Messages in this thread | | | Date | Tue, 8 Sep 2015 16:11:39 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() |
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On Tue, Sep 08, 2015 at 02:42:52PM +0800, Wanpeng Li wrote: > On 9/8/15 2:32 PM, Byungchul Park wrote: > >On Tue, Sep 08, 2015 at 03:14:26PM +0900, Byungchul Park wrote: > >>On Tue, Sep 08, 2015 at 01:38:08PM +0800, Wanpeng Li wrote: > >>>On 9/8/15 1:28 PM, Byungchul Park wrote: > >>>>On Tue, Sep 08, 2015 at 11:46:01AM +0800, Wanpeng Li wrote: > >>>>>On 9/7/15 10:02 PM, Peter Zijlstra wrote: > >>>>>>Please always Cc at least the person who wrote the lines you modify. > >>>>>> > >>>>>>On Mon, Sep 07, 2015 at 05:45:20PM +0800, Wanpeng Li wrote: > >>>>>>>The sleeper task will be normalized when moved from fair_sched_class, in > >>>>>>>order that vruntime will be adjusted either the task is running or sleeping > >>>>>>>when moved back. The nomalization in switch_to_fair for sleep task will > >>>>>>>result in lose fair sleeper bonus in place_entity() once the vruntime - > >>>>>>>cfs_rq->min_vruntime is big when moved from fair_sched_class. > >>>>>>> > >>>>>>>This patch fix it by adjusting vruntime just during migrating as original > >>>>>>>codes since the vruntime of the task has usually NOT been normalized in > >>>>>>>this case. > >>>>>>Sorry, I cannot follow that at all. Maybe its me being sleep deprived, > >>>>>>but could you try that again? > >>>>>When changing away from the fair class while sleeping, relative > >>>>>vruntime is calculated to handle the case sleep when moved from > >>>>>fair_sched_class and running when moved to fair_sched_class. The > >>>>i don't think relative vruntime is calculated to handle the special case > >>>>you mentioned. i think the calculation is necessary for all cases detaching > >>>Please refer why the relative vruntime caculation is introduced to > >>>switched_from_fair(): https://lkml.org/lkml/2011/1/17/129 > >>hello, > >> > >>it is just a bug caused by not calculating a relative vruntime when > >>detached a task from cfs_rq, which is necessary though. > >> > >>>>a task from a cfs_rq. > >>>> > >>>>>absolute vruntime will be calculated in enqueue_entity() either the > >>>>>task is running or sleeping when moved back. The fair sleeper bonus > >>>>i think absolute vruntime is calculated in enqueue_entuty() only when the > >>>>task is on rq. therefore in the case that the task is not on rq, > >>>>switched_to_fair() has to calculate the absolute vruntime instread. > >>>Absolute vruntime is caculated in place_entity() which is called by > >>>enqueue_entity() for DEQUEUE_SLEEP task. > >>as you may know, place_entity() is not for calculating an absolute > >>vruntime though.. anyway the important thing here is that, when a > >>sleeping task is moved back to fair class, enqueue_entity() for > >>DEQUEUE_SLEEP task won't be called. > >you may talk about calling enqueue_entity() when the task is woken up, > >not just when it is moved back. right? > > Exactly. > > > > >even if yes, i think place_entity() should not be used directly for > >calculating an absolute vruntime. it should be called after non/normalizing > >operations. > > The se->vruntime += cfs_rq->min_vruntime(in your switched_to_fair()) > which means that se->vruntime is bigger than cfs_rq->min_vruntime,
it is not always true since se->vruntime can have a negative value (even though it is a unsigned type.. i think it can be another problem) by se->vruntime -= cfs_rq->min_vruntime in detach_task_cfs_rq().
