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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 > > >> > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to majordomo@...r.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@...r.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@...r.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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