Messages in this thread | | | Date | Wed, 16 Feb 2022 14:34:12 +0000 | From | Aaron Tomlin <> | Subject | Re: [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too |
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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
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