netdev - Re: [PATCH] net: Cache route in IP tunnels

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Date:	Wed, 11 Dec 2013 23:37:18 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] net: Cache route in IP tunnels

On Wed, 2013-12-11 at 22:17 -0800, Tom Herbert wrote:
> Avoid doing a route lookup on every packet being tunneled.
> 
> In ip_tunnel.c cache the route returned from ip_route_output if
> the tunnel is "connected", that is all the routing parameters are
> taken from tunnel parms for a packet. Specifically, not NBMA tunnel
> and tos is from tunnel parms (not inner packet).
> 
> Signed-off-by: Tom Herbert <therbert@...gle.com>
> ---

Replacing per cpu dst (nh_pcpu_rth_output) with a single shared dst is
not going to be better on SMP.

Do you have any performance data using multiqueue NIC, with say 32 cpus
and 32 TX queues ?

I suspect a high false sharing on dst refcount.

Thanks


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