Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751533AbbDAG2Y (ORCPT ); Wed, 1 Apr 2015 02:28:24 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:52543 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751030AbbDAG2X (ORCPT ); Wed, 1 Apr 2015 02:28:23 -0400 Message-ID: <551B8FF3.70608@linux.vnet.ibm.com> Date: Wed, 01 Apr 2015 11:58:03 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Jason Low , Morten Rasmussen CC: Peter Zijlstra , "mingo@kernel.org" , "riel@redhat.com" , "daniel.lezcano@linaro.org" , "vincent.guittot@linaro.org" , "srikar@linux.vnet.ibm.com" , "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" Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs References: <20150326130014.21532.17158.stgit@preeti.in.ibm.com> <20150327143839.GO18994@e105550-lin.cambridge.arm.com> <55158966.4050300@linux.vnet.ibm.com> <20150327175651.GR18994@e105550-lin.cambridge.arm.com> <20150330110632.GT23123@twins.programming.kicks-ass.net> <20150330120302.GT18994@e105550-lin.cambridge.arm.com> <551A61A9.6020009@linux.vnet.ibm.com> <1427823008.2492.19.camel@j-VirtualBox> In-Reply-To: <1427823008.2492.19.camel@j-VirtualBox> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15040106-8236-0000-0000-00000A7D476E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 39 On 03/31/2015 11:00 PM, Jason Low wrote: > On Tue, 2015-03-31 at 14:28 +0530, Preeti U Murthy wrote: > >> Morten, > >> I am a bit confused about the problem you are pointing to. > >> I am unable to see the issue. What is it that I am missing ? > > Hi Preeti, > > Here is one of the potential issues that have been described from my > understanding. > > In situations where there are just a few tasks to pull (for example, > there's 1 task to move). > > Before, if CPU 1 calls run_rebalance_domains(), we'll pull the tasks to > this CPU 1 (which is already awake) and run the task on CPU 1. > > Now, we'll pull the task to some idle CPU 2 and wake up CPU 2 in order > for the task to run. Meanwhile, CPU 1 may go idle, instead of running > the task on CPU 1 which was already awake. > Alright I see. But it is one additional wake up. And the wake up will be within the cluster. We will not wake up any CPU in the neighboring cluster unless there are tasks to be pulled. So, we can wake up a core out of a deep idle state and never a cluster in the problem described. In terms of energy efficiency, this is not so bad a scenario, is it? Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/