linux-kernel - Re: [PATCH] sched/fair: Fix sched_entity::avg::decay

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Message-ID: <xm26vblc7osr.fsf@sword-of-the-dawn.mtv.corp.google.com>
Date:	Mon, 15 Dec 2014 10:25:56 -0800
From:	bsegall@...gle.com
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	<linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Kirill Tkhai <tkhai@...dex.ru>,
	pjt@...gle.com
Subject: Re: [PATCH] sched/fair: Fix sched_entity::avg::decay_count initialization

Kirill Tkhai <ktkhai@...allels.com> writes:

> Child has the same decay_count as parent. If it's not zero,
> we add it to parent's cfs_rq->removed_load:
>
> wake_up_new_task()->set_task_cpu()->migrate_task_rq_fair().
>
> Child's load is a just garbade after copying of parent,
> it hasn't been on cfs_rq yet, and it must not be added to
> cfs_rq::removed_load in migrate_task_rq_fair().
>
> The patch moves sched_entity::avg::decay_count intialization
> in sched_fork(). So, migrate_task_rq_fair() does not change
> removed_load.
>
> Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>

Reviewed-by: Ben Segall <bsegall@...gle.com>

> ---
>  kernel/sched/core.c |    1 +
>  kernel/sched/fair.c |    1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index bb398c0..2894b69 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1832,6 +1832,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	p->se.prev_sum_exec_runtime	= 0;
>  	p->se.nr_migrations		= 0;
>  	p->se.vruntime			= 0;
> +	p->se.avg.decay_count		= 0;
>  	INIT_LIST_HEAD(&p->se.group_node);
>  
>  #ifdef CONFIG_SCHEDSTATS
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index df2cdf7..5f3b5a7 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -676,7 +676,6 @@ void init_task_runnable_average(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;
>
>
>
> --
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