From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933648Ab2KZRLL (ORCPT ); Mon, 26 Nov 2012 12:11:11 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:47861 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933635Ab2KZRLH (ORCPT ); Mon, 26 Nov 2012 12:11:07 -0500 From: Herton Ronaldo Krzesinski To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Michal Hocko , "Srivatsa S. Bhat" , deepthi@linux.vnet.ibm.com, Thomas Gleixner , Herton Ronaldo Krzesinski Subject: [PATCH 179/270] nohz: Fix idle ticks in cpu summary line of /proc/stat Date: Mon, 26 Nov 2012 14:57:49 -0200 Message-Id: <1353949160-26803-180-git-send-email-herton.krzesinski@canonical.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1353949160-26803-1-git-send-email-herton.krzesinski@canonical.com> References: <1353949160-26803-1-git-send-email-herton.krzesinski@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.5.7u1 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Hocko commit 7386cdbf2f57ea8cff3c9fde93f206e58b9fe13f upstream. 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. [Srivatsa: Rebased to current mainline] Reported-by: Martin Schwidefsky Signed-off-by: Michal Hocko Reviewed-by: Srivatsa S. Bhat Signed-off-by: Srivatsa S. Bhat Link: http://lkml.kernel.org/r/20121010061820.8999.57245.stgit@srivatsabhat.in.ibm.com Cc: deepthi@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner Signed-off-by: Herton Ronaldo Krzesinski --- fs/proc/stat.c | 14 ++++++++++---- 1 file 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); -- 1.7.9.5