linux-kernel - Re: [PATCH/RFC] synchronize_rcu(): high latency on idle system

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Message-ID: <20080112175135.GK28570@kvack.org>
Date:	Sat, 12 Jan 2008 12:51:35 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Andi Kleen <ak@...e.de>
Cc:	dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH/RFC] synchronize_rcu(): high latency on idle system

On Sat, Jan 12, 2008 at 03:37:59AM +0100, Andi Kleen wrote:
> > And yes, the 
> > network stack shouldn't call synchronize_rcu() quite so much, but fixing that 
> > is a little more involved.
> 
> ... but the correct solution.

There has to be at least 1 synchronize_rcu() or equivalent in the 
unregister_netdev() path.  I suspect the easiest way to fix it might be to 
use call_rcu() to actually free the network device, as anything else will 
limit performance of single threaded teardown (ie, when an l2tp daemon 
gets terminated via kill -9).  This means an API change that exposes 
rcu for unregister_netdev().

		-ben
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