linux-kernel - Re: [PATCH v4] sched: fix wrong rq's runnable

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Message-ID: <CAKfTPtAHVreu_PcyM3g_q0smBM3P0N=miJG36x6+JWYutLgA5w@mail.gmail.com>
Date:	Wed, 10 Apr 2013 09:59:11 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH v4] sched: fix wrong rq's runnable_avg update with rt tasks

On 10 April 2013 09:26, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2013-04-09 at 11:06 +0200, Vincent Guittot wrote:
>> >> +void idle_enter(struct rq *this_rq)
>> >> +{
>> >> +       update_rq_runnable_avg(this_rq, 1);
>> >> +}
>
>> >> +void idle_exit(struct rq *this_rq)
>> >> +{
>> >> +       update_rq_runnable_avg(this_rq, 0);
>> >> +}
>> >
>> > These seem like fairly unfortunate names to expose to the global
>> > namespace, why not expose update_rq_runnable_avg() instead?
>>
>> Just to gather in one place all cfs actions that should be done when
>> exiting idle even if we only have update_rq_runnable_avg right now. I
>> have distinguished that from idle_balance because this sequence can't
>> generate extra context switch like idle_balance and they would finally
>> not be called in the same time
>
> OK, but could we then please give then more scheduler specific names?
> It just seems to me that idle_enter/idle_exit() are very obvious
> function names for unrelated things.
>
> How about calling it idle_{enter,exit}_fair; so that once other classes
> grow hooks we can do something like:

My primary goal was to align with idle_balance name but
idle_{enter,exit}_fair is better

In the same way, should we change idle_balance to idle_balance_fair ?

and since we don't have Steve's irq constraint anymore, we could move
idle_balance in the beginning of the function pick_next_task_fair ? We
will not have spurious switch context and we will remove fair function
from __schedule function

Vincent
>
> static void pre_schedule_idle(struct rq *rq, struct task_struct *p)
> {
>         struct sched_class *class;
>
>         for_each_class(class) {
>                 if (class->idle_enter)
>                         class->idle_enter(rq);
>         }
> }
>
> or whatnot..
>
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