linux-kernel - Re: [patch v6 03/21] sched: only count runnable avg on cfs_rq's nr

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Date:	Wed, 03 Apr 2013 09:02:17 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>, Paul Turner <pjt@...gle.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>, gregkh@...uxfoundation.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch v6 03/21] sched: only count runnable avg on cfs_rq's nr_running

On 04/02/2013 10:30 PM, Vincent Guittot wrote:
> On 30 March 2013 15:34, Alex Shi <alex.shi@...el.com> wrote:
>> Old function count the runnable avg on rq's nr_running even there is
>> only rt task in rq. That is incorrect, so correct it to cfs_rq's
>> nr_running.
>>
>> Signed-off-by: Alex Shi <alex.shi@...el.com>
>> ---
>>  kernel/sched/fair.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 2881d42..026e959 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -2829,7 +2829,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>>         }
>>
>>         if (!se) {
>> -               update_rq_runnable_avg(rq, rq->nr_running);
>> +               update_rq_runnable_avg(rq, rq->cfs.nr_running);
> 
> A RT task that preempts your CFS task will be accounted in the
> runnable_avg fields. So whatever you do, RT task will impact your
> runnable_avg statistics. Instead of trying to get only CFS tasks, you
> should take into account all tasks activity in the rq.

Thanks for comments, Vincent!

Yes, I know some rt task time was counted into cfs, but now we have no
good idea to remove them clearly. So I just want to a bit more precise
cfs runnable load here.
On the other side, periodic LB balance on combined the cfs/rt load, but
removed the RT utilisation in cpu_power.

So, PJT, Peter, what's your idea of this point?
> 
> Vincent
>>                 inc_nr_running(rq);
>>         }
>>         hrtick_update(rq);
>> --
>> 1.7.12
>>


-- 
Thanks Alex
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