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Message-ID: <20150908064317.GG6455@byungchulpark-X58A-UD3R>
Date: Tue, 8 Sep 2015 15:43:17 +0900
From: Byungchul Park <byungchul.park@....com>
To: Wanpeng Li <wanpeng.li@...mail.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
yuyang.du@...el.com
Subject: Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair()
On Tue, Sep 08, 2015 at 02:28:17PM +0900, 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
> 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
i mean enqueue_entity(.flags=0), just when moved back.
> 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.
>
> > 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@...mail.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
> > >>
> >
> > --
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