On Sun, Aug 23, 2015 at 09:01:01AM -0700, Paul E. McKenney wrote:
> The boot CPU is excluded from tick_nohz_full_mask in tick_nohz_init(),
> which is called from tick_init() which is called from start_kernel()
> shortly after rcu_init():
>
> cpu = smp_processor_id();
>
> if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
> pr_warning("NO_HZ: Clearing %d from nohz_full range for
> timekeeping\n", cpu);
> cpumask_clear_cpu(cpu, tick_nohz_full_mask);
> }
>
> This happens after the call to tick_nohz_init_all() that does the
> cpumask_setall() that you called out above.
>
> Or is a recent patch that I missed changing this?
Exactly, this happens right after tick_nohz_full_mask is filled and
makes sure that at least the boot CPU runs as a housekeeper. We
also make sure that it can't become offline later.
Thanks.
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