802.1Q vlan performance.
Andrew Thompson
thompsa at freebsd.org
Fri Aug 25 08:41:29 UTC 2006
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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