From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753666AbcGDRnS (ORCPT ); Mon, 4 Jul 2016 13:43:18 -0400 Received: from mail-wm0-f48.google.com ([74.125.82.48]:38504 "EHLO mail-wm0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750734AbcGDRnR (ORCPT ); Mon, 4 Jul 2016 13:43:17 -0400 Message-ID: <1467654194.3583.33.camel@gmail.com> Subject: Re: [rfc patch] sched/fair: Use instantaneous load for fork/exec balancing From: Mike Galbraith To: Matt Fleming , Dietmar Eggemann Cc: Peter Zijlstra , Yuyang Du , LKML , Mel Gorman Date: Mon, 04 Jul 2016 19:43:14 +0200 In-Reply-To: <20160704150452.GP8415@codeblueprint.co.uk> References: <1465891111.1694.13.camel@gmail.com> <5760115C.7040306@arm.com> <1465922407.3626.21.camel@gmail.com> <5761752A.6000606@arm.com> <20160704150452.GP8415@codeblueprint.co.uk> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2016-07-04 at 16:04 +0100, Matt Fleming wrote: > But we can optimise the special case of dequeueing the last entity and > reset ::runnable_load_avg early, which gives a performance improvement > to workloads that trigger the load balancer, such as fork-heavy > applications when SD_BALANCE_FORK is set, because it gives a more up > to date view of how busy the cpu is. Begs the question: what's so special about this case vs any other dequeue/enqueue? I've given up on this as being a waste of time. Either you serialize everything box wide (not!) and can then make truly accurate evaluations of state, or you're making an educated guess based upon what once was. The only place I've seen where using the average consistently has issues is with a longish period periodic load (schbench). -Mike