Messages in this thread | | | Subject | Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() | From | Wanpeng Li <> | Date | Tue, 8 Sep 2015 14:42:52 +0800 |
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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, 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, 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/
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