netdev - Re: [RFC PATCH] netfilter: conntrack: cache route for forwarded connections

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Message-ID: <1417484203.4442.19.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 01 Dec 2014 17:36:43 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netfilter-devel@...r.kernel.org, brouer@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] netfilter: conntrack: cache route for forwarded
 connections

On Tue, 2014-12-02 at 01:28 +0100, Florian Westphal wrote:
> ... to avoid per-packet FIB lookup if possible.
> 
> The cached dst is re-used provided the input interface
> is the same as that of the previous packet in the same direction.
> 
> If not, the cached dst is invalidated.
> 
> This should speed up forwarding when conntrack is already in use
> anyway, especially when using reverse path filtering -- active RPF
> enforces two FIB lookups for each packet.
> 
> Before the routing cache removal this didn't matter since RPF
> was performed only when route cache didn't yield a result; but without
> route cache it comes at high price.
> 
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---

Seems a good idea (but you might need some IPv6 care, as ( dst =
dst_check(dst, 0); ) seems to handle IPv4 only)

Another idea would be to re-use TCP ehash so that regular IP early demux
can be used, with a single lookup for both local and forwarded sessions.

(That would probably require a bit more memory, as you would need to
insert into TCP ehash some kind of 'tiny sockets' )

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