On Thu, Jul 16, 2015 at 10:00:00AM -0700, [email protected] wrote: hello,
> [email protected] writes: > > > From: Byungchul Park <[email protected]> > > > > hello paul, > > > > can i ask you something? > > > > when a sched entity is both waken and migrated, it looks being decayed > > twice. > > did you do it on purpose? > > or am i missing something? :( > > > > thanks, > > byungchul > > __synchronize_entity_decay() updates only se->avg.load_avg_contrib so > that removing from blocked_load is done correctly. as you said, it should done here. :) > update_entity_load_avg() accounts that (approximation of) time blocked i mean the entity was already accounted the blocked time in __synchronize_entity_decay(). > against runnable_avg/running_avg (and then recomputes load_avg_contrib > to match while load_avg_contrib isn't part of any cfs_rq's sum). the thing to keep in mind is that, currently load tracking is done by per-entity. that is, the entity already has its own whole load_avg_contrib with considering the entity's blocked time, after __synchronize_entity_decay(). and cfs_rq can account the se's load by adding se->avg.load_avg_contrib to cfs_rq->runnable_load_avg, like enqueue_entity_load_avg() code. wrong? thanks, byungchul > > > > > --------------->8--------------- > > From 793c963d0b29977a0f6f9330291a9ea469cc54f0 Mon Sep 17 00:00:00 2001 > > From: Byungchul Park <[email protected]> > > Date: Thu, 16 Jul 2015 16:49:48 +0900 > > Subject: [PATCH] sched: prevent sched entity from being decayed twice when > > both waking and migrating it > > > > current code is decaying load average variables with a sleep time twice, > > when both waking and migrating it. the first decaying happens in a call path > > "migrate_task_rq_fair() -> __synchronize_entity_decay()". the second > > decaying happens in a call path "enqueue_entity_load_avg() -> > > update_entity_load_avg()". so make it happen once. > > > > Signed-off-by: Byungchul Park <[email protected]> > > --- > > kernel/sched/fair.c | 29 +++-------------------------- > > 1 file changed, 3 insertions(+), 26 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 09456fc..c86cca0 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -2873,32 +2873,9 @@ static inline void enqueue_entity_load_avg(struct > > cfs_rq *cfs_rq, > > struct sched_entity *se, > > int wakeup) > > { > > - /* > > - * We track migrations using entity decay_count <= 0, on a wake-up > > - * migration we use a negative decay count to track the remote decays > > - * accumulated while sleeping. > > - * > > - * Newly forked tasks are enqueued with se->avg.decay_count == 0, they > > - * are seen by enqueue_entity_load_avg() as a migration with an already > > - * constructed load_avg_contrib. > > - */ > > - if (unlikely(se->avg.decay_count <= 0)) { > > + /* we track migrations using entity decay_count == 0 */ > > + if (unlikely(!se->avg.decay_count)) { > > se->avg.last_runnable_update = rq_clock_task(rq_of(cfs_rq)); > > - if (se->avg.decay_count) { > > - /* > > - * In a wake-up migration we have to approximate the > > - * time sleeping. This is because we can't synchronize > > - * clock_task between the two cpus, and it is not > > - * guaranteed to be read-safe. Instead, we can > > - * approximate this using our carried decays, which are > > - * explicitly atomically readable. > > - */ > > - se->avg.last_runnable_update -= (-se->avg.decay_count) > > - << 20; > > - update_entity_load_avg(se, 0); > > - /* Indicate that we're now synchronized and on-rq */ > > - se->avg.decay_count = 0; > > - } > > wakeup = 0; > > } else { > > __synchronize_entity_decay(se); > > @@ -5114,7 +5091,7 @@ migrate_task_rq_fair(struct task_struct *p, int > > next_cpu) > > * be negative here since on-rq tasks have decay-count == 0. > > */ > > if (se->avg.decay_count) { > > - se->avg.decay_count = -__synchronize_entity_decay(se); > > + __synchronize_entity_decay(se); > > atomic_long_add(se->avg.load_avg_contrib, > > &cfs_rq->removed_load); > > } > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [email protected] > 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
