Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads

Thomas Gleixner
2012-06-14T16:20:44Z

On Thu, 14 Jun 2012, Paul E. McKenney wrote:

> On Thu, Jun 14, 2012 at 04:56:29PM +0200, Peter Zijlstra wrote:
> > On Thu, 2012-06-14 at 07:47 -0700, Paul E. McKenney wrote:
> > > RCU callback processing consumes the entire CPU in RCU_BOOST case where
> > > processing runs at real-time priority. This is analogous to RT throttling
> > > in the scheduler.
> >
> > But previously we can in non-preemptible softirq context, why would if
> > behave differently when done from a RT task?
>
> In -rt, yes, but in mainline, ksoftirqd does not run at RT prio, right?
>
> > Also, no its not quite like the throttling, that really idles the cpu
> > even if there's no SCHED_OTHER tasks to run.
>
> Agreed, not -exactly- like throttling, but it has a broadly similar
> goal, namely to prevent a given type of processing from starving
> everything else in the system.
>
> That said, why does throttling idle the CPU even if there is no other
> SCHED_OTHER tasks to run?

For simplicity reasons :)

Thanks,

tglx