This is a note to let you know that I've just added the patch titled nohz: Fix idle ticks in cpu summary line of /proc/stat
to the 3.6-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat.patch and it can be found in the queue-3.6 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@vger.kernel.org> know about it. >From 7386cdbf2f57ea8cff3c9fde93f206e58b9fe13f Mon Sep 17 00:00:00 2001 From: Michal Hocko <mho...@suse.cz> Date: Wed, 10 Oct 2012 11:51:09 +0530 Subject: nohz: Fix idle ticks in cpu summary line of /proc/stat From: Michal Hocko <mho...@suse.cz> 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 <schwidef...@de.ibm.com> Signed-off-by: Michal Hocko <mho...@suse.cz> Reviewed-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com> Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20121010061820.8999.57245.st...@srivatsabhat.in.ibm.com Cc: deep...@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner <t...@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- fs/proc/stat.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int c 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); Patches currently in stable-queue which might be from mho...@suse.cz are queue-3.6/nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html