From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751681AbbC0Edk (ORCPT ); Fri, 27 Mar 2015 00:33:40 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:57824 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbbC0Edj (ORCPT ); Fri, 27 Mar 2015 00:33:39 -0400 Message-ID: <5514DD91.8090505@linux.vnet.ibm.com> Date: Fri, 27 Mar 2015 10:03:21 +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: Wanpeng Li CC: peterz@infradead.org, 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, morten.rasmussen@arm.com, jason.low2@hp.com Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs References: <20150326130014.21532.17158.stgit@preeti.in.ibm.com> <20150327021201.GA4491@kernel> In-Reply-To: <20150327021201.GA4491@kernel> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15032704-0021-0000-0000-00000975C0F4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Wanpeng On 03/27/2015 07:42 AM, Wanpeng Li wrote: > Hi Preeti, > On Thu, Mar 26, 2015 at 06:32:44PM +0530, Preeti U Murthy wrote: >> >> 1. An ILB CPU was chosen from the first numa domain to trigger nohz idle >> load balancing [Given the experiment, upto 6 CPUs per core could be >> potentially idle in this domain.] >> >> 2. However the ILB CPU would call load_balance() on itself before >> initiating nohz idle load balancing. >> >> 3. Given cores are SMT8, the ILB CPU had enough opportunities to pull >> tasks from its sibling cores to even out load. >> >> 4. Now that the ILB CPU was no longer idle, it would abort nohz idle >> load balancing > > I don't see abort nohz idle load balancing when ILB CPU was no longer idle > in nohz_idle_balance(), could you explain more in details? When the ILB CPU pulls load in rebalance_domains(), its idle state is set to CPU_NOT_IDLE. "" idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE; And, When nohz_idle_balance() is called, the state of idle of ILB CPU is checked before proceeding with load balancing on idle CPUs. "" if (idle != CPU_IDLE || !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) goto end; You see that nohz idle balancing gets aborted. Regards Preeti U Murthy > > Regards, > Wanpeng Li >