Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752098AbbGSGDM (ORCPT ); Sun, 19 Jul 2015 02:03:12 -0400 Received: from LGEMRELSE7Q.lge.com ([156.147.1.151]:56647 "EHLO lgemrelse7q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751090AbbGSGDK (ORCPT ); Sun, 19 Jul 2015 02:03:10 -0400 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Sun, 19 Jul 2015 15:03:03 +0900 From: Byungchul Park To: bsegall@google.com Cc: pjt@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: prevent sched entity from being decayed twice when both waking and migrating it Message-ID: <20150719060303.GE3956@byungchulpark-X58A-UD3R> References: <1437034317-15120-1-git-send-email-byungchul.park@lge.com> <20150717061949.GD3956@byungchulpark-X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5937 Lines: 146 On Fri, Jul 17, 2015 at 10:02:22AM -0700, bsegall@google.com wrote: > Byungchul Park writes: > > > On Thu, Jul 16, 2015 at 10:00:00AM -0700, bsegall@google.com wrote: > > > > hello, > > > >> byungchul.park@lge.com writes: > >> > >> > From: Byungchul Park > >> > > >> > 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? > > load_avg_contrib is computed from runnable_avg, which is not updated by > __synchronize_entity_decay, only by update_entity_load_avg -> > __update_entity_runnable_avg. __synchronize_entity_decay is used in this path > because update_entity_load_avg needs the rq lock (along with some other > reasons), and migrate_task_rq_fair generally doesn't have the lock. hello ben, i see... i missed the fact that __synchronize_entity_decay() is only for blocked one. i am sorry for bothering you. ;( thank you very much, byungchul > > > > > thanks, > > byungchul > > > >> > >> > > >> > --------------->8--------------- > >> > From 793c963d0b29977a0f6f9330291a9ea469cc54f0 Mon Sep 17 00:00:00 2001 > >> > From: Byungchul Park > >> > 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 > >> > --- > >> > 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 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/ > -- > 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/ -- 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/