On Sun, Sep 18, 2016 at 07:28:32AM +0800, Wanpeng Li wrote: > 2016-09-17 9:28 GMT+08:00 Joonwoo Park <[email protected]>: > > From: Srivatsa Vaddagiri <[email protected]> > > > > SCHED_HRTICK feature is useful to preempt SCHED_FAIR tasks on-the-dot > > (just when they would have exceeded their ideal_runtime). It makes use > > of a per-cpu hrtimer resource and hence alarming that hrtimer should > > be based on total SCHED_FAIR tasks a cpu has across its various cfs_rqs, > > rather than being based on number of tasks in a particular cfs_rq (as > > implemented currently). As a result, with current code, its possible for > > a running task (which is the sole task in its cfs_rq) to be preempted > > not be preempted much, right?
I don't think so.... By saying 'to be preempted much after its ideal_runtime has elapsed' I wanted to describe the current suboptimal behaviour. Thanks, Joonwoo > > > much after its ideal_runtime has elapsed, resulting in increased latency > > for tasks in other cfs_rq on same cpu. > > > > Fix this by alarming sched hrtimer based on total number of SCHED_FAIR > > tasks a CPU has across its various cfs_rqs. > > > > Cc: Ingo Molnar <[email protected]> > > Cc: Peter Zijlstra <[email protected]> > > Cc: [email protected] > > Signed-off-by: Srivatsa Vaddagiri <[email protected]> > > Signed-off-by: Joonwoo Park <[email protected]> > > --- > > > > joonwoop: Do we also need to update or remove if-statement inside > > hrtick_update()? > > I guess not because hrtick_update() doesn't want to start hrtick when > > cfs_rq > > has large number of nr_running where slice is longer than sched_latency. > > > > 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 4088eed..c55c566 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -4458,7 +4458,7 @@ static void hrtick_start_fair(struct rq *rq, struct > > task_struct *p) > > > > WARN_ON(task_rq(p) != rq); > > > > - if (cfs_rq->nr_running > 1) { > > + if (rq->cfs.h_nr_running > 1) { > > u64 slice = sched_slice(cfs_rq, se); > > u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime; > > s64 delta = slice - ran; > > -- > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > > hosted by The Linux Foundation > >
