From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [RFC net-next PATCH V1 9/9] net: frag remove readers-writer
 lock (hack)
Date: Sun, 25 Nov 2012 22:03:16 -0800
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	<20121123130847.18764.87682.stgit@dragon>
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Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Florian Westphal <fw@strlen.de>, netdev@vger.kernel.org,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Thomas Graf <tgraf@suug.ch>, Cong Wang <amwang@redhat.com>,
	"Patrick McHardy" <kaber@trash.net>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Herbert Xu <herbert@gondor.hengli.com.au>
To: Jesper Dangaard Brouer <brouer@redhat.com>
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On Fri, 23 Nov 2012 14:08:47 +0100
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> Do NOT APPLY this patch.
> 
> After all the other patches, the rw_lock is now the contention point.

Reader-writer locks are significantly slower than a simple spinlock.
Unless the reader holds the lock for "significant" number of cycles,
a spin lock will be faster. 

Did you try just changing it to a spinlock?