From owner-freebsd-current@FreeBSD.ORG  Fri Aug 25 08:41:29 2006
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
X-Original-To: freebsd-current@freebsd.org
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id C0A4716A4DD
	for <freebsd-current@freebsd.org>; Fri, 25 Aug 2006 08:41:29 +0000 (UTC)
	(envelope-from thompsa@freebsd.org)
Received: from grunt3.ihug.co.nz (grunt3.ihug.co.nz [203.109.254.43])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 2ACF543D4C
	for <freebsd-current@freebsd.org>; Fri, 25 Aug 2006 08:41:29 +0000 (GMT)
	(envelope-from thompsa@freebsd.org)
Received: from 203-109-251-39.static.bliink.ihug.co.nz (heff.fud.org.nz)
	[203.109.251.39] 
	by grunt3.ihug.co.nz with esmtp (Exim 3.35 #1 (Debian))
	id 1GGXFm-0006Uz-00; Fri, 25 Aug 2006 20:41:26 +1200
Received: by heff.fud.org.nz (Postfix, from userid 1001)
	id 503AF1CC23; Fri, 25 Aug 2006 20:41:26 +1200 (NZST)
Date: Fri, 25 Aug 2006 20:41:26 +1200
From: Andrew Thompson <thompsa@freebsd.org>
To: Ian FREISLICH <if@hetzner.co.za>
Message-ID: <20060825084126.GA80099@heff.fud.org.nz>
Mail-Followup-To: Andrew Thompson <thompsa@freebsd.org>,
	Ian FREISLICH <if@hetzner.co.za>, freebsd-current@freebsd.org
References: <E1GGWGA-000C6D-7d@hetzner.co.za>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <E1GGWGA-000C6D-7d@hetzner.co.za>
User-Agent: Mutt/1.5.11
Cc: freebsd-current@freebsd.org
Subject: Re: 802.1Q vlan performance.
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 25 Aug 2006 08:41:29 -0000

On Fri, Aug 25, 2006 at 09:37:46AM +0200, Ian FREISLICH wrote:
> Hi
> 
> While doing some experimentation and work on ipfw to see where I
> could improve performance for our virtualised firewall I came across
> the following comment in sys/net/if_vlan.c:
> 
>  * The VLAN_ARRAY substitutes the dynamic hash with a static array
>  * with 4096 entries. In theory this can give a boots(sic) in processing,
>  * however on practice it does not. Probably this is because array
>  * is too big to fit into CPU cache.
> 
> Can anyone suggest a good reason not to turn this option on by
> default.  It looks to me like it dramatically improves performance.

Its because of the amount of memory it uses, 16k doesnt sound like much
but its valuable kernel memory. It was discussed a bit here, 
http://lists.freebsd.org/pipermail/freebsd-net/2005-October/008716.html


cheers,
Andrew