Some performance measurements on the FreeBSD network stack

K. Macy kmacy at
Tue Apr 24 15:03:58 UTC 2012

On Tue, Apr 24, 2012 at 4:16 PM, Li, Qing < at> wrote:
> >From previous tests, the difference between flowtable and
>>routing table was small with a single process (about 5% or 50ns
>>in the total packet processing time, if i remember well),
>>but there was a large gain with multiple concurrent processes.
> Yes, that sounds about right when we did the tests a long while ago.
>> Removing flowtable increases the cost in ip_output()
>> (obviously) but also in ether_output() (because the
>> route does not have a lle entry so you need to call
>> arpresolve on each packet).
> Yup.
>> So in revising the route lookup i believe it would be good
>> if we could also get at once most of the info that
>> ether_output() is computing again and again.
> Well, the routing table no longer maintains any lle info, so there
> isn't much to copy out the rtentry at the completion of route
> lookup.
> If I understood you correctly, you do believe there is a lot of value
> in Flowtable caching concept, but you are not suggesting we reverting
> back to having the routing table maintain L2 entries, are you ?

One could try a similar conversion of the L2 table to an rmlock
without copy while lock is held.


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