From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754066Ab2IYSur (ORCPT ); Tue, 25 Sep 2012 14:50:47 -0400 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:48156 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753244Ab2IYSuq (ORCPT ); Tue, 25 Sep 2012 14:50:46 -0400 Message-ID: <5061FCDD.6050406@linux.vnet.ibm.com> Date: Wed, 26 Sep 2012 00:20:05 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Thomas Gleixner CC: Ingo Molnar , mhocko@suse.cz, schwidefsky@de.ibm.com, deepthi@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, "Srivatsa S. Bhat" Subject: Re: [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat References: <20120910111157.3940.68948.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20120910111157.3940.68948.stgit@srivatsabhat.in.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12092518-5564-0000-0000-0000049D614B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/10/2012 04:43 PM, Srivatsa S. Bhat wrote: > From: Michal Hocko > > 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: stable@vger.kernel.org > Reported-by: Martin Schwidefsky > Reviewed-by: Srivatsa S. Bhat > Signed-off-by: Michal Hocko > [srivatsa.bhat@linux.vnet.ibm.com: Rebased to current mainline] > Signed-off-by: Srivatsa S. Bhat > --- > > Hi Thomas, > > This is a resend of the patch posted by Michal at [1]. Martin had explained > the importance of this patch for fixing the bug for x86 case in [2]. (The s390 > fix is already upstream, commit id cb85a6ed67e9). Could you kindly consider > taking this fix? > Hi Thomas, Any thoughts on this? Regards, Srivatsa S. Bhat > [1]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1266457 > [2]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1276336 > > 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 64c3b31..e296572 100644 > --- a/fs/proc/stat.c > +++ b/fs/proc/stat.c > @@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int cpu) > > 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]; > else > idle = usecs_to_cputime64(idle_time); > @@ -58,10 +61,13 @@ 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); >