On 01/08/2020 04:32, Jiang Biao wrote: > From: Jiang Biao <benbji...@tencent.com> > > No need to preempt when there are only one runable CFS task with > other IDLE tasks on runqueue. The only one CFS task would always > be picked in that case. > > Signed-off-by: Jiang Biao <benbji...@tencent.com> > --- > kernel/sched/fair.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 04fa8dbcfa4d..8fb80636b010 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4527,7 +4527,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity > *curr, int queued) > return; > #endif > > - if (cfs_rq->nr_running > 1) > + if (cfs_rq->nr_running > cfs_rq.idle_h_nr_running + 1)
cfs_rq is a pointer. > check_preempt_tick(cfs_rq, curr); > } You can't compare cfs_rq->nr_running with cfs_rq->idle_h_nr_running! There is a difference between cfs_rq->h_nr_running and cfs_rq->nr_running. The '_h_' stands for hierarchical. The former gives you hierarchical task accounting whereas the latter is the number of sched entities (representing tasks or taskgroups) enqueued in cfs_rq. In entity_tick(), cfs_rq->nr_running has to be used for the condition to call check_preempt_tick(). We want to check if curr has to be preempted by __pick_first_entity(cfs_rq) on this cfs_rq. entity_tick() is called for each sched entity (and so for each cfs_rq_of(se)) of the task group hierarchy (e.g. task p running in taskgroup /A/B : se(p) -> se(A/B) -> se(A)).
