Re: [PATCH RFC] v2 expedited "big hammer" RCU grace periods

Ingo Molnar
2009-04-26T11:29:26Z

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> Second cut of "big hammer" expedited RCU grace periods, but only
> for rcu_bh. This creates another softirq vector, so that entering
> this softirq vector will have forced an rcu_bh quiescent state (as
> noted by Dave Miller). Use smp_call_function() to invoke
> raise_softirq() on all CPUs in order to cause this to happen.
> Track the CPUs that have passed through a quiescent state (or gone
> offline) with a cpumask.

hm, i'm still asking whether doing this would be simpler via a
reschedule vector - which not only is an existing facility but also
forces all RCU domains through a quiescent state - not just bh-RCU
participants.

Triggering a new softirq is in no way simpler that doing an SMP
cross-call - in fact softirqs are a finite resource so using some
other facility would be preferred.

Am i missing something?

Ingo