From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753303Ab1GZH4y (ORCPT ); Tue, 26 Jul 2011 03:56:54 -0400 Received: from TYO200.gate.nec.co.jp ([202.32.8.215]:51847 "EHLO tyo200.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753284Ab1GZH4q (ORCPT ); Tue, 26 Jul 2011 03:56:46 -0400 Message-ID: <4E2E70C3.7050306@ncos.nec.co.jp> Date: Tue, 26 Jul 2011 16:46:11 +0900 From: Keika Kobayashi User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; ja; rv:1.9.1.16) Gecko/20101125 Thunderbird/3.0.11 MIME-Version: 1.0 To: Yong Zhang CC: KOSAKI Motohiro , linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH] proc/softirqs: only show state for online cpus References: <1311599418-1915-1-git-send-email-yong.zhang0@gmail.com> <4E2E507F.7030607@jp.fujitsu.com> <4E2E6102.3060600@jp.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2011/07/26 16:29), Yong Zhang wrote: > On Tue, Jul 26, 2011 at 2:38 PM, KOSAKI Motohiro > wrote: >> (2011/07/26 15:14), Yong Zhang wrote: >>> 2011/7/26 KOSAKI Motohiro : >>>>> Like /proc/interrupts, no need to output data for nobody. >>>>> >>>>> Signed-off-by: Yong Zhang >>>>> Cc: Andrew Morton >>>>> Cc: Keika Kobayashi >>>>> Cc: KOSAKI Motohiro >>>> >>>> If the cpu never be onlined, its statistics always 0. Then, it definitely >>> >>> Yeah, so your screen may contain noise. >> >> One question. Is this big matter? > > Actually it doesn't :) > >> Who see /proc/softirqs and /proc/interrupts directly? (i.e. by 'cat' command). > > By accident I noticed it by accident when running rt kernel. My screen > is full of '0'. > You know my usage is just for testing, maybe the real user is script-like. > >> >> >>>> no value. In the other hand, if the cpu was offlined dynamically, we don't >>>> know the user want to know the cpus's statistics or not. >>> >>> Same to /proc/interrupts :) >>> >>> IMHO, if user want to check the value of offline-cpu, maybe that means >>> he want to check the state of the whole system, /proc/stat should be the >>> right choice. /proc/{softirqs,interrupts} is just for immediate state. >>> >>>> Anyway, it's incompatibility change. >>> >>> Yup, I should have marked the patch with RFC :) >> >> And I should have remarked I don't dislike this patch so strongly, so >> if kobayashi-san who original /proc/softirqs author ack you, I'm going >> to second him. > > Hmmm, so let kobayashi-san decide it. for_each_online_cpu() was in my first patch, like /proc/softirq. But Andrew said -- Probably for_each_possible_cpu() is best - people might want to see how many softirqs happened on a CPU which was recently offlined. -- It makes sense. We would like to collect this information for trouble-shooting. I think for_each_possible_cpu() is better. At that time, I suggested to change from for_each_online_cpu() to for_each_possible_cpu(), in /proc/interrupts. In conclusion, we decided to remain /proc/interrupts. because it had been the way for a long time. >> Offtopic, /proc/interrupt should be protected by get_online_cpus(). >> Otherwise the header (i.e. cpu number) and the actual statistics fields >> can be mismatched likes following. Am I missing something? > > I think you are right. The reader could be preempted by cpu hotplug. > > After searching the whole tree, only s390 take cpu_hotplug.lock, > but its usage is not currect: > > arch/s390/kernel/irq.c: > int show_interrupts(struct seq_file *p, void *v) > { > get_online_cpus(); > ......... > put_online_cpus(); > } > > Because the reader will call show_interrupts nr_irqs times. > So get_online_cpus()/put_online_cpus() should be put upper, > maybe interrupts_open(). How do you think about it? > > Thanks, > Yong > > -- ―――――――――――――――――――――― NEC通信システム 技術管理本部　Linux技術センター 小林　恵果 Mail : kobayashi.kk@ncos.nec.co.jp Tel : 04-7185-6956（内線 : 8-26-35686） ――――――――――――――――――――――