From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Thu, 29 May 2014 16:02:04 +0200
Subject: [PATCH v2 11/11] sched: replace capacity by activity
In-Reply-To: <1400860385-14555-12-git-send-email-vincent.guittot@linaro.org>
References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org>
 <1400860385-14555-12-git-send-email-vincent.guittot@linaro.org>
Message-ID: <20140529140204.GH11074@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 05:53:05PM +0200, Vincent Guittot wrote:
> @@ -6052,8 +6006,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>  		 * with a large weight task outweighs the tasks on the system).
>  		 */
>  		if (prefer_sibling && sds->local &&
> -		    sds->local_stat.group_has_capacity)
> -			sgs->group_capacity = min(sgs->group_capacity, 1U);
> +		    sds->local_stat.group_capacity > 0)
> +			sgs->group_capacity = min(sgs->group_capacity, 1L);
>  
>  		if (update_sd_pick_busiest(env, sds, sg, sgs)) {
>  			sds->busiest = sg;
> @@ -6228,7 +6182,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>  		 * have to drop below capacity to reach cpu-load equilibrium.
>  		 */
>  		load_above_capacity =
> -			(busiest->sum_nr_running - busiest->group_capacity);
> +			(busiest->sum_nr_running - busiest->group_weight);
>  
>  		load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_POWER_SCALE);
>  		load_above_capacity /= busiest->group_power;

I think you just broke PREFER_SIBLING here..

So we want PREFER_SIBLING to work on nr_running, not utilization because
we want to spread single tasks around, regardless of their utilization.