netdev - Re: Regression: kernel 4.14 an later very slow with many ipsec tunnels

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Date:   Thu, 13 Sep 2018 23:03:25 +0200
From:   Florian Westphal <fw@...len.de>
To:     David Miller <davem@...emloft.net>
Cc:     fw@...len.de, linux@...m.de, netdev@...r.kernel.org,
        steffen.klassert@...unet.com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, christophe.gouault@...nd.com
Subject: Re: Regression: kernel 4.14 an later very slow with many ipsec
 tunnels

David Miller <davem@...emloft.net> wrote:
> From: Florian Westphal <fw@...len.de>
> Date: Thu, 13 Sep 2018 18:38:48 +0200
> 
> > Wolfgang Walter <linux@...m.de> wrote:
> >> What I can say is that it depends mainly on number of policy rules and SA.
> > 
> > Thats already a good hint, I guess we're hitting long hash chains in
> > xfrm_policy_lookup_bytype().
> 
> I don't really see how recent changes can influence that.

I don't think there is a recent change that did this.

Walter says < 4.14 is ok, so this is likely related to flow cache removal.

F.e. it looks like all prefixed policies end up in a linked list
(net->xfrm.policy_inexact) and are not even in a hash table.

I am staring at b58555f1767c9f4e330fcf168e4e753d2d9196e0
but can't figure out how to configure that away from the
'no hashing for prefixed policies' default or why we even have
policy_inexact in first place :/

I'll look at this again tomorrow.