polling(4) rocks!

Yar Tikhiy yar at comp.chem.msu.su
Wed Nov 17 19:00:59 GMT 2004

On Thu, Nov 18, 2004 at 01:52:49AM +0700, Eugene Grosbein wrote:
> On Wed, Nov 17, 2004 at 09:13:51PM +0300, Yar Tikhiy wrote:
> > The router box is a 1.4GHz Celeron PC with an fxp(4) interface split
> > across a dozen of vlans.  There is nothing special about its setup
> > except for ~250 rules loaded into ipfw2.  It is running 4.10-RELEASE.
> > Without polling, it was able to switch full 10Mbytes/sec of traffic
> > (~9kpps), but that took from 50 to 70% CPU time spent in interrupts.
> > With polling on, interrupt time never exceeds 5% and it stays as low
> > as 1-2% on average even when traffic is that high.
> Does polling(4) increase latency? It is very imortant for router
> that handles lots of RTP (VoIP) traffic.
I did no tests of latency, but I guess that polling(4) may even
decrease it in certain cases due to lower overhead of handling
traffic.  Of course, that should be tested in practice, but alas,
we neither run nor use real-time network services here.


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