Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752219Ab3EFIUF (ORCPT ); Mon, 6 May 2013 04:20:05 -0400 Received: from mail-lb0-f182.google.com ([209.85.217.182]:37987 "EHLO mail-lb0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751592Ab3EFIUD (ORCPT ); Mon, 6 May 2013 04:20:03 -0400 MIME-Version: 1.0 In-Reply-To: <1367804711-30308-4-git-send-email-alex.shi@intel.com> References: <1367804711-30308-1-git-send-email-alex.shi@intel.com> <1367804711-30308-4-git-send-email-alex.shi@intel.com> From: Paul Turner Date: Mon, 6 May 2013 01:19:30 -0700 Message-ID: Subject: Re: [PATCH v5 3/7] sched: set initial value of runnable avg for new forked task To: Alex Shi Cc: Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Andrew Morton , Borislav Petkov , Namhyung Kim , Mike Galbraith , Morten Rasmussen , Vincent Guittot , Preeti U Murthy , Viresh Kumar , LKML , Mel Gorman , Rik van Riel , Michael Wang Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3066 Lines: 83 On Sun, May 5, 2013 at 6:45 PM, Alex Shi wrote: > We need initialize the se.avg.{decay_count, load_avg_contrib} for a > new forked task. > Otherwise random values of above variables cause mess when do new task > enqueue: > enqueue_task_fair > enqueue_entity > enqueue_entity_load_avg > > and make forking balancing imbalance since incorrect load_avg_contrib. > > set avg.decay_count = 0, and avg.load_avg_contrib = se->load.weight to > resolve such issues. > > Signed-off-by: Alex Shi > --- > kernel/sched/core.c | 6 ++++++ > kernel/sched/fair.c | 4 ++++ > 2 files changed, 10 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index c8db984..ecec7f1 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1566,6 +1566,7 @@ static void __sched_fork(struct task_struct *p) > #ifdef CONFIG_SMP > p->se.avg.runnable_avg_period = 0; > p->se.avg.runnable_avg_sum = 0; > + p->se.avg.decay_count = 0; > #endif > #ifdef CONFIG_SCHEDSTATS > memset(&p->se.statistics, 0, sizeof(p->se.statistics)); > @@ -1653,6 +1654,11 @@ void sched_fork(struct task_struct *p) > p->sched_reset_on_fork = 0; > } > > + /* New forked task assumed with full utilization */ > +#if defined(CONFIG_SMP) > + p->se.avg.load_avg_contrib = p->se.load.weight; This is missing a scale_load() right? Further: Why not put this in __sched_fork? We should also charge a minimum period to make the numbers a little more kosher, e.g.: + p->se.avg.runnable_avg_period = 1024; + p->se.avg.runnable_avg_sum = 1024; Rather than exposing the representation of load_avg_contrib to __sched_fork it might also be better to call: __update_task_entity_contrib(&p->se) After the initialization above; this would also avoid potential bugs like the missing scale_load() above. > +#endif > + > if (!rt_prio(p->prio)) > p->sched_class = &fair_sched_class; > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 9c2f726..2881d42 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1508,6 +1508,10 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq, > * 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. > + * > + * When enqueue a new forked task, the se->avg.decay_count == 0, so > + * we bypass update_entity_load_avg(), use avg.load_avg_contrib initial > + * value: se->load.weight. > */ > if (unlikely(se->avg.decay_count <= 0)) { > se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task; > -- > 1.7.12 > -- 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/