Re: RFC: issues concerning the next NAPI interface

akepner
2007-08-24T15:38:33Z

On Fri, Aug 24, 2007 at 03:59:16PM +0200, Jan-Bernd Themann wrote:
> .......
> 3) On modern systems the incoming packets are processed very fast. Especially
>    on SMP systems when we use multiple queues we process only a few packets
>    per napi poll cycle. So NAPI does not work very well here and the interrupt
>    rate is still high. What we need would be some sort of timer polling mode
>    which will schedule a device after a certain amount of time for high load
>    situations. With high precision timers this could work well. Current
>    usual timers are too slow. A finer granularity would be needed to keep the
> latency down (and queue length moderate).
>

We found the same on ia64-sn systems with tg3 a couple of years
ago. Using simple interrupt coalescing ("don't interrupt until
you've received N packets or M usecs have elapsed") worked
reasonably well in practice. If your h/w supports that (and I'd
guess it does, since it's such a simple thing), you might try
it.

--
Arthur