2016-09-17 9:28 GMT+08:00 Joonwoo Park <joonw...@codeaurora.org>: > From: Srivatsa Vaddagiri <va...@codeaurora.org> > > 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? > 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 <mi...@redhat.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Srivatsa Vaddagiri <va...@codeaurora.org> > Signed-off-by: Joonwoo Park <joonw...@codeaurora.org> > --- > > 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 >