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

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Date:	Sat, 12 Jan 2008 19:35:58 +0100
From:	Andi Kleen <ak@...e.de>
To:	Benjamin LaHaise <bcrl@...ck.org>
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 Saturday 12 January 2008 18:51:35 Benjamin LaHaise wrote:
> 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().

The call_rcu() could be in free_netdev() couldn't it?

-Andi
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