Messages in this thread | | | Date | Tue, 13 Mar 2012 14:02:35 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat |
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On 03/13/2012 01:37 PM, Michal Hocko wrote:
> OK, so the updated version of the patch looks like this. I am sorry but > I had time to only compile test this... > --- > From d12247f14c5f8b00ae97a87442f62e49227a759b Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@suse.cz> > Date: Mon, 12 Mar 2012 13:11:38 +0100 > Subject: [PATCH] nohz: fix idle ticks in cpu summary line of /proc/stat > > 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: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> > Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com> > Signed-off-by: Michal Hocko <mhocko@suse.cz> > --- > 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 121f77c..62bda24 100644 > --- a/fs/proc/stat.c > +++ b/fs/proc/stat.c > @@ -24,10 +24,13 @@ > > 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]; > idle += arch_idle_time(cpu); > } else > @@ -38,10 +41,13 @@ 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);
Yeah, this looks much better..
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Regards, Srivatsa S. Bhat
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