Messages in this thread | | | Date | Tue, 21 Apr 2015 22:52:18 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] context_tracking: Inherit TIF_NOHZ through forks instead of context switches |
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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?
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