On Thu, Apr 02, 2015 at 08:08:03PM +0200, Oleg Nesterov wrote:
> On 04/02, Frederic Weisbecker wrote:
> >
> > +void context_tracking_cpu_set(int cpu)
> > {
> > - clear_tsk_thread_flag(prev, TIF_NOHZ);
> > - set_tsk_thread_flag(next, TIF_NOHZ);
> > + static bool initialized = false;
> > + struct task_struct *p, *t;
> > + unsigned long flags;
> > +
> > + 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_irqsave(&tasklist_lock, flags);
> > + for_each_process_thread(p, t)
> > + set_tsk_thread_flag(t, TIF_NOHZ);
> > + read_unlock_irqrestore(&tasklist_lock, flags);
> > +
> > + initialized = true;
> > }
>
> Agreed, but _irqsave is not needed. read_lock(tasklist) should work
> just fine.
Indeed, that was just in case we get more callers but then if it happens,
it's their responsibility to fix the callee. So I'll just change that.
>
> Any reason 3/3 comes as a separate change? I won't argue, just curious.
Nope, I should fold them indeed.
Thanks.
>
> Oleg.
>
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