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Message-ID: <20070824153703.GN5592@sgi.com>
Date: Fri, 24 Aug 2007 08:37:03 -0700
From: akepner@....com
To: Jan-Bernd Themann <ossthema@...ibm.com>
Cc: netdev <netdev@...r.kernel.org>,
Christoph Raisch <raisch@...ibm.com>,
Jan-Bernd Themann <themann@...ibm.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-ppc <linuxppc-dev@...abs.org>,
Marcus Eder <meder@...ibm.com>,
Thomas Klein <tklein@...ibm.com>,
Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: RFC: issues concerning the next NAPI interface
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
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