Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759075Ab3GaQb1 (ORCPT ); Wed, 31 Jul 2013 12:31:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45535 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754442Ab3GaQb0 (ORCPT ); Wed, 31 Jul 2013 12:31:26 -0400 Message-ID: <51F93121.5050802@redhat.com> Date: Wed, 31 Jul 2013 11:45:37 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Jason Low CC: Ingo Molnar , Peter Zijlstra , KML , Mike Galbraith , Thomas Gleixner , Paul Turner , Alex Shi , Preeti U Murthy , Vincent Guittot , Morten Rasmussen , Namhyung Kim , Andrew Morton , Kees Cook , Mel Gorman , aswin@hp.com, scott.norton@hp.com, chegu_vinod@hp.com, Srikar Dronamraju Subject: Re: [RFC PATCH] sched: Reduce overestimating avg_idle References: <1375263472.3922.26.camel@j-VirtualBox> In-Reply-To: <1375263472.3922.26.camel@j-VirtualBox> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2207 Lines: 43 On 07/31/2013 05:37 AM, Jason Low wrote: > The avg_idle value may sometimes be overestimated, which may cause new idle > load balance to be attempted more often than it should. Currently, when > avg_idle gets updated, if the delta exceeds some max value (default 1000000 ns), > the entire avg gets set to the max value, regardless of what the previous avg > was. So if a CPU remains idle for 200,000 ns most of the time, and if the CPU > goes idle for 1,200,000 ns, the average is then pushed up to 1,000,000 ns when > it should be less. > > Additionally, once the avg_idle is at its max, it may take a while to pull the > avg down to a value that it should be. In the above example, after the avg idle > is set the max value of 1000000 ns, the CPU's idle durations needs to > be 200000 ns for the next 8 occurrences before the avg falls below the migration > cost value. > > This patch attempts to avoid these situations by always updating the avg_idle > value first with the function call to update_avg(). Then, if the avg_idle > exceeds the max avg value, the avg gets set to the max. Also, this patch lowers > the max avg_idle value to migration_cost * 1.5 instead of migration_cost * 2 to > reduce the time it takes to pull the avg idle to a lower value after long idles. > > With this change, I got some decent performance boosts in AIM7 workloads on an > 8 socket machine on the 3.10 kernel. In particular, it boosted the AIM7 fserver > workload by about 20% when running it with a high # of users. > > An avg_idle related question that I have is does migration_cost in idle balance > need to be the same as the migration_cost in task_hot()? Can we keep > migration_cost default value used in task_hot() the same, but have a different > default value or increase migration_cost only when comparing it with avg_idle in > idle balance? > > > Signed-off-by: Jason Low Reviewed-by: Rik van Riel -- All rights reversed -- 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/