On Fri, Dec 11 2020 at 23:21, Frederic Weisbecker wrote:
> On Sun, Dec 06, 2020 at 10:12:54PM +0100, Thomas Gleixner wrote:
>> tick_handover_do_timer() which is invoked when a CPU is unplugged has a
>> @@ -407,17 +407,13 @@ EXPORT_SYMBOL_GPL(tick_broadcast_oneshot
>> /*
>> * Transfer the do_timer job away from a dying cpu.
>> *
>> - * Called with interrupts disabled. Not locking required. If
>> + * Called with interrupts disabled. No locking required. If
>> * tick_do_timer_cpu is owned by this cpu, nothing can change it.
>> */
>> void tick_handover_do_timer(void)
>> {
>> - if (tick_do_timer_cpu == smp_processor_id()) {
>> - int cpu = cpumask_first(cpu_online_mask);
>> -
>> - tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
>> - TICK_DO_TIMER_NONE;
>> - }
>> + if (tick_do_timer_cpu == smp_processor_id())
>> + tick_do_timer_cpu = cpumask_first(cpu_online_mask);
>
> I was about to whine that this randomly chosen CPU may be idle and leave
> the timekeeping stale until I realized that stop_machine() is running at that
> time. Might be worth adding a comment about that.
>
> Also why not just setting it to TICK_DO_TIMER_NONE and be done with it?
> Perhaps
> to avoid that all the CPUs to compete and contend on jiffies update after stop
> machine?
No. Because we'd need to add the NONE magic to NOHZ=n kernels which does
not make sense.
Thanks,
tglx
