Date: Mon, 19 Mar 2001 20:32:25 +0100 From: Thierry Herbelot <thierry@herbelot.com> To: =?iso-8859-1?Q?M=E5rten=20Wikstr=F6m?= <Marten.Wikstrom@framfab.se> Cc: "'freebsd-hackers@freebsd.org'" <freebsd-hackers@FreeBSD.ORG> Subject: Re: Routing latency Message-ID: <3AB65EC9.4D969490@herbelot.com> References: <E6D22E487D45D411931B00508BCF93E75C0330@storeg001.framfab.se>
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Hello, the FreeBSD TCP/IP stack uses the "system tick timer" for some delay (maybe only for TCP). you may want to use a HZ=1000 option (see the LINT config file) in a recompiled kernel and see if things go better. (moreover, the dc(4) driver which is used for your NIC has some interesting performance improvements in the forthcoming 4.3-Release) TfH Mårten Wikström wrote: > > I've performed a routing test between a FreeBSD box and a Linux box. I > measured the latency and the result was not what I had expected. Both > systems had the peak at 100 us (microseconds), but whereas the Linux box had > _no_ packet over 200 us, the FreeBSD box delayed some packets up to 2 ms! > Looking at the time series, it seems that the packets are delayed at regular > intervals, about every second. My guess is that some timer interrupt > triggers every second and steals too much cpu. So my question is, how can I > decrease this routing delay? > > Test info: > I used two identical boxes, each equipped with a Pentium Pro 200Mhz