On 09/10/2012 04:43 PM, Srivatsa S. Bhat wrote: > From: Michal Hocko <mho...@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 <t...@linutronix.de> > Cc: sta...@vger.kernel.org > Reported-by: Martin Schwidefsky <schwidef...@de.ibm.com> > Reviewed-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com> > Signed-off-by: Michal Hocko <mho...@suse.cz> > [srivatsa.b...@linux.vnet.ibm.com: Rebased to current mainline] > Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@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? >
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); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
