netdev - Re: [PATCH net-next-2.6] net: avoid synchronize_rcu() in dev_deactivate

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Message-Id: <20110522.210255.1260763671419618526.davem@davemloft.net>
Date:	Sun, 22 May 2011 21:02:55 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	greearb@...delatech.com, netdev@...r.kernel.org, kaber@...sh.net
Subject: Re: [PATCH net-next-2.6] net: avoid synchronize_rcu() in
 dev_deactivate_many

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 20 May 2011 11:42:09 +0200

> dev_deactivate_many() issues one synchronize_rcu() call after qdiscs set
> to noop_qdisc.
> 
> This call is here to make sure they are no outstanding qdisc-less
> dev_queue_xmit calls before returning to caller.
> 
> But in dismantle phase, we dont have to wait, because we wont activate
> again the device, and we are going to wait one rcu grace period later in
> rollback_registered_many().
> 
> After this patch, device dismantle uses one synchronize_net() and one
> rcu_barrier() call only, so we have a ~30% speedup and a smaller RTNL
> latency.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Patrick McHardy <kaber@...sh.net>,
> CC: Ben Greear <greearb@...delatech.com>

Applied.
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