From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759106Ab2CMIcx (ORCPT ); Tue, 13 Mar 2012 04:32:53 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:45555 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758953Ab2CMIcs (ORCPT ); Tue, 13 Mar 2012 04:32:48 -0400 Message-ID: <4F5F0623.6080702@linux.vnet.ibm.com> Date: Tue, 13 Mar 2012 14:02:35 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 MIME-Version: 1.0 To: Michal Hocko CC: Martin Schwidefsky , Thomas Gleixner , linux-kernel Subject: Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat References: <20120311182621.41674b39@de.ibm.com> <20120312121726.GA23608@tiehlicka.suse.cz> <20120312101739.26eb373e@de.ibm.com> <4F5E0CC1.6010102@linux.vnet.ibm.com> <20120312153906.GE3994@tiehlicka.suse.cz> <20120312164145.5110ed5c@de.ibm.com> <20120313080748.GA7754@tiehlicka.suse.cz> In-Reply-To: <20120313080748.GA7754@tiehlicka.suse.cz> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 12031308-3864-0000-0000-000001CF5879 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/13/2012 01:37 PM, Michal Hocko wrote: > OK, so the updated version of the patch looks like this. I am sorry but > I had time to only compile test this... > --- > From d12247f14c5f8b00ae97a87442f62e49227a759b Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Mon, 12 Mar 2012 13:11:38 +0100 > Subject: [PATCH] nohz: fix idle ticks in cpu summary line of /proc/stat > > Git commit 09a1d34f8535ecf9 "nohz: Make idle/iowait counter update > conditional" introduced a bug in regard to cpu hotplug. The effect is > that the number of idle ticks in the cpu summary line in /proc/stat is > still counting ticks for offline cpus. > > Reproduction is easy, just start a workload that keeps all cpus busy, > switch off one or more cpus and then watch the idle field in top. > On a dual-core with one cpu 100% busy and one offline cpu you will get > something like this: > > %Cpu(s): 48.7 us, 1.3 sy, 0.0 ni, 50.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st > > The problem is that an offline cpu still has ts->idle_active == 1. > To fix this we should make sure that the cpu is online when calling > get_cpu_idle_time_us and get_cpu_iowait_time_us. > > Cc: Thomas Gleixner > Cc: "Srivatsa S. Bhat" > Reported-by: Martin Schwidefsky > Signed-off-by: Michal Hocko > --- > fs/proc/stat.c | 14 ++++++++++---- > 1 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/fs/proc/stat.c b/fs/proc/stat.c > index 121f77c..62bda24 100644 > --- a/fs/proc/stat.c > +++ b/fs/proc/stat.c > @@ -24,10 +24,13 @@ > > static u64 get_idle_time(int cpu) > { > - u64 idle, idle_time = get_cpu_idle_time_us(cpu, NULL); > + u64 idle, idle_time = -1ULL; > + > + if (cpu_online(cpu)) > + idle_time = get_cpu_idle_time_us(cpu, NULL); > > if (idle_time == -1ULL) { > - /* !NO_HZ so we can rely on cpustat.idle */ > + /* !NO_HZ or cpu offline so we can rely on cpustat.idle */ > idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE]; > idle += arch_idle_time(cpu); > } else > @@ -38,10 +41,13 @@ static u64 get_idle_time(int cpu) > > static u64 get_iowait_time(int cpu) > { > - u64 iowait, iowait_time = get_cpu_iowait_time_us(cpu, NULL); > + u64 iowait, iowait_time = -1ULL; > + > + if (cpu_online(cpu)) > + iowait_time = get_cpu_iowait_time_us(cpu, NULL); > > if (iowait_time == -1ULL) > - /* !NO_HZ so we can rely on cpustat.iowait */ > + /* !NO_HZ or cpu offline so we can rely on cpustat.iowait */ > iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT]; > else > iowait = usecs_to_cputime64(iowait_time); Yeah, this looks much better.. Reviewed-by: Srivatsa S. Bhat Regards, Srivatsa S. Bhat