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

From: Ingo Molnar <[email-masked]>
Date: Sun, 26 Apr 2009 13:27:17 +0200

* Paul E. McKenney <[email-masked]> 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