From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752485AbbCXPVg (ORCPT <rfc822;w@1wt.eu>);
	Tue, 24 Mar 2015 11:21:36 -0400
Received: from bombadil.infradead.org ([198.137.202.9]:46224 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751980AbbCXPVc (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 24 Mar 2015 11:21:32 -0400
Date: Tue, 24 Mar 2015 16:21:04 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: mingo@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        yuyang.du@intel.com, preeti@linux.vnet.ibm.com, mturquette@linaro.org,
        nico@linaro.org, rjw@rjwysocki.net, juri.lelli@arm.com,
        linux-kernel@vger.kernel.org
Subject: Re: [RFCv3 PATCH 42/48] sched: Introduce energy awareness into
 find_busiest_queue
Message-ID: <20150324152104.GP21418@twins.programming.kicks-ass.net>
References: <1423074685-6336-1-git-send-email-morten.rasmussen@arm.com>
 <1423074685-6336-43-git-send-email-morten.rasmussen@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1423074685-6336-43-git-send-email-morten.rasmussen@arm.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Feb 04, 2015 at 06:31:19PM +0000, Morten Rasmussen wrote:
> +++ b/kernel/sched/fair.c
> @@ -7216,6 +7216,37 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>  	unsigned long busiest_load = 0, busiest_capacity = 1;
>  	int i;
>  
> +	if (env->use_ea) {
> +		struct rq *costliest = NULL;
> +		unsigned long costliest_usage = 1024, costliest_energy = 1;
> +
> +		for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
> +			unsigned long usage = get_cpu_usage(i);
> +			struct rq *rq = cpu_rq(i);
> +			struct sched_domain *sd = rcu_dereference(rq->sd);
> +			struct energy_env eenv = {
> +				.sg_top = sd->groups,
> +				.usage_delta    = 0,
> +				.src_cpu        = -1,
> +				.dst_cpu        = -1,
> +			};
> +			unsigned long energy = sched_group_energy(&eenv);
> +
> +			/*
> +			 * We're looking for the minimal cpu efficiency
> +			 * min(u_i / e_i), crosswise multiplication leads to
> +			 * u_i * e_j < u_j * e_i with j as previous minimum.
> +			 */
> +			if (usage * costliest_energy < costliest_usage * energy) {
> +				costliest_usage = usage;
> +				costliest_energy = energy;
> +				costliest = rq;
> +			}
> +		}
> +
> +		return costliest;
> +	}
> +
>  	for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
>  		unsigned long capacity, wl;
>  		enum fbq_type rt;

So I've thought about parametrizing the whole load balance thing to
avoid things like this.

Irrespective of whether we balance on pure load or another metric we
have the same structure, only different units plugged in.

I've not really spend too much time on it to see what it would look
like, but I think it would be a good avenue to investigate to avoid
patches like this.