3.2-stable review patch. If anyone has any objections, please let me know.
------------------ From: Michal Hocko <[email protected]> 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 <[email protected]> Signed-off-by: Michal Hocko <[email protected]> Reviewed-by: Srivatsa S. Bhat <[email protected]> Signed-off-by: Srivatsa S. Bhat <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Cc: [email protected] Signed-off-by: Thomas Gleixner <[email protected]> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <[email protected]> --- fs/proc/stat.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -24,11 +24,14 @@ static cputime64_t get_idle_time(int cpu) { - u64 idle_time = get_cpu_idle_time_us(cpu, NULL); + u64 idle_time = -1ULL; cputime64_t idle; + 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 = kstat_cpu(cpu).cpustat.idle; idle = cputime64_add(idle, arch_idle_time(cpu)); } else @@ -39,11 +42,14 @@ static cputime64_t get_idle_time(int cpu static cputime64_t get_iowait_time(int cpu) { - u64 iowait_time = get_cpu_iowait_time_us(cpu, NULL); + u64 iowait_time = -1ULL; cputime64_t iowait; + 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 = kstat_cpu(cpu).cpustat.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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
