From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757063AbYJIH3s (ORCPT ); Thu, 9 Oct 2008 03:29:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755626AbYJIH3j (ORCPT ); Thu, 9 Oct 2008 03:29:39 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:62145 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1755487AbYJIH3i (ORCPT ); Thu, 9 Oct 2008 03:29:38 -0400 Message-ID: <48EDB22D.6050908@cn.fujitsu.com> Date: Thu, 09 Oct 2008 15:26:37 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.17 (Windows/20080914) MIME-Version: 1.0 To: KOSAKI Motohiro CC: Andi Kleen , paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, mingo@elte.hu, rjw@sisk.pl, dipankar@in.ibm.com, tglx@linuxtronix.de Subject: Re: [PATCH] rudimentary tracing for Classic RCU References: <20081009065529.GC24560@one.firstfloor.org> <48EDAD55.2000502@cn.fujitsu.com> <20081009161232.DEDC.KOSAKI.MOTOHIRO@jp.fujitsu.com> In-Reply-To: <20081009161232.DEDC.KOSAKI.MOTOHIRO@jp.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org KOSAKI Motohiro wrote: > Hi Lai-san, > >>>> In this case, why not define it as: >>>> static char buf[20*NR_CPUS + 100]; >>> Actually you should near never use NR_CPUS now but always num_possible_cpus() >>> (or even num_online_cpus()) Using NR_CPUS can lead to extreme waste >>> of memory on kernels which are compiled for 4096 CPUs for example. >>> >>> And with num_possible_cpus() kmalloc is needed. >> I thought the default value of NR_CPUS is 32. > > it's pointless. > Almost distribution use _very_ large NR_CPUS (likes 4096). > So, We should concern large NR_CPUS. Thanks. So my advice is to use seq_file. > > >> if NR_CPUS is too large, I think using seq_file is good idea, >> and rcuclassic_trace_mutex is not need too. > > > > >