Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks()

Paul E. McKenney
2014-08-09T16:16:26Z

On Sat, Aug 09, 2014 at 08:44:39AM -0400, Steven Rostedt wrote:
> On Sat, 9 Aug 2014 08:15:14 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> > As for idle tasks, I'm not sure about those, I think that we should say
> > NO to anything that would require waking idle CPUs, push the pain to
> > ftrace/kprobes, we should _not_ be waking idle cpus.
>
> I agree, but I haven't had a chance to review the patch set (will
> probably do that on Monday, just got back from vacation last week and
> was inundated by other things).

Let me get v5 out first. I expect to have it out by end of Monday.

> Does the idle waking happen only when
> there's something queued in the call_rcu_tasks()? It should definitely
> not be waking all the time. That's just wrong.
>
> But if it only wakes when something is queued, it wouldn't be burdening
> anything, unless it is needed.

Indeed, idle waking only happens when there is an RCU-tasks grace period
in progress. No RCU-tasks grace period, no RCU-tasks idle waking.

Thanx, Paul