Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751995Ab3FNKCs (ORCPT ); Fri, 14 Jun 2013 06:02:48 -0400 Received: from mail-lb0-f170.google.com ([209.85.217.170]:54312 "EHLO mail-lb0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751497Ab3FNKCq (ORCPT ); Fri, 14 Jun 2013 06:02:46 -0400 MIME-Version: 1.0 In-Reply-To: <1370589652-24549-4-git-send-email-alex.shi@intel.com> References: <1370589652-24549-1-git-send-email-alex.shi@intel.com> <1370589652-24549-4-git-send-email-alex.shi@intel.com> Date: Fri, 14 Jun 2013 18:02:45 +0800 Message-ID: Subject: Re: [patch v8 3/9] sched: set initial value of runnable avg for new forked task From: Lei Wen To: Alex Shi Cc: mingo@redhat.com, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, bp@alien8.de, pjt@google.com, namhyung@kernel.org, efault@gmx.de, morten.rasmussen@arm.com, vincent.guittot@linaro.org, preeti@linux.vnet.ibm.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, mgorman@suse.de, riel@redhat.com, wangyun@linux.vnet.ibm.com, Jason Low , Changlong Xie , sgruszka@redhat.com, fweisbec@gmail.com 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: 4860 Lines: 134 Hi Alex, On Fri, Jun 7, 2013 at 3:20 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. > > Further more, Morten Rasmussen notice some tasks were not launched at > once after created. So Paul and Peter suggest giving a start value for > new task runnable avg time same as sched_slice(). I am confused at this comment, how set slice to runnable avg would change the behavior of "some tasks were not launched at once after created"? IMHO, I could only tell that for the new forked task, it could be run if current task already be set as need_resched, and preempt_schedule or preempt_schedule_irq is called. Since the set slice to avg behavior would not affect this task's vruntime, and hence cannot make current running task be need_sched, if previously it cannot. Could you help correct if I am wrong at somewhere? .... Thanks, Lei > > Signed-off-by: Alex Shi > --- > kernel/sched/core.c | 6 ++---- > kernel/sched/fair.c | 23 +++++++++++++++++++++++ > kernel/sched/sched.h | 2 ++ > 3 files changed, 27 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b9e7036..6f226c2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1598,10 +1598,6 @@ static void __sched_fork(struct task_struct *p) > p->se.vruntime = 0; > INIT_LIST_HEAD(&p->se.group_node); > > -#ifdef CONFIG_SMP > - p->se.avg.runnable_avg_period = 0; > - p->se.avg.runnable_avg_sum = 0; > -#endif > #ifdef CONFIG_SCHEDSTATS > memset(&p->se.statistics, 0, sizeof(p->se.statistics)); > #endif > @@ -1745,6 +1741,8 @@ void wake_up_new_task(struct task_struct *p) > set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0)); > #endif > > + /* Give new task start runnable values */ > + set_task_runnable_avg(p); > rq = __task_rq_lock(p); > activate_task(rq, p, 0); > p->on_rq = 1; > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f404468..1fc30b9 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -680,6 +680,26 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se) > return calc_delta_fair(sched_slice(cfs_rq, se), se); > } > > +#ifdef CONFIG_SMP > +static inline void __update_task_entity_contrib(struct sched_entity *se); > + > +/* Give new task start runnable values to heavy its load in infant time */ > +void set_task_runnable_avg(struct task_struct *p) > +{ > + u32 slice; > + > + p->se.avg.decay_count = 0; > + slice = sched_slice(task_cfs_rq(p), &p->se) >> 10; > + p->se.avg.runnable_avg_sum = slice; > + p->se.avg.runnable_avg_period = slice; > + __update_task_entity_contrib(&p->se); > +} > +#else > +void set_task_runnable_avg(struct task_struct *p) > +{ > +} > +#endif > + > /* > * Update the current task's runtime statistics. Skip current tasks that > * are not in our scheduling class. > @@ -1527,6 +1547,9 @@ 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 direct. > */ > if (unlikely(se->avg.decay_count <= 0)) { > se->avg.last_runnable_update = rq_clock_task(rq_of(cfs_rq)); > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 24b1503..8bc66c6 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1058,6 +1058,8 @@ extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime > > extern void update_idle_cpu_load(struct rq *this_rq); > > +extern void set_task_runnable_avg(struct task_struct *p); > + > #ifdef CONFIG_PARAVIRT > static inline u64 steal_ticks(u64 steal) > { > -- > 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/ -- 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/