Heiko Carstens c952654e1a tick-sched: Fix idle and iowait sleeptime accounting vs CPU hotplug ... commit 71fee48fb772ac4f6cfa63dbebc5629de8b4cc09 upstream. When offlining and onlining CPUs the overall reported idle and iowait times as reported by /proc/stat jump backward and forward: cpu 132 0 176 225249 47 6 6 21 0 0 cpu0 80 0 115 112575 33 3 4 18 0 0 cpu1 52 0 60 112673 13 3 1 2 0 0 cpu 133 0 177 226681 47 6 6 21 0 0 cpu0 80 0 116 113387 33 3 4 18 0 0 cpu 133 0 178 114431 33 6 6 21 0 0 <---- jump backward cpu0 80 0 116 114247 33 3 4 18 0 0 cpu1 52 0 61 183 0 3 1 2 0 0 <---- idle + iowait start with 0 cpu 133 0 178 228956 47 6 6 21 0 0 <---- jump forward cpu0 81 0 117 114929 33 3 4 18 0 0 Reason for this is that get_idle_time() in fs/proc/stat.c has different sources for both values depending on if a CPU is online or offline: - if a CPU is online the values may be taken from its per cpu tick_cpu_sched structure - if a CPU is offline the values are taken from its per cpu cpustat structure The problem is that the per cpu tick_cpu_sched structure is set to zero on CPU offline. See tick_cancel_sched_timer() in kernel/time/tick-sched.c. Therefore when a CPU is brought offline and online afterwards both its idle and iowait sleeptime will be zero, causing a jump backward in total system idle and iowait sleeptime. In a similar way if a CPU is then brought offline again the total idle and iowait sleeptimes will jump forward. It looks like this behavior was introduced with commit 4b0c0f294f ("tick: Cleanup NOHZ per cpu data on cpu down"). This was only noticed now on s390, since we switched to generic idle time reporting with commit be76ea614460 ("s390/idle: remove arch_cpu_idle_time() and corresponding code"). Fix this by preserving the values of idle_sleeptime and iowait_sleeptime members of the per-cpu tick_sched structure on CPU hotplug. Fixes: 4b0c0f294f ("tick: Cleanup NOHZ per cpu data on cpu down") Reported-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20240115163555.1004144-1-hca@linux.ibm.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2024-01-25 15:27:39 -08:00
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alarmtimer.c
clockevents.c
clocksource-wdtest.c
clocksource.c
hrtimer.c	hrtimers: Push pending hrtimers away from outgoing CPU earlier	2023-12-13 18:39:03 +01:00
itimer.c
jiffies.c
Kconfig
Makefile
namespace.c
ntp.c
ntp_internal.h
posix-clock.c
posix-cpu-timers.c	posix-cpu-timers: Implement the missing timer_wait_running callback	2023-05-11 23:03:00 +09:00
posix-stubs.c
posix-timers.c	posix-timers: Prevent RT livelock in itimer_delete()	2023-07-19 16:20:59 +02:00
posix-timers.h
sched_clock.c
test_udelay.c	time/debug: Fix memory leak with using debugfs_lookup()	2023-03-10 09:33:52 +01:00
tick-broadcast-hrtimer.c
tick-broadcast.c	tick/broadcast: Make broadcast device replacement work correctly	2023-05-24 17:32:31 +01:00
tick-common.c	tick/common: Align tick period during sched_timer setup	2023-06-28 11:12:18 +02:00
tick-internal.h
tick-legacy.c
tick-oneshot.c
tick-sched.c	tick-sched: Fix idle and iowait sleeptime accounting vs CPU hotplug	2024-01-25 15:27:39 -08:00
tick-sched.h
time.c
time_test.c
timeconst.bc
timeconv.c
timecounter.c
timekeeping.c	timekeeping: Fix references to nonexistent ktime_get_fast_ns()	2023-05-11 23:03:35 +09:00
timekeeping.h
timekeeping_debug.c
timekeeping_internal.h
timer.c
timer_list.c
vsyscall.c