Messages in this thread | | | Date | Tue, 8 Sep 2015 15:32:40 +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 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?
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.
> > 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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