From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752657AbbC0NEN (ORCPT ); Fri, 27 Mar 2015 09:04:13 -0400 Received: from e28smtp07.in.ibm.com ([122.248.162.7]:47109 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752310AbbC0NEJ (ORCPT ); Fri, 27 Mar 2015 09:04:09 -0400 Date: Fri, 27 Mar 2015 18:33:55 +0530 From: Srikar Dronamraju To: Preeti U Murthy Cc: peterz@infradead.org, mingo@kernel.org, riel@redhat.com, daniel.lezcano@linaro.org, vincent.guittot@linaro.org, pjt@google.com, benh@kernel.crashing.org, efault@gmx.de, linux-kernel@vger.kernel.org, iamjoonsoo.kim@lge.com, svaidy@linux.vnet.ibm.com, tim.c.chen@linux.intel.com, morten.rasmussen@arm.com, jason.low2@hp.com Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs Message-ID: <20150327130355.GD6895@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20150326130014.21532.17158.stgit@preeti.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20150326130014.21532.17158.stgit@preeti.in.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15032713-0025-0000-0000-000003FCFB2B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > When a CPU is kicked to do nohz idle balancing, it wakes up to do load > balancing on itself, followed by load balancing on behalf of idle CPUs. > But it may end up with load after the load balancing attempt on itself. > This aborts nohz idle balancing. As a result several idle CPUs are left > without tasks till such a time that an ILB CPU finds it unfavorable to > pull tasks upon itself. This delays spreading of load across idle CPUs > and worse, clutters only a few CPUs with tasks. > [..... snipped .... ] > Fix this, by checking if a CPU was woken up to do nohz idle load > balancing, before it does load balancing upon itself. This way we allow > idle CPUs across the system to do load balancing which results in > quicker spread of load, instead of performing load balancing within the > local sched domain hierarchy of the ILB CPU alone under circumstances > such as above. > > Signed-off-by: Preeti U Murthy > --- Looks good to me. Reviewed-by: Srikar Dronamraju