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

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Date:	Thu, 28 Apr 2011 17:53:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>,
	Remi Denis-Courmont <remi.denis-courmont@...ia.com>
Subject: Re: [PATCH net-next-2.6] net: dont hold rtnl mutex during netlink
 dump callbacks

Le jeudi 28 avril 2011 à 08:43 -0700, Stephen Hemminger a écrit :
> 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>
> 

Thanks for reviewing Stephen 


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