netdev - Re: [PATCH net-next-2.6] net: dont hold rtnl mutex during netlink dump callbacks

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Message-Id: <20110502.152733.48516094.davem@davemloft.net>
Date:	Mon, 02 May 2011 15:27:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	eric.dumazet@...il.com, kaber@...sh.net, netdev@...r.kernel.org,
	remi.denis-courmont@...ia.com
Subject: Re: [PATCH net-next-2.6] net: dont hold rtnl mutex during netlink
 dump callbacks

From: Stephen Hemminger <shemminger@...tta.com>
Date: Thu, 28 Apr 2011 08:43:37 -0700

> On Thu, 28 Apr 2011 10:56:07 +0200
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
>> Four years ago, Patrick made a change to hold rtnl mutex during netlink
>> dump callbacks.
>> 
>> I believe it was a wrong move. This slows down concurrent dumps, making
>> good old /proc/net/ files faster than rtnetlink in some situations.
>> 
>> This occurred to me because one "ip link show dev ..." was _very_ slow
>> on a workload adding/removing network devices in background.
>> 
>> All dump callbacks are able to use RCU locking now, so this patch does
>> roughly a revert of commits :
>> 
>> 1c2d670f366 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
>> 6313c1e0992 : [RTNETLINK]: Remove unnecessary locking in dump callbacks
>> 
>> This let writers fight for rtnl mutex and readers going full speed.
>> 
>> It also takes care of phonet : phonet_route_get() is now called from rcu
>> read section. I renamed it to phonet_route_get_rcu()
>> 
>> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>> Cc: Patrick McHardy <kaber@...sh.net>
>> Cc: Remi Denis-Courmont <remi.denis-courmont@...ia.com>
> 
> Acked-by: Stephen Hemminger <shemminger@...tta.com>

Applied, thanks everyone!
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