netdev - Re: CPU usage for IPSec in Linux 2.6.38

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Date:	Tue, 10 Jan 2012 22:34:39 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	nbn@...co.com
Cc:	ipsec-tools-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: CPU usage for IPSec in Linux 2.6.38

From: "Naveen B N (nbn)" <nbn@...co.com>
Date: Wed, 11 Jan 2012 08:20:12 +0530

> Did anybody try creating IPSec Tunnels > 6000 in Linux
> And faced the same problem below.

The problem is that you must situate your rules according to
certain rules otherwise performance will suffer greatly.

You must:

1) Predominantly use fully specified, non-wildcard, rules.

   These go into a special hash table which approaches complexity
   O(1).

2) If you absolutely must have wildcarded rules, only have an
   extremely small number of them.

   These go onto a linked list which is O(N).

There is no reasonable reason to have thousands of wildcarded
rules.

Thousands of fully specified non-wildcard rules are reasonable,
and what we optimize the IPSEC datastructures for.
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