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

Paul E. McKenney
2012-06-14T15:46:13Z

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?

Thanx, Paul