From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752859Ab0C2OmG (ORCPT ); Mon, 29 Mar 2010 10:42:06 -0400 Received: from casper.infradead.org ([85.118.1.10]:48735 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022Ab0C2OmC (ORCPT ); Mon, 29 Mar 2010 10:42:02 -0400 Subject: Re: [REGRESSION 2.6.30][PATCH 1/1] sched: defer idle accounting till after load update period From: Peter Zijlstra To: Chase Douglas Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Andrew Morton , "Rafael J. Wysocki" In-Reply-To: <1269870072-22449-2-git-send-email-chase.douglas@canonical.com> References: <1269870072-22449-1-git-send-email-chase.douglas@canonical.com> <1269870072-22449-2-git-send-email-chase.douglas@canonical.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 29 Mar 2010 16:41:58 +0200 Message-ID: <1269873718.12097.342.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2010-03-29 at 09:41 -0400, Chase Douglas wrote: > There's a period of 10 ticks where calc_load_tasks is updated by all the > cpus for the load avg. Usually all the cpus do this during the first > tick. If any cpus go idle, calc_load_tasks is decremented accordingly. > However, if they wake up calc_load_tasks is not incremented. Thus, if > cpus go idle during the 10 tick period, calc_load_tasks may be > decremented to a non-representative value. This issue can lead to > systems having a load avg of exactly 0, even though the real load avg > could theoretically be up to NR_CPUS. > > This change defers calc_load_tasks accounting after each cpu updates the > count until after the 10 tick period. >>From reading the above changelog it seems to me there should be a callback from leaving nohz mode, your proposed patch has no such thing.