netdev - Re: [PATCH] xfrm: cache bundle lookup results in flow cache

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Date:	Wed, 17 Mar 2010 16:16:21 +0200
From:	Timo Teräs <timo.teras@....fi>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH] xfrm: cache bundle lookup results in flow cache

Herbert Xu wrote:
> On Mon, Mar 15, 2010 at 02:20:10PM +0200, Timo Teras wrote:
>> Instead of doing O(n) xfrm_find_bundle() call per-packet, cache
>> the previous lookup results in flow cache. The flow cache is
>> updated to be per-netns and more generic.
> 
> This only works well if the traffic doesn't switch bundles much.
> But if that were the case then the number of bundles is likely
> to be small anyway.

The problem is if I have multipoint gre1 and policy that says
"encrypt all gre in transport mode".

Thus for each public address, I get one bundle. But the
xfrm_lookup() is called for each packet because ipgre_tunnel_xmit()
calls ip_route_output_key() on per-packet basis.

For my use-case it makes a huge difference.

> IOW I think if we're doing this then we should go the whole
> distance and directly cache bundles instead of policies in the
> flow cache.

Then we cannot maintain policy use time. But if it's not a
requirement, we could drop the policy from cache.

Also. With this and your recent flowi patch, I'm seeing pmtu
issues. Seems like xfrm_bundle_ok uses the original dst which
resulted in the creation of the bundle. Somehow that dst
does not get updated with pmtu... but the new dst used in
next xfrm_lookup for same target does have proper mtu.
I'm debugging right now why this is happening. Any ideas?

- Timo
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