Messages in this thread Patch in this message | | | From | "Srivatsa S. Bhat" <> | Subject | [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat | Date | Mon, 10 Sep 2012 16:43:09 +0530 |
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From: Michal Hocko <mhocko@suse.cz>
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 <tglx@linutronix.de> Cc: stable@vger.kernel.org Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Signed-off-by: Michal Hocko <mhocko@suse.cz> [srivatsa.bhat@linux.vnet.ibm.com: Rebased to current mainline] Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
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);
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