From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932217AbaIEMUJ (ORCPT ); Fri, 5 Sep 2014 08:20:09 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:36593 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751672AbaIEMUG (ORCPT ); Fri, 5 Sep 2014 08:20:06 -0400 Message-ID: <5409AA64.2010700@linux.vnet.ibm.com> Date: Fri, 05 Sep 2014 17:49:48 +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: Vincent Guittot CC: "peterz@infradead.org" , Ingo Molnar , Rik van Riel , Morten Rasmussen , LKML , Mike Galbraith , Nicolas Pitre , "daniel.lezcano@linaro.org" , Dietmar Eggemann , Kamalesh Babulal , Srikar Dronamraju Subject: Re: [QUERY] Confusing usage of rq->nr_running in load balancing References: <540707D9.4040208@linux.vnet.ibm.com> In-Reply-To: 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: 14090512-0320-0000-0000-00000067942D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vincent, On 09/03/2014 10:28 PM, Vincent Guittot wrote: > On 3 September 2014 14:21, Preeti U Murthy wrote: >> Hi, > > Hi Preeti, > >> >> There are places in kernel/sched/fair.c in the load balancing part where >> rq->nr_running is used as against cfs_rq->nr_running. At least I could >> not make out why the former was used in the following scenarios. >> It looks to me that it can very well lead to incorrect load balancing. >> Also I did not pay attention to the numa balancing part of the code >> while skimming through this file to catch this scenario. There are a >> couple of places there too which need to be scrutinized. >> >> 1. load_balance(): The check (busiest->nr_running > 1) >> The load balancing would be futile if there are tasks of other >> scheduling classes, wouldn't it? > > agree with you > >> >> 2. active_load_balance_cpu_stop(): A similar check and a similar >> consequence as 1 here. > > agree with you > >> >> 3. nohz_kick_needed() : We check for more than one task on the runqueue >> and hence trigger load balancing even if there are rt-tasks. > > I can see one potentiel reason why rq->nr_running is interesting that > is the group capacity might have changed because of non cfs tasks > since last load balance. So we need to monitor the change of the > groups' capacity to ensure that the average load of each group is > still in the same level > >> >> 4. cpu_avg_load_per_task(): This stands out among the rest as an >> incorrect usage of rq->nr_running in place of cfs_rq->nr_running. We >> divide the load associated with the cfs_rq by the number of tasks on the >> rq. This will make the cfs_rq load look smaller. > > This one is solved in the consolidation of cpu_capacity patchset Sorry, but I don't see where in your patchset you have addressed this issue. Can you please point out the patch? Regards Preeti U Murthy