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

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Date:   Fri, 14 Sep 2018 08:01:33 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Florian Westphal <fw@...len.de>
CC:     David Miller <davem@...emloft.net>, <linux@...m.de>,
        <netdev@...r.kernel.org>, <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

On Fri, Sep 14, 2018 at 07:54:37AM +0200, Florian Westphal wrote:
> Steffen Klassert <steffen.klassert@...unet.com> wrote:
> > On Thu, Sep 13, 2018 at 11:03:25PM +0200, Florian Westphal wrote:
> > > 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 :/
> > 
> > The hash threshold can be configured like this:
> > 
> > ip x p set hthresh4 0 0
> > 
> > This sets the hash threshold to local /0 and remote /0 netmasks.
> > With this configuration, all policies should go to the hashtable.
> 
> Yes, but won't they all be hashed to same bucket?
> 
> [ jhash(addr & 0, addr & 0) ] ?

Hm, yes. Maybe something between /0 and /32 makes more sense.