From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757014Ab3ILSG5 (ORCPT ); Thu, 12 Sep 2013 14:06:57 -0400 Received: from terminus.zytor.com ([198.137.202.10]:37987 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756959Ab3ILSGl (ORCPT ); Thu, 12 Sep 2013 14:06:41 -0400 Date: Thu, 12 Sep 2013 11:06:06 -0700 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, vincent.guitto@linaro.org, hpa@zytor.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, vincent.guitto@linaro.org, linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/fair: Fix the group_capacity computation Git-Commit-ID: c61037e905a5cb74c7d786c35ee2cdbab9ed63af X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Thu, 12 Sep 2013 11:06:13 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c61037e905a5cb74c7d786c35ee2cdbab9ed63af Gitweb: http://git.kernel.org/tip/c61037e905a5cb74c7d786c35ee2cdbab9ed63af Author: Peter Zijlstra AuthorDate: Wed, 28 Aug 2013 12:40:38 +0200 Committer: Ingo Molnar CommitDate: Thu, 12 Sep 2013 19:14:45 +0200 sched/fair: Fix the group_capacity computation Do away with 'phantom' cores due to N*frac(smt_power) >= 1 by limiting the capacity to the actual number of cores. The assumption of 1 < smt_power < 2 is an actual requirement because of what SMT is so this should work regardless of the SMT implementation. It can still be defeated by creative use of cpu hotplug, but if you're one of those freaks, you get to live with it. Signed-off-by: Peter Zijlstra Acked-by: Vincent Guittot Link: http://lkml.kernel.org/n/tip-dczmbi8tfgixacg1ji2av1un@git.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 218f9c5..51c5c3e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4556,18 +4556,24 @@ static inline int sg_imbalanced(struct sched_group *group) /* * Compute the group capacity. * - * For now the capacity is simply the number of power units in the group_power. - * A power unit represents a full core. - * - * This has an issue where N*frac(smt_power) >= 1, in that case we'll see extra - * 'cores' that aren't actually there. + * Avoid the issue where N*frac(smt_power) >= 1 creates 'phantom' cores by + * first dividing out the smt factor and computing the actual number of cores + * and limit power unit capacity with that. */ static inline int sg_capacity(struct lb_env *env, struct sched_group *group) { + unsigned int capacity, smt, cpus; + unsigned int power, power_orig; + + power = group->sgp->power; + power_orig = group->sgp->power_orig; + cpus = group->group_weight; - unsigned int power = group->sgp->power; - unsigned int capacity = DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE); + /* smt := ceil(cpus / power), assumes: 1 < smt_power < 2 */ + smt = DIV_ROUND_UP(SCHED_POWER_SCALE * cpus, power_orig); + capacity = cpus / smt; /* cores */ + capacity = min_t(unsigned, capacity, DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE)); if (!capacity) capacity = fix_small_capacity(env->sd, group);