linux-kernel - Re: [PATCH v3] sched: keep quiescent cpu out of idle balance loop

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Message-ID: <1392975715.5451.118.camel@marge.simpson.net>
Date:	Fri, 21 Feb 2014 10:41:55 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Lei Wen <leiwen@...vell.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	preeti.lkml@...il.com, daniel.lezcano@...aro.org,
	viresh.kumar@...aro.org, xjian@...vell.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] sched: keep quiescent cpu out of idle balance loop

On Fri, 2014-02-21 at 17:15 +0800, Lei Wen wrote:

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 235cfa7..af30b6a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6883,6 +6883,14 @@ void nohz_balance_enter_idle(int cpu)
>  	if (!cpu_active(cpu))
>  		return;
>  
> +	/*
> +	 * If this cpu is isolated, its rq's sd member would becomes NULL.
> +	 * Base on this observation, we could exclude this cpu from nohz
> +	 * idle balance, so that it would not be disturbed.
> +	 */
> +	if (!this_rq()->sd)
> +		return;
> +
>  	if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
>  		return;

What about nohz_balance_exit_idle()?

I think Peter queued a patchlet to tell nohz balancing to go away.

-Mike

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