From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759471Ab3KMPRl (ORCPT ); Wed, 13 Nov 2013 10:17:41 -0500 Received: from merlin.infradead.org ([205.233.59.134]:60208 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753522Ab3KMPRj (ORCPT ); Wed, 13 Nov 2013 10:17:39 -0500 Date: Wed, 13 Nov 2013 16:17:18 +0100 From: Peter Zijlstra To: Srikar Dronamraju Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mikey@neuling.org, linux-tip-commits@vger.kernel.org Subject: Re: [PATCH v2] sched: Check sched_domain before computing group power. Message-ID: <20131113151718.GN21461@twins.programming.kicks-ass.net> References: <20131112105547.GA27310@linux.vnet.ibm.com> <20131112115736.GO5056@laptop.programming.kicks-ass.net> <20131112164126.GF2559@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131112164126.GF2559@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 12, 2013 at 10:11:26PM +0530, Srikar Dronamraju wrote: > After Commit-id 863bffc80898 (sched/fair: Fix group power_orig > computation), we might end up computing group power before the > sched_domain for a cpu is updated. > > Update with cpu_power, if rq->sd is not yet updated. > > Signed-off-by: Srikar Dronamraju > --- > Changelog since v1: Fix divide by zero errors that can result because > power/power_orig was set to 0. Duh yes!, init_sched_groups_power() is called before we attach the actual domains, so the above will _always_ fail for the build_sched_domain() case. I was a bit puzzled how we could ever have 0 since surely at least the current cpu should have some !0 contribution, but no! --- Subject: sched: Check sched_domain before computing group power From: Srikar Dronamraju Date: Tue, 12 Nov 2013 22:11:26 +0530 After Commit-id 863bffc80898 (sched/fair: Fix group power_orig computation), we can dereference rq->sd before its set. Fix this by falling back to power_of() in this case and add a comment explaining things. Cc: mikey@neuling.org Cc: mingo@kernel.org Cc: hpa@zytor.com Cc: tglx@linutronix.de Signed-off-by: Srikar Dronamraju [peterz: added comment and tweaked patch] Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131112164126.GF2559@linux.vnet.ibm.com --- kernel/sched/fair.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5354,10 +5354,31 @@ void update_group_power(struct sched_dom */ for_each_cpu(cpu, sched_group_cpus(sdg)) { - struct sched_group *sg = cpu_rq(cpu)->sd->groups; + struct sched_group_power *sgp; + struct rq *rq = cpu_rq(cpu); - power_orig += sg->sgp->power_orig; - power += sg->sgp->power; + /* + * build_sched_domains() -> init_sched_groups_power() + * gets here before we've attached the domains to the + * runqueues. + * + * Use power_of(), which is set irrespective of domains + * in update_cpu_power(). + * + * This avoids power/power_orig from being 0 and + * causing divide-by-zero issues on boot. + * + * Runtime updates will correct power_orig. + */ + if (!rq->sd) { + power_orig += power_of(cpu); + power += power_of(cpu); + continue; + } + + sgp = rq->sd->groups->sgp; + power_orig += sgp->power_orig; + power += sgp->power; } } else { /*