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

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Message-ID: <1345793168.4331.64.camel@marge.simpson.net>
Date:	Fri, 24 Aug 2012 09:26:08 +0200
From:	Mike Galbraith <efault@....de>
To:	sedat.dilek@...il.com
Cc:	Paul McKenney <paul.mckenney@...aro.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	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 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 :)

-Mike

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