From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Thu, 29 May 2014 16:04:27 +0200
Subject: [PATCH v2 10/11] sched: move cfs task on a CPU with higher
 capacity
In-Reply-To: <1400860385-14555-11-git-send-email-vincent.guittot@linaro.org>
References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org>
 <1400860385-14555-11-git-send-email-vincent.guittot@linaro.org>
Message-ID: <20140529140427.GI11074@laptop.programming.kicks-ass.net>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, May 23, 2014 at 05:53:04PM +0200, Vincent Guittot wrote:
> @@ -7282,6 +7289,12 @@ static inline int nohz_kick_needed(struct rq *rq)
>  
>  		if (nr_busy > 1)
>  			goto need_kick_unlock;
> +
> +		if ((rq->cfs.h_nr_running >= 1)
> +		 && ((rq->cpu_power * sd->imbalance_pct) <
> +					(rq->cpu_power_orig * 100)))
> +			goto need_kick_unlock;
> +
>  	}
>  
>  	sd = rcu_dereference(per_cpu(sd_asym, cpu));

So what happens when a cpu is consistently low on power (say due to a
pinned RT task) the balancer would quickly adjust the load level, but
this would endlessly kick things into action, even though we're balanced
just fine.