Date: Fri, 25 Aug 2006 20:41:26 +1200 From: Andrew Thompson <thompsa@freebsd.org> To: Ian FREISLICH <if@hetzner.co.za> Cc: freebsd-current@freebsd.org Subject: Re: 802.1Q vlan performance. Message-ID: <20060825084126.GA80099@heff.fud.org.nz> In-Reply-To: <E1GGWGA-000C6D-7d@hetzner.co.za> References: <E1GGWGA-000C6D-7d@hetzner.co.za>
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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
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