linux-kernel - Re: [next-20120823] NOHZ: local_softirq

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Message-ID: <20120824145247.GB2472@linux.vnet.ibm.com>
Date:	Fri, 24 Aug 2012 07:52:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
Cc:	sedat.dilek@...il.com, Paul McKenney <paul.mckenney@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-next <linux-next@...r.kernel.org>
Subject: Re: [next-20120823] NOHZ: local_softirq_pending 200 on s/r

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

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