Subject: Re: [next-20120823] NOHZ: local_softirq_pending 200 on s/r

From: "Paul E. McKenney" <[email-masked]>
Date: Fri, 24 Aug 2012 07:52:47 -0700

On Fri, Aug 24, 2012 at 09:26:08AM +0200, Mike Galbraith wrote:
> On Thu, 2012-08-23 at 12:04 +0200, Sedat Dilek wrote:
> 
> > Jack Winter confirmed to see similiar NOHZ messages also on
> > v3.4.9-rt17 kernel (CPU: Core2Duo when no suspend performed):
> > 
> > [15223.171585] NOHZ: local_softirq_pending 08
> 
> These can be caused by blocking while holding local_softirq_lock.
> 
> Even with per softirq threads, and then (yet more overhead) splitting
> the lock to make sure one softirq type can't block another, _and_ only
> griping if the lock for the pending softirq is _not_ held, seems the
> little bugger can still be triggered very rarely by syn flood induced
> handler bail/raise.  Annoying little gripe :)

Hmmm...  Now that you mention it, if I understand correctly, the
conversion of spinlocks to sleeplocks in -rt would seem to invalidate
this particular diagnostic completely.

So, what am I missing?

							Thanx, Paul