Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757007Ab3EGFDw (ORCPT ); Tue, 7 May 2013 01:03:52 -0400 Received: from mga03.intel.com ([143.182.124.21]:35340 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756506Ab3EGFDu (ORCPT ); Tue, 7 May 2013 01:03:50 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,625,1363158000"; d="scan'208";a="237858341" Message-ID: <51888B2D.30901@intel.com> Date: Tue, 07 May 2013 13:03:41 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Paul Turner 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 Subject: Re: [PATCH v5 3/7] sched: set initial value of runnable avg for new forked task References: <1367804711-30308-1-git-send-email-alex.shi@intel.com> <1367804711-30308-4-git-send-email-alex.shi@intel.com> <5187760D.8060900@intel.com> <51886460.3020009@intel.com> <51887404.4060102@intel.com> In-Reply-To: <51887404.4060102@intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4144 Lines: 119 On 05/07/2013 11:24 AM, Alex Shi wrote: >> > The reason to store a small initial "observation" here is so that as >> > when we reach our next period edge our load converges (presumably >> > down) towards its true target more smoothly; as well as providing a >> > task additional protection from being considered "small" through >> > start-up. >> > > It will give new forked task 1 ms extra running time. That will bring > incorrect info if the new forked goes to sleep a while. > But this info should benefit to some benchmarks like aim7, > pthread_cond_broadcast. So I am convinced. :) > > What's your opinion of this, Peter? Here is the patch according to Paul's opinions. just refer the __update_task_entity_contrib in sched.h looks ugly. comments are appreciated! --- >From 647404447c996507b6a94110ed13fd122e4ee154 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Mon, 3 Dec 2012 17:30:39 +0800 Subject: [PATCH 3/7] sched: set initial value of runnable avg for new forked task 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 give initial value of runnable_avg_sum/period to resolve such issues. Thanks for Pual's suggestions Signed-off-by: Alex Shi --- kernel/sched/core.c | 8 +++++++- kernel/sched/fair.c | 4 ++++ kernel/sched/sched.h | 1 + 3 files changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c8db984..4e78de1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1566,6 +1566,11 @@ 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; + /* New forked task assumed with full utilization */ + p->se.avg.runnable_avg_period = 1024; + p->se.avg.runnable_avg_sum = 1024; + __update_task_entity_contrib(&p->se); #endif #ifdef CONFIG_SCHEDSTATS memset(&p->se.statistics, 0, sizeof(p->se.statistics)); @@ -1619,7 +1624,6 @@ void sched_fork(struct task_struct *p) unsigned long flags; int cpu = get_cpu(); - __sched_fork(p); /* * We mark the process as running here. This guarantees that * nobody will actually run it, and a signal or other external @@ -1653,6 +1657,8 @@ void sched_fork(struct task_struct *p) p->sched_reset_on_fork = 0; } + __sched_fork(p); + 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; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c6634f1..ec4cb9b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -876,6 +876,7 @@ extern const struct sched_class idle_sched_class; extern void trigger_load_balance(struct rq *rq, int cpu); extern void idle_balance(int this_cpu, struct rq *this_rq); +extern inline void __update_task_entity_contrib(struct sched_entity *se); #else /* CONFIG_SMP */ static inline void idle_balance(int cpu, struct rq *rq) -- 1.7.12 -- Thanks Alex -- 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/