> however, fair sleeper bonus is min_vuntime - sysctl_sched_latency/2, > which means that max_vruntime() will select the absolute vruntime > which is caculated in your switched_to_fair() as the se->vruntime,
since se->vruntime can have a negative value, max_vruntime() may select the fair sleeper bonused value.
by the way, this logic is unchanged by my patch. which part of my patch changed this kind of logic?
thanks, byungchul
> then the fair sleeper bonus is lost in this case. > > Regards, > Wanpeng Li > > > > >>thanks, > >>byungchul > >> > >>>Regards, > >>>Wanpeng Li > >>> > >>>>>should be gained in place_entity() if the task is still sleeping. > >>>>>However, after recent commit ( 23ec30ddd7c1306: 'sched: add two > >>>>>functions for att(det)aching a task to(from) a cfs_rq'), the > >>>>>absolute vruntime will be calculated in switched_to_fair(), so the > >>>>>max_vruntime() which is called in place_entity() will select the > >>>>>absolute vruntime which is calculated in switched_to_fair() as the > >>>>>se->vruntime and lose the fair sleeper bonus. > >>>>please refer my another reply, and let me know if i missed something. > >>>> > >>>>thanks, > >>>>byungchul > >>>> > >>>>>Regards, > >>>>>Wanpeng Li > >>>>> > >>>>>>>Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> > >>>>>>>--- > >>>>>>> kernel/sched/fair.c | 11 +++++++---- > >>>>>>> 1 files changed, 7 insertions(+), 4 deletions(-) > >>>>>>> > >>>>>>>diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >>>>>>>index d26d3b7..eb9aa35 100644 > >>>>>>>--- a/kernel/sched/fair.c > >>>>>>>+++ b/kernel/sched/fair.c > >>>>>>>@@ -8005,9 +8005,6 @@ static void attach_task_cfs_rq(struct task_struct *p) > >>>>>>> /* Synchronize task with its cfs_rq */ > >>>>>>> attach_entity_load_avg(cfs_rq, se); > >>>>>>>- > >>>>>>>- if (!vruntime_normalized(p)) > >>>>>>>- se->vruntime += cfs_rq->min_vruntime; > >>>>>>> } > >>>>>>> static void switched_from_fair(struct rq *rq, struct task_struct *p) > >>>>>>>@@ -8066,14 +8063,20 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) > >>>>>>> #ifdef CONFIG_FAIR_GROUP_SCHED > >>>>>>> static void task_move_group_fair(struct task_struct *p) > >>>>>>> { > >>>>>>>+ struct sched_entity *se = &p->se; > >>>>>>>+ struct cfs_rq *cfs_rq = cfs_rq_of(se); > >>>>>>>+ > >>>>>>> detach_task_cfs_rq(p); > >>>>>>> set_task_rq(p, task_cpu(p)); > >>>>>>> #ifdef CONFIG_SMP > >>>>>>> /* Tell se's cfs_rq has been changed -- migrated */ > >>>>>>>- p->se.avg.last_update_time = 0; > >>>>>>>+ se->avg.last_update_time = 0; > >>>>>>> #endif > >>>>>>> attach_task_cfs_rq(p); > >>>>>>>+ > >>>>>>>+ if (!vruntime_normalized(p)) > >>>>>>>+ se->vruntime += cfs_rq->min_vruntime; > >>>>>>> } > >>>>>>> void free_fair_sched_group(struct task_group *tg) > >>>>>>>-- > >>>>>>>1.7.1 > >>>>>>> > >>>>>-- > >>>>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > >>>>>the body of a message to majordomo@vger.kernel.org > >>>>>More majordomo info at http://vger.kernel.org/majordomo-info.html > >>>>>Please read the FAQ at http://www.tux.org/lkml/ > >>>-- > >>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > >>>the body of a message to majordomo@vger.kernel.org > >>>More majordomo info at http://vger.kernel.org/majordomo-info.html > >>>Please read the FAQ at http://www.tux.org/lkml/ > >>-- > >>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > >>the body of a message to majordomo@vger.kernel.org > >>More majordomo info at http://vger.kernel.org/majordomo-info.html > >>Please read the FAQ at http://www.tux.org/lkml/ > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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