On Thu 2022-02-03 17:22 -0500, Phil Auld wrote:
> As I said earlier, I don't think you want to call quiet_vmstat()
> unconditionally. And I don't think this will catch the cases you are
> trying to fix. Once the tick is stopped tick_nohz_stop_tick should not be
> getting called again until it's been restarted.
Phil,
Sorry about the delay. If I understand correctly, I see a scenario by which
tick_nohz_stop_tick() can be called on transition/or exit from idle (e.g.
default_idle_call()):
1. The idle/or scheduling-clock was previously
stopped
2. It is considered safe for the scheduling-clock
tick to remain "stopped"/or omitted; no need to
reprogram and enable a periodic tick
(e.g. no queued/or expired pending timer)
...
do_idle
cpuidle_idle_call
{
...
.-- default_idle_call
| arch_cpu_idle
| goto exit_idle
|
| exit_idle:
| __current_set_polling()
|
| }
| tick_nohz_idle_exit()
| {
|
| tick_stopped = ts->tick_stopped
|
| if (tick_stopped)
| tick_nohz_idle_update_tick(ts, now)
| if (tick_nohz_full_cpu(smp_processor_id()))
| __tick_nohz_full_update_tick(ts, now)
| {
| int cpu = smp_processor_id()
|
| if (can_stop_full_tick(cpu, ts))
| tick_nohz_stop_sched_tick(ts, cpu)
| if (tick_nohz_next_event(ts, cpu))
'-- tick_nohz_stop_tick(ts, cpu)
}
}
If I understand correctly, __tick_nohz_full_update_tick() can return with
no changes to the current tick (e.g. expire time == KTIME_MAX), no?
Kind regards,
--
Aaron Tomlin
