Messages in this thread | | | Date | Tue, 8 Sep 2015 11:10:30 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() |
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hello wanpeng,
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.
it is nothing to do with normalization.
if vruntime - cfs_rq->min_vruntime is big even though place_entity() was called when moved from fair class, then we actually expect that it still has a big vruntime when moved back to fair class.
if we don't expect that it still has a big vruntime when moved back to fair class, we need to consider other approaches e.g. to move a position calling place_entity() or to add place_entity() call properly ..
however we should not touch normalization logic. in other words, if we normalized the vruntime when leaved, then we should necessarily restore the vruntime to a non-normalized value when moved back.
> > 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.
could you explain this in detail? when is a vruntime not normalized?
thanks, byungchul
> > 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/
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