Messages in this thread Patch in this message | | | Date | Tue, 20 Aug 2013 20:15:00 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH RESEND 0/4] nohz: Fix racy sleeptime stats |
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While at it.
I do not also understand the cpu_online() checks in fs/proc/stat.c.
OK, I agree, if cpu is offline it should not participate in cpu summary. But if it goes offline, why it should switch from ->iowait_sleeptime + cpustat[CPUTIME_IDLE] as it seen by /proc/stat?
This can be another source of "idle goes backward", no?
IOW. Ignoring the other problems we have, perhaps something like below makes sense?
Oleg.
--- x/fs/proc/stat.c +++ x/fs/proc/stat.c @@ -45,10 +45,9 @@ static cputime64_t get_iowait_time(int c static u64 get_idle_time(int cpu) { - u64 idle, idle_time = -1ULL; + u64 idle, idle_time; - if (cpu_online(cpu)) - idle_time = get_cpu_idle_time_us(cpu, NULL); + idle_time = get_cpu_idle_time_us(cpu, NULL); if (idle_time == -1ULL) /* !NO_HZ or cpu offline so we can rely on cpustat.idle */ @@ -61,10 +60,9 @@ static u64 get_idle_time(int cpu) static u64 get_iowait_time(int cpu) { - u64 iowait, iowait_time = -1ULL; + u64 iowait, iowait_time; - if (cpu_online(cpu)) - iowait_time = get_cpu_iowait_time_us(cpu, NULL); + iowait_time = get_cpu_iowait_time_us(cpu, NULL); if (iowait_time == -1ULL) /* !NO_HZ or cpu offline so we can rely on cpustat.iowait */ --- x/kernel/time/tick-sched.c +++ x/kernel/time/tick-sched.c @@ -477,7 +477,7 @@ u64 get_cpu_idle_time_us(int cpu, u64 *l update_ts_time_stats(cpu, ts, now, last_update_time); idle = ts->idle_sleeptime; } else { - if (ts->idle_active && !nr_iowait_cpu(cpu)) { + if (ts->idle_active && cpu_online(cpu) && !nr_iowait_cpu(cpu)) { ktime_t delta = ktime_sub(now, ts->idle_entrytime); idle = ktime_add(ts->idle_sleeptime, delta); @@ -518,7 +518,7 @@ u64 get_cpu_iowait_time_us(int cpu, u64 update_ts_time_stats(cpu, ts, now, last_update_time); iowait = ts->iowait_sleeptime; } else { - if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { + if (ts->idle_active && cpu_online(cpu) && nr_iowait_cpu(cpu)) { ktime_t delta = ktime_sub(now, ts->idle_entrytime); iowait = ktime_add(ts->iowait_sleeptime, delta);
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