From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755031AbaJUOyk (ORCPT ); Tue, 21 Oct 2014 10:54:40 -0400 Received: from casper.infradead.org ([85.118.1.10]:52198 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751180AbaJUOyi (ORCPT ); Tue, 21 Oct 2014 10:54:38 -0400 Date: Tue, 21 Oct 2014 16:54:35 +0200 From: Peter Zijlstra To: Yuyang Du Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, pjt@google.com, bsegall@google.com, arjan.van.de.ven@intel.com, len.brown@intel.com, rafael.j.wysocki@intel.com, alan.cox@intel.com, mark.gross@intel.com, fengguang.wu@intel.com Subject: Re: [RESEND PATCH 2/3 v5] sched: Rewrite per entity runnable load average tracking Message-ID: <20141021145435.GA23531@worktop.programming.kicks-ass.net> References: <1412907717-2871-1-git-send-email-yuyang.du@intel.com> <1412907717-2871-3-git-send-email-yuyang.du@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412907717-2871-3-git-send-email-yuyang.du@intel.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 10, 2014 at 10:21:56AM +0800, Yuyang Du wrote: > /* > + * Updating tg's load_avg is necessary before update_cfs_share (which is done) > + * and effective_load (which is not done because it is too costly). > */ > +static inline void update_tg_load_avg(struct cfs_rq *cfs_rq) > { > + long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib; > > + if (abs(delta) > cfs_rq->tg_load_avg_contrib / 64) { > + atomic_long_add(delta, &cfs_rq->tg->load_avg); > + cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg; > } > } In the thread here: lkml.kernel.org/r/1409094682.29189.23.camel@j-VirtualBox there are concerns about the error bounds of such constructs. We can basically 'leak' nr_cpus * threshold, which is potentially a very large number. Do we want to introduce the force updated to combat this?