Date: Wed, 17 Nov 2004 16:03:21 -0500 From: James <haesu@towardex.com> To: Eugene Grosbein <eugen@grosbein.pp.ru> Cc: net@freebsd.org Subject: Re: polling(4) rocks! Message-ID: <20041117210321.GA73977@scylla.towardex.com> In-Reply-To: <20041117185248.GA1394@grosbein.pp.ru> References: <20041117181351.GA48071@comp.chem.msu.su> <20041117185248.GA1394@grosbein.pp.ru>
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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, james@towardex.com and Web Hosting Services in the Metro Boston area cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
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