From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753528AbZB1AOn (ORCPT ); Fri, 27 Feb 2009 19:14:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752878AbZB1AOd (ORCPT ); Fri, 27 Feb 2009 19:14:33 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:32843 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752593AbZB1AOc (ORCPT ); Fri, 27 Feb 2009 19:14:32 -0500 Message-ID: <661fca240cb094bcf4d261ccebab9848.squirrel@webmail-b.css.fujitsu.com> In-Reply-To: References: <20090227140537.390905c4.kamezawa.hiroyu@jp.fujitsu.com> <20090227162928.6225fc80.kamezawa.hiroyu@jp.fujitsu.com> Date: Sat, 28 Feb 2009 09:14:27 +0900 (JST) Subject: Re: [PATCH] change cpuacct usage percpu format v2 From: "KAMEZAWA Hiroyuki" To: "Ken Chen" Cc: "KAMEZAWA Hiroyuki" , "linux-kernel@vger.kernel.org" , "menage@google.com" , "lizf@cn.fujitsu.com" , "balbir@linux.vnet.ibm.com" , mingo@elte.hu, "akpm@linux-foundation.org" User-Agent: SquirrelMail/1.4.16 MIME-Version: 1.0 Content-Type: text/plain;charset=iso-2022-jp Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ken Chen さんは書きました： > On Fri, Feb 27, 2009 at 3:34 PM, KAMEZAWA Hiroyuki > wrote: >> "a lot of" ? I talking about cpu hotplug and reading another file as >> /sys/devices/system/cpu/present every time before reading this file >> gives much much much more overhead ;) > > yes, really a lot. CPU hotplug is an uncommon event. It happens > perhaps once a day? maybe once an hour? > Are you saying the software should have hotplug script and send SIGHUP or some to reload the present map ? > User monitoring process usually reads usage_percpu at fairly high > rate, say once a sec. At each pass it will need to parse N number of > CPU index. The overhead is N_CPU * T, where T is time in second > between cpu hotplug event. Assume T = one day, on a moderate sized > 64-CPU size machine, the overhead is: > > 64 * 86400 : 1, that's like 5.5 million to 1 ratio. To me that is > *high* overhead. > Sounds strange. I can't catch hat you want to say. parsing overhead is == 1. read cpu.usage_perpu. 2. parse the line to number (separated by " ") 3. tie the number to cpu id which is loadead at startup v.s. 1. read cpu.usage_percpu. 2. parse the line to number (sparated by ":" and "\n") 3. record it == Hmm ? no big difference. But okay, if you don't want this, I'll just add warning text to Documentation/cgroup/cpuacct.txt as the user may have to prepare cpu hotplug script if you write flight-recorder like "sar". Thanks, -Kame