Messages in this thread Patch in this message | | | Date | Fri, 30 Mar 2012 12:23:08 +0200 | From | Martin Schwidefsky <> | Subject | Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat |
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Hi Thomas,
On Thu, 29 Mar 2012 12:42:22 +0200 (CEST) Thomas Gleixner <tglx@linutronix.de> wrote:
> On Tue, 13 Mar 2012, 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> > > Martin, does that solve the problem for you ?
Yes, the patch does solve the immediate problem. I just tested if again on x86 and s390, works fine. I would like to have another change though. The idle_sleep calculation in the scheduler is fine for x86 but for s390 the arch_idle_time delivers a much better precision. A patch would look like this: -- Subject: [PATCH] use arch_idle_time for idle and iowait times if available
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Git commit a25cac5198d4ff28 "proc: Consider NO_HZ when printing idle and iowait times" changes the code for /proc/stat to use get_cpu_idle_time_us and get_cpu_iowait_time_us if the system is running with nohz enabled. For architectures which define arch_idle_time (currently s390 only) this is a change for the worse. The result of arch_idle_time is supposed to be the exact sleep time of the target cpu and should be used instead of the value kept by the scheduler.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> --- fs/proc/stat.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-)
--- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -18,9 +18,30 @@ #ifndef arch_irq_stat #define arch_irq_stat() 0 #endif -#ifndef arch_idle_time -#define arch_idle_time(cpu) 0 -#endif + +#ifdef arch_idle_time + +static cputime64_t get_idle_time(int cpu) +{ + cputime64_t idle; + + idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE]; + if (cpu_online(cpu) && !nr_iowait_cpu(cpu)) + idle += arch_idle_time(cpu); + return idle; +} + +static cputime64_t get_iowait_time(int cpu) +{ + cputime64_t iowait; + + iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT]; + if (cpu_online(cpu) && nr_iowait_cpu(cpu)) + iowait += arch_idle_time(cpu); + return iowait; +} + +#else static u64 get_idle_time(int cpu) { @@ -29,11 +50,10 @@ static u64 get_idle_time(int cpu) if (cpu_online(cpu)) idle_time = get_cpu_idle_time_us(cpu, NULL); - if (idle_time == -1ULL) { + if (idle_time == -1ULL) /* !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 + else idle = usecs_to_cputime64(idle_time); return idle; @@ -55,6 +75,8 @@ static u64 get_iowait_time(int cpu) return iowait; } +#endif + static int show_stat(struct seq_file *p, void *v) { int i, j; -- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
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