Messages in this thread | | | Date | Mon, 19 Jan 2015 13:45:28 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 5/7] sched/fair: fix idle balance when remaining tasks are all non-CFS tasks |
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On Wed, Nov 26, 2014 at 08:44:05AM +0800, Wanpeng Li wrote: > The overload indicator is used for knowing when we can totally avoid load > balancing to a cpu that is about to go idle. We can avoid load balancing > when no cpu has cfs task and both rt and deadline have push/pull mechanism > to do their own balancing. > > However, rq->nr_running on behalf of the total number of each class tasks > on the cpu, do idle balance when remaining tasks are all non-CFS tasks does > not make any sense. > > This patch fix it by idle balance when there are still other CFS tasks in > the rq's root domain. >
Please always try and Cc the people who touched that code last; for the idle_balance bits commit 4486edd12b5a ("sched/fair: Implement fast idling of CPUs when the system is partially loaded") gives a fair clue as to who that would be.
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 31f1e4d..f7dd978 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1269,7 +1269,8 @@ static inline void add_nr_running(struct rq *rq, unsigned count) > > rq->nr_running = prev_nr + count; > > - if (prev_nr < 2 && rq->nr_running >= 2) { > + if (prev_nr < 2 && rq->nr_running >= 2 && > + rq->cfs.h_nr_running > 0) { > #ifdef CONFIG_SMP > if (!rq->rd->overload) > rq->rd->overload = true;
Here 3882ec643997 ("nohz: Use IPI implicit full barrier against rq->nr_running r/w") might be a clue.
Also, this is wrong, it breaks NOHZ_FULL.
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