > > > utilization/load of the runqueue and, as a consequence, we're scheduling things to run on > > > > higher OPP's in the big cores, leading to poor decisions for energy efficiency. > > > > > > Notably util_est_update() gets delayed. Given we don't actually do an > > > enqueue when a delayed task gets woken, it didn't seem to make sense to > > > update that sooner. > > > > The PELT runnable values will be inflated because of delayed dequeue. > > cpu_util() uses those in the @boost case, and as such this can indeed > > affect things. > > > > This can also slightly affect the cgroup case, but since the delay goes > > away as contention goes away, and the cgroup case must already assume > > worst case overlap, this seems limited. > > > > /me goes ponder things moar. > > First order approximation of a fix would be something like the totally > untested below I suppose... > > --- > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index cfd1fd188d29..f3f70b5adca0 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5391,6 +5391,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > if (cfs_rq->next == se) > cfs_rq->next = NULL; > se->sched_delayed = 1; > + update_load_avg(cfs_rq, se, 0); > return false; > } > } > @@ -6817,6 +6818,7 @@ requeue_delayed_entity(struct sched_entity *se) > } > > se->sched_delayed = 0; > + update_load_avg(qcfs_rq, se, 0);
Compiler demands this ^^^^^ be cfs_rq instead ;-) brown_paper_bags--;
> } > > /* > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index d07a3b98f1fb..d16529613123 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -810,6 +810,9 @@ static inline void se_update_runnable(struct sched_entity *se) > > static inline long se_runnable(struct sched_entity *se) > { > + if (se->sched_delayed) > + return false; > + > if (entity_is_task(se)) > return !!se->on_rq; > else > @@ -823,6 +826,9 @@ static inline void se_update_runnable(struct sched_entity *se) {} > > static inline long se_runnable(struct sched_entity *se) > { > + if (se->sched_delayed) > + return false; > + > return !!se->on_rq; > } > #endif
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