On Tue, 15 Dec 2020 15:23:39 +0100 (CET) Anna-Maria Behnsen <anna-ma...@linutronix.de> wrote:
> > > + /* > > > + * Remove CPU from nohz.idle_cpus_mask to prevent participating in > > > + * load balancing when not active > > > + */ > > > + nohz_balance_exit_idle(rq); > > > + > > > set_cpu_active(cpu, false); > > > /* > > > * We've cleared cpu_active_mask, wait for all preempt-disabled and RCU > > > > > > > OK, so we must clear the state before !active, because getting an > > interrupt/softirq after would trigger the badness. And we're guaranteed > > nothing blocks between them to re-set it. > > As far as I understood, it is not a problem whether the delete is before or > after !active. When it is deleted after, the remote CPU will return in > kick_ilb() because cpu is not idle, because it is running the hotplug > thread. I was thinking that disabling it after may also cause some badness. Even if it does not, I think there's no harm in clearing it just before setting cpu active to false. And I find that the safer option. -- Steve
