linux-kernel - Re: [PATCH] sched: Give idle_balance() a break when it does not move tasks.

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Date:	Mon, 12 Aug 2013 16:30:45 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Jason Low <jason.low2@...com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	aswin@...com, scott.norton@...com, chegu_vinod@...com,
	"Bui, Tuan" <tuan.d.bui@...com>, Waiman Long <Waiman.Long@...com>,
	"Makphaibulchoke, Thavatchai" <thavatchai.makpahibulchoke@...com>,
	"Bueso, Davidlohr" <davidlohr.bueso@...com>
Subject: Re: [PATCH] sched: Give idle_balance() a break when it does not move
 tasks.

>  	/*
> @@ -5298,6 +5300,8 @@ void idle_balance(int this_cpu, struct rq *this_rq)
>  			continue;
> 
>  		if (sd->flags & SD_BALANCE_NEWIDLE) {
> +			load_balance_attempted = true;
> +
>  			/* If we've pulled tasks over stop searching: */
>  			pulled_task = load_balance(this_cpu, this_rq,
>  						   sd, CPU_NEWLY_IDLE, &balance);
> @@ -5322,6 +5326,10 @@ void idle_balance(int this_cpu, struct rq *this_rq)
>  		 */
>  		this_rq->next_balance = next_balance;
>  	}
> +
> +	/* Give idle balance on this CPU a break when it isn't moving tasks */
> +	if (load_balance_attempted && !pulled_task)
> +		this_rq->next_newidle_balance = jiffies + (HZ / 100);
>  }

Looks reasonable. However should we do this per sd and not per rq. i.e
move the next_newidle_balance to sched_domain. So if we find a
load_balance in newly_idle context that wasn't successful, we skip
load_balance for that sd in the next newly idle balance.

-- 
Thanks and Regards
Srikar Dronamraju

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