netdev - Re: [RFC net-next PATCH V1 9/9] net: frag remove readers-writer lock (hack)

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Message-ID: <20121125220316.7bbc2287@nehalam.linuxnetplumber.net>
Date:	Sun, 25 Nov 2012 22:03:16 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Thomas Graf <tgraf@...g.ch>, Cong Wang <amwang@...hat.com>,
	"Patrick McHardy" <kaber@...sh.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [RFC net-next PATCH V1 9/9] net: frag remove readers-writer
 lock (hack)

On Fri, 23 Nov 2012 14:08:47 +0100
Jesper Dangaard Brouer <brouer@...hat.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?
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