polling(4) rocks!

[James]

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.

If you have a box doing lot of traffic in packets per second, enabling
polling with HZ=2000 +/- will actually *decrease* latency due to far
lower overhead instead of handling all those interrupts/sec.

On a low-to-no traffic box, it's probably not worth it, however use
your own judgement. Either way, the amount of latency polling(4) adds even
in HZ=100 is very low enough (1 ms or less. if using 2000 or so, there is
not much noticeable latency in line of microseconds) to affect most
applications.

-J

-- 
James Jun                                            TowardEX Technologies, Inc.
Technical Lead                       IPv4 and Native IPv6 Colocation, Bandwidth,
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