On Tue, Apr 21, 2015 at 10:52:18PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 21, 2015 at 06:51:54PM +0200, Frederic Weisbecker wrote:
> > On Tue, Apr 21, 2015 at 05:26:00PM +0200, Peter Zijlstra wrote:
> > > On Tue, Apr 21, 2015 at 02:23:07PM +0200, Frederic Weisbecker wrote:
> > > > +void __init context_tracking_cpu_set(int cpu)
> > > > {
> > > > + static __initdata bool initialized = false;
> > > > + struct task_struct *p, *t;
> > > > +
> > > > + if (!per_cpu(context_tracking.active, cpu)) {
> > > > + per_cpu(context_tracking.active, cpu) = true;
> > > > + static_key_slow_inc(&context_tracking_enabled);
> > > > + }
> > > > +
> > > > + if (initialized)
> > > > + return;
> > > > +
> > > > + set_tsk_thread_flag(&init_task, TIF_NOHZ);
> > > > +
> > > > + /*
> > > > + * There shouldn't be any thread at this early boot stage
> > > > + * but the scheduler is ready to host any. So lets walk
> > > > + * the tasklist just in case. tasklist_lock isn't necessary
> > > > + * either that early but take it for correctness checkers.
> > > > + */
> > > > + read_lock(&tasklist_lock);
> > > > + for_each_process_thread(p, t)
> > > > + set_tsk_thread_flag(t, TIF_NOHZ);
> > >
> > > If there should not be any task, should there not be a WARN_ON_ONCE()
> > > here?
> >
> > Well, it's legal to have a task at that time because sched_init() was
> > called.
> > I just haven't observed any task other than init/0. But future code (or
> > alternate
> > configs than mine) might create a task between sched_init() and
> > tick_init(). And
> > the above code takes care of such a possibility.
>
> So why not do it sooner?
Because I need the tick nohz intialization to be after irq initialization
(init_IRQ()),
which it depends on.
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