On Mon, Apr 18, 2016 at 10:00:42AM +0800, Wanpeng Li wrote: > > H is for hierarchy. That counts the total of runnable tasks in the > > entire child hierarchy. Nr_running is the number of se entities in > > the current tree. > > So I think we should at least change cfs_rq->nr_running to > cfs->h_nr_running, I can send a formal patch if you think it makes > sense. :-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1159423..79197df 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -616,7 +616,7 @@ bool sched_can_stop_tick(struct rq *rq) > } > > /* Normal multitasking need periodic preemption checks */ > - if (rq->cfs.nr_running > 1) > + if (rq->cfs.h_nr_running > 1) > return false; > > return true;
So I think that is indeed the right thing here. But looking at this function I think there's more problems with it. It seems to assume that if there's FIFO tasks, those will run. This is incorrect. The FIFO task can have a lower prio than an RR task, in which case the RR task will run. So the whole fifo_nr_running test seems misplaced, it should go after the rr_nr_running tests. That is, only if !rr_nr_running, can we use fifo_nr_running like this.
