linux-kernel - Re: [PATCH] sched: Fast idling of CPU when system is partially loaded

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Date:	Fri, 13 Jun 2014 13:17:04 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Jason Low <jason.low2@...com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueson <davidlohr@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Fast idling of CPU when system is partially
 loaded

On Fri, 2014-06-13 at 12:18 -0700, Jason Low wrote:

> 
> I see. In that case, if a CPU is going idle, it still needs to call
> idle_balance() to update rq->idle_stamp and rq->next_balance (even if we
> skip calling the expensive load_balance).
> 
> What do you think about moving the overload check to the top of
> idle_balance():
> 
>         this_rq->idle_stamp = rq_clock(this_rq);
>  
> -       if (this_rq->avg_idle < sysctl_sched_migration_cost) {
> +       if (this_rq->avg_idle < sysctl_sched_migration_cost ||
> +           !this_rq->rd->overload) {
>                 rcu_read_lock();
>                 sd = rcu_dereference_check_sched_domain(this_rq->sd);
>                 if (sd)
> 
> 

That's a good point.  I think moving the check as you suggested
is appropriate.  I'll update the code in my next version.

Tim

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