routing performance w/embedded linux on ppc?

Vladimir A. Gurevich vag at
Thu Nov 27 17:37:34 EST 2003

Brian Kuschak wrote:
> The performance on 4xx is dependent on how much work
> you want to do in the ethernet driver.
> A (nearly) stock kernel will be able to forward 64
> byte packets at around 15,000 pps on 200MHz 405GP.
> The interrupts burn alot of CPU cycles.  If you
> implement a timer-based interrupt mitigation scheme
> using the FIT timer interrupt to clean out the RX and
> TX rings, you will be able to hit about 35K to 40K
> pps.

I definitely agree with Brian's numbers and recommendations :)

Just a couple of comments:

Starting with 2.4.19 or so, I'd recommend looking at NAPI to do
interrupt mitigation instead. Please look at

> On top of that, you can implement
> CONFIG_NET_FASTROUTE in the driver, bypassing most of
> the IP stack.

But, of course, you'll loose IP tables. Also, CONFIG_NET_FASTROUTE won't
help in case you use a DHCP client (or any other app that uses raw
sockets). This might not be that important for a router but be warned!


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