From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755096Ab0JNO6i (ORCPT ); Thu, 14 Oct 2010 10:58:38 -0400 Received: from mailhost-r5-p2.mangoosta.org ([195.5.209.65]:58858 "EHLO smtp-delay1.nerim.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754185Ab0JNO6h (ORCPT ); Thu, 14 Oct 2010 10:58:37 -0400 Date: Thu, 14 Oct 2010 16:58:13 +0200 From: Damien Wyart To: Peter Zijlstra , Chase Douglas , Ingo Molnar , tmhikaru@gmail.com, Thomas Gleixner Cc: linux-kernel@vger.kernel.org Subject: Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later) Message-ID: <20101014145813.GA2185@brouette> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100929070153.GA2200@brouette> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, > With 2.6.36-rc6, I'm seeing a load of around 0.60 when the machine is > completely idle. This is similar to what someone reported for the latest > 2.6.35.x stables. This is on a core i7 machine, but I've no time to > bisect or test earlier versions right now, but I guess this is easy to > reproduce on the same plateform. After further investigation and cross-checking with the thread "PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later", I came to the following results: - the commit 74f5187ac873042f502227701ed1727e7c5fbfa9 isolated by Tim seems to be the culprit; - reverting it solves the problem with 2.6.36-rc7 in NOHZ mode: the load when idle goes down to 0.00 (which it never does with the patch applied) - using nohz=no with the commit reverted still gives correct behaviour (tested just in case) - vanilla 2.6.36-rc7 with this commit applied has the problem (load is around 0.60 when machine idle, sometimes less after several hours of uptime, but never 0.00), and rebooting with nohz=no makes the problem disappear: load goes down to 0.00 quickly after boot process has finished. I hope this answers the questions raised in the Tim's thread. Could someone with knowledge of the commit take a look at the problem? It would be a bit annoying to have this problem in 2.6.36, since Tim's initial report dates back to 2 weeks ago... I can help for further testing if needed. Thanks in advance, -- Damien