netdev - Re: IPsec: Why do pfkey_getspi and xfrm_alloc_userspi call xfrm_find_acq

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Date:	Sun, 22 Aug 2010 00:53:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	christophe.gouault@...nd.com
Cc:	netdev@...r.kernel.org
Subject: Re: IPsec: Why do pfkey_getspi and xfrm_alloc_userspi call
 xfrm_find_acq_byseq?

From: Christophe Gouault <christophe.gouault@...nd.com>
Date: Thu, 19 Aug 2010 14:55:21 +0200

> The call to xfrm_find_acq_byseq() by the pfkey_getspi() and
> xfrm_alloc_userspi() functions is quite costly and proves to entail
> scalability issues when performing thousands of IKE negotiations with
> racoon (from ipsec-tools distribution) or charon (from strongswan
> distribution).
> 
> Removing this call in the kernel drastically accelerates the
> processing and does not seem to entail functional problems.
> 
> For now, I don't see the point of this call. I need to understand its
> purpose, because I'm highly tempted to simply remove it.

First of all, removing a function because you don't understand
why it's there is rarely a good idea :-)

I think the semantics require that we check for existing ACQUIRE
state entries before we allocate an SPI.

The likelyhood of breaking something if you remove the call is very
high.

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