linux-kernel - Re: [PATCH] sched: fix wrong rq's runnable

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Date:	Fri, 08 Feb 2013 09:46:18 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	peterz@...radead.org, mingo@...nel.org, pjt@...gle.com,
	fweisbec@...il.com
Subject: Re: [PATCH] sched: fix wrong rq's runnable_avg update with rt task

On Fri, 2013-02-08 at 12:11 +0100, Vincent Guittot wrote:
> When a RT task is scheduled on an idle CPU, the update of the rq's load is
> not done because CFS's functions are not called. Then, the idle_balance,
> which is called just before entering the idle function, updates the
> rq's load and makes the assumption that the elapsed time since the last
> update, was only running time.
> 
> The rq's load of a CPU that only runs a periodic RT task, is close to
> LOAD_AVG_MAX whatever the running duration of the RT task is.
> 
> A new idle_exit function is called when the prev task is the idle function
> so the elapsed time will be accounted as idle time in the rq's load.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/core.c  |    3 +++
>  kernel/sched/fair.c  |   10 ++++++++++
>  kernel/sched/sched.h |    5 +++++
>  3 files changed, 18 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 26058d0..592e06c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2927,6 +2927,9 @@ need_resched:
>  
>  	pre_schedule(rq, prev);
>  
> +	if (unlikely(prev == rq->idle))
> +		idle_exit(cpu, rq);
> +

Let's get rid of the added junk in the core code that should be isolated
in the idle code.

I posted these patches before, and I'm about to post again:

https://lkml.org/lkml/2012/12/21/378
https://lkml.org/lkml/2012/12/21/377

I'm working to clean these patches up today and post them again. Would
working on top of these work for you?

-- Steve


>  	if (unlikely(!rq->nr_running))
>  		idle_balance(cpu, rq);
>  


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