Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp]

Sepherosa Ziehau sepherosa at
Tue Jul 1 03:34:53 UTC 2008

On 7/1/08, Paul <paul at> wrote:
> I have been unable to even come close to livelocking the machine with the em
> driver interrupt moderation.

Yeah, system will not be livelocked.  But even setting its imtimer to
4000, the overall system response is still worse than using polling
@4000 with a 9402PT.

>  So that to me throws polling out the window.  I tried 8000hz with polling

I don't believe high polling rate will improve forwarding performance.
 I used to set polling rate to 2000hz, burst max to 750 and each burst
to 60.

> modified to allow 10000 burst and it makes no difference
>  in the amount of pps I can jam through.. It' seems to be limited by the
> routing path in the kernel more than anything else.
>  If a driver/hardware didn't support interrupt mitigation then it would
> definitely lock the machine.

So polling(4) still has its place.

Best Regards,

Live Free or Die

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