[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. update_entity_load_avg() accounts that (approximation of) time blocked 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). > > --------------->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/
