The patch titled Subject: nohz: fix idle ticks in cpu summary line of /proc/stat has been removed from the -mm tree. Its filename was nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Michal Hocko <mhocko@xxxxxxx> Subject: nohz: fix idle ticks in cpu summary line of /proc/stat 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.bhat@xxxxxxxxxxxxxxxxxx: rebased to current mainline] Reported-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxx> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/proc/stat.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff -puN fs/proc/stat.c~nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat fs/proc/stat.c --- a/fs/proc/stat.c~nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat +++ a/fs/proc/stat.c @@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int c 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); _ Patches currently in -mm which might be from mhocko@xxxxxxx are linux-next.patch mm-memblock-reduce-overhead-in-binary-search.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html