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| author | Frederic Weisbecker <frederic@kernel.org> | 2024-02-25 23:55:06 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2024-02-26 11:37:32 +0100 |
| commit | 3f69d04e146c6e14ccdd4e7b37d93f789229202a (patch) | |
| tree | a4e0633e44bc1c2612378638f4f92f4fe3beee9a /kernel/time/tick-common.c | |
| parent | 7988e5ae2be70b110db9d4b8ec163bd42e67d3be (diff) | |
| download | linux-3f69d04e146c6e14ccdd4e7b37d93f789229202a.tar.gz | |
tick: Shut down low-res tick from dying CPU
The timekeeping duty is handed over from the outgoing CPU within stop
machine. This works well if CONFIG_NO_HZ_COMMON=n or the tick is in
high-res mode. However in low-res dynticks mode, the tick isn't
cancelled until the clockevent is shut down, which can happen later. The
tick may therefore fire again once IRQs are re-enabled on stop machine
and until IRQs are disabled for good upon the last call to idle.
That's so many opportunities for a timekeeper to go idle and the
outgoing CPU to take over that duty. This is why
tick_nohz_idle_stop_tick() is called one last time on idle if the CPU
is seen offline: so that the timekeeping duty is handed over again in
case the CPU has re-taken the duty.
This means there are two timekeeping handovers on CPU down hotplug with
different undocumented constraints and purposes:
1) A handover on stop machine for !dynticks || highres. All online CPUs
are guaranteed to be non-idle and the timekeeping duty can be safely
handed-over. The hrtimer tick is cancelled so it is guaranteed that in
dynticks mode the outgoing CPU won't take again the duty.
2) A handover on last idle call for dynticks && lowres. Setting the
duty to TICK_DO_TIMER_NONE makes sure that a CPU will take over the
timekeeping.
Prepare for consolidating the handover to a single place (the first one)
with shutting down the low-res tick as well from
tick_cancel_sched_timer() as well. This will simplify the handover and
unify the tick cancellation between high-res and low-res.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-15-frederic@kernel.org
Diffstat (limited to 'kernel/time/tick-common.c')
| -rw-r--r-- | kernel/time/tick-common.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 522414089c0d79..9cd09eea06d6e3 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -410,7 +410,8 @@ int tick_cpu_dying(unsigned int dying_cpu) if (tick_do_timer_cpu == dying_cpu) tick_do_timer_cpu = cpumask_first(cpu_online_mask); - tick_cancel_sched_timer(dying_cpu); + /* Make sure the CPU won't try to retake the timekeeping duty */ + tick_sched_timer_dying(dying_cpu); /* Remove CPU from timer broadcasting */ tick_offline_cpu(dying_cpu); |