Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754807AbZCQOAG (ORCPT ); Tue, 17 Mar 2009 10:00:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751700AbZCQN7y (ORCPT ); Tue, 17 Mar 2009 09:59:54 -0400 Received: from e28smtp08.in.ibm.com ([59.145.155.8]:45709 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751703AbZCQN7x (ORCPT ); Tue, 17 Mar 2009 09:59:53 -0400 Date: Tue, 17 Mar 2009 19:29:38 +0530 From: Balbir Singh To: Peter Zijlstra Cc: Bharata B Rao , Li Zefan , linux-kernel@vger.kernel.org, Dhaval Giani , Paul Menage , Ingo Molnar , KAMEZAWA Hiroyuki Subject: Re: [PATCH -tip] cpuacct: Make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used. Message-ID: <20090317135938.GV16897@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090317061754.GD3314@in.ibm.com> <49BF42FB.4030103@cn.fujitsu.com> <20090317073649.GH3314@in.ibm.com> <20090317131251.GU16897@balbir.in.ibm.com> <1237296361.7867.16.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1237296361.7867.16.camel@twins> 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 Content-Length: 989 Lines: 25 * Peter Zijlstra [2009-03-17 14:26:01]: > On Tue, 2009-03-17 at 18:42 +0530, Balbir Singh wrote: > > > I'd like to get the patches in -tip and see the results, I would > > recommend using percpu_counter_sum() while reading the data as an > > enhancement to this patch. If user space does not overwhelm with a lot > > of reads, sum would work out better. > > You trust userspace? I'd rather not. > Fair enough.. A badly written application monitor can frequently read this data and cause horrible performance issues. On the other hand large number of CPUs can make the lag even worse. Is it time yet for percpu_counter batch numbers? I've tested this patch and the results were not badly off the mark. -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/