Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 14 Sep 2018 07:06:51 +0200
From:   Steffen Klassert <steffen.klassert@secunet.com>
To:     Florian Westphal <fw@strlen.de>
CC:     David Miller <davem@davemloft.net>, <linux@stwm.de>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <torvalds@linux-foundation.org>, <christophe.gouault@6wind.com>
Subject: Re: Regression: kernel 4.14 an later very slow with many ipsec
 tunnels
Message-ID: <20180914050651.GD23674@gauss3.secunet.de>
References: <20180913135844.3ut6fxgx67t6ndtu@breakpoint.cc>
 <3448099.9yk84El3Sa@stwm.de>
 <20180913163848.ni5xc4gc4d6uusdn@breakpoint.cc>
 <20180913.102305.939671149040995911.davem@davemloft.net>
 <20180913210325.5usfj2rorvuvtyc7@breakpoint.cc>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20180913210325.5usfj2rorvuvtyc7@breakpoint.cc>
User-Agent: Mutt/1.9.4 (2018-02-28)
X-G-Data-MailSecurity-for-Exchange-Sender: 23
X-G-Data-MailSecurity-for-Exchange-Server: cbe3d3f7-b9e3-4256-b890-f24c4306a01c
X-EXCLAIMER-MD-CONFIG: 2c86f778-e09b-4440-8b15-867914633a10
X-G-Data-MailSecurity-for-Exchange-Guid: 5A3DAFA0-D46D-459B-ADC5-B24AE2ECD78E
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Sep 13, 2018 at 11:03:25PM +0200, Florian Westphal wrote:
> David Miller <davem@davemloft.net> wrote:
> > From: Florian Westphal <fw@strlen.de>
> > Date: Thu, 13 Sep 2018 18:38:48 +0200
> > 
> > > Wolfgang Walter <linux@stwm.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.
This might help to balance the hash chains better.

Default hash thresholds are local /32 and remote /32 netmasks, so
all prefixed policies go to the inexact list.

To view the configuration:

ip -s -s x p count