Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 17 Jun 2016 14:00:43 +0200 | Subject | Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice when switching to fair or changing task group |
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On 17 June 2016 at 04:12, Yuyang Du <yuyang.du@intel.com> wrote: > > On Thu, Jun 16, 2016 at 11:21:55PM +0200, Vincent Guittot wrote: > > On 16 June 2016 at 22:07, Peter Zijlstra <peterz@infradead.org> wrote: > > > On Thu, Jun 16, 2016 at 09:00:57PM +0200, Vincent Guittot wrote: > > >> On 16 June 2016 at 20:51, Peter Zijlstra <peterz@infradead.org> wrote: > > >> > On Thu, Jun 16, 2016 at 06:30:13PM +0200, Vincent Guittot wrote: > > >> >> With patch [1] for the init of cfs_rq side, all use cases will be > > >> >> covered regarding the issue linked to a last_update_time set to 0 at > > >> >> init > > >> >> [1] https://lkml.org/lkml/2016/5/30/508 > > >> > > > >> > Aah, wait, now I get it :-) > > >> > > > >> > Still, we should put cfs_rq_clock_task(cfs_rq) in it, not 1. And since > > >> > we now acquire rq->lock on init this should well be possible. Lemme sort > > >> > that. > > >> > > >> yes with the rq->lock we can use cfs_rq_clock_task which is make more > > >> sense than 1. > > >> But the delta can be still significant between the creation of the > > >> task group and the 1st task that will be attach to the cfs_rq > > > > > > Ah, I think I've spotted more fail. > > > > > > And I think you're right, it doesn't matter, in fact, 0 should have been > > > fine too! > > > > > > enqueue_entity() > > > enqueue_entity_load_avg() > > > update_cfs_rq_load_avg() > > > now = clock() > > > __update_load_avg(&cfs_rq->avg) > > > cfs_rq->avg.last_load_update = now > > > // ages 0 load/util for: now - 0 > > > if (migrated) > > > attach_entity_load_avg() > > > se->avg.last_load_update = cfs_rq->avg.last_load_update; // now != 0 > > > > > > So I don't see how it can end up being attached again. > > > > In fact it has already been attached during the sched_move_task. The > > sequence for the 1st task that is attached to a cfs_rq is : > > > > sched_move_task() > > task_move_group_fair() > > detach_task_cfs_rq() > > set_task_rq() > > attach_task_cfs_rq() > > attach_entity_load_avg() > > se->avg.last_load_update = cfs_rq->avg.last_load_update == 0 > > > > Then again, does this fix it?
Peter's proposal to update the cfs_rq before attaching/detaching the task, fixes the problem
> > > static void task_move_group_fair(struct task_struct *p) > { > detach_task_cfs_rq(p); > set_task_rq(p, task_cpu(p)); > attach_task_cfs_rq(p); > /* > * If the cfs_rq's last_update_time is 0, attach the sched avgs > * won't be anything useful, as it will be decayed to 0 when any > * sched_entity is enqueued to that cfs_rq. > * > * On the other hand, if the cfs_rq's last_update_time is 0, we > * must reset the task's last_update_time to ensure we will attach > * the sched avgs when the task is enqueued. > */ > if (!cfs_rq_of(&p->se)->avg.last_update_time) > reset_task_last_update_time(p); > else > attach_entity_load_avg(cfs_rq_of(&p->se), &p->se); > }
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