From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757452Ab2IJLNl (ORCPT ); Mon, 10 Sep 2012 07:13:41 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:59212 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757174Ab2IJLNh (ORCPT ); Mon, 10 Sep 2012 07:13:37 -0400 From: "Srivatsa S. Bhat" Subject: [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat To: tglx@linutronix.de, mhocko@suse.cz Cc: schwidefsky@de.ibm.com, deepthi@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com Date: Mon, 10 Sep 2012 16:43:09 +0530 Message-ID: <20120910111157.3940.68948.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit x-cbid: 12091011-3864-0000-0000-0000048F4ECE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? [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);