Re: [PATCH tip/core/rcu 0/2] v2 Add callback-free CPUs

Paul E. McKenney
2012-10-31T07:44:20Z

On Wed, Oct 31, 2012 at 08:25:21AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-10-30 at 20:45 -0700, Paul E. McKenney wrote:
> > This commit therefore adds the ability
> > for selected CPUs ("rcu_nocbs=" boot parameter) to have their
> > callbacks
> > offloaded to kthreads, inspired by Joe Korty's and Jim Houston's JRCU.
> > If the "rcu_nocb_poll" boot parameter is also specified, these
> > kthreads
> > will do polling, removing the need for the offloaded CPUs to do
> > wakeups.
>
> How much pain to make that dynamically configurable?

A fair amount of pain, though I do hope to make it runtime configurable
at some point. Known problems include races between changes in the
nocb configuration, rcu_barrier(), grace-period initialization, and
CPU hotplug. Should be solvable, but want to get the other bugs out of
the way first.

Thanx, Paul