From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755248Ab0ETMOB (ORCPT ); Thu, 20 May 2010 08:14:01 -0400 Received: from isilmar-3.linta.de ([188.40.101.200]:48432 "EHLO linta.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754933Ab0ETMN7 (ORCPT ); Thu, 20 May 2010 08:13:59 -0400 Date: Thu, 20 May 2010 14:13:55 +0200 From: Dominik Brodowski To: Nigel Cunningham Cc: Nigel Cunningham , Suresh Siddha , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Arjan van de Ven , Venkatesh Pallipadi , Vaidyanathan Srinivasan , ego@in.ibm.com, LKML Subject: Re: [patch 0/7] sched: change nohz idle load balancing logic to push model Message-ID: <20100520121355.GA13163@isilmar-3.linta.de> Mail-Followup-To: Dominik Brodowski , Nigel Cunningham , Nigel Cunningham , Suresh Siddha , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Arjan van de Ven , Venkatesh Pallipadi , Vaidyanathan Srinivasan , ego@in.ibm.com, LKML References: <20100517182726.089700767@sbs-t61.sc.intel.com> <4BF517FE.1000103@tuxonice.net> <20100520111753.GA2264@isilmar-3.linta.de> <4BF51E93.4030601@crca.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BF51E93.4030601@crca.org.au> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey On Thu, May 20, 2010 at 09:35:47PM +1000, Nigel Cunningham wrote: > On 20/05/10 21:17, Dominik Brodowski wrote: >> Hey, >> >> On Thu, May 20, 2010 at 09:07:42PM +1000, Nigel Cunningham wrote: >>> "Load balancing tick" is still number one in my powertop list of top >>> causes of wakeups (sitting at ~60 to 80 per second as I type this, with >>> ~170 wakeups per second total). Comparing this to the numbers I posted >>> earlier, we seem to have a win. >>> >>> I do wonder, though, whether further work could still be done. If I take >>> one core offline, for example, I'm still getting load balancing ticks. >>> Intuitively, I'd expect there to be no need for them with only one core >>> available. But maybe I'm just ignorant of what's going on. >> >> Are you using HZ=1000, and is the CPU active ~ 6-8 % ? If so, is it just the >> regular timer tick while the CPU is active, and so not a real "wakeup"? (Or >> possibly double the number if both CPUs are active) > > HZ is 1000, and the CPU running percentage in Powertop is low (2% when > I'm not typing). Still, that'd count for up to 4 % of the reported ticks. On my system, this phenomenon accounts pretty much for the events powertop calls "load balancin ticks". I wonder whether user- or kernelspace should be more smart to not consider something a wakeup event if it wasn't a wakeup, i.e. to ignore timer events from timer_stat / powertop if the CPU wasn't actually idle... Best, Dominik