linux-kernel - Re: [PATCH v4 2/6] sched: set initial value of runnable avg for new forked task

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Message-ID: <20130502110108.GA13494@dyad.programming.kicks-ass.net>
Date:	Thu, 2 May 2013 13:01:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	mingo@...hat.com, tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, morten.rasmussen@....com,
	vincent.guittot@...aro.org, gregkh@...uxfoundation.org,
	preeti@...ux.vnet.ibm.com, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, len.brown@...el.com,
	rafael.j.wysocki@...el.com, jkosina@...e.cz,
	clark.williams@...il.com, tony.luck@...el.com,
	keescook@...omium.org, mgorman@...e.de, riel@...hat.com
Subject: Re: [PATCH v4 2/6] sched: set initial value of runnable avg for
 new forked task

On Sat, Apr 27, 2013 at 01:25:40PM +0800, 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 <alex.shi@...el.com>

This patch seems sensible enough.. 

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

> ---
>  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 86e87f1..e0c003a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c

> +	/* New forked task assumed with full utilization */
> +#if defined(CONFIG_SMP)
> +	p->se.avg.load_avg_contrib = p->se.load.weight;
> +#endif

We'd typically write: #ifdef CONFIG_SMP
we only use the #if defined() form for multiple CONFIG tests.
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