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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 12 Dec 2013 13:54:33 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	therbert@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: Cache route in IP tunnels

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 11 Dec 2013 23:37:18 -0800

> 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.

First off I'm glad someone looked into this, I've been meaning to play
with this for a while.

Secondly, Eric's concern is valid but we should keep in mind that IPV6
tunnels do this kind of caching already so if it's undesirable we
should perhaps undo the caching there too.

But honestly I suspect that doing a lookup every packet is more
expensive than false sharing on a cache entry, but I'm happy to be
proven wrong :)
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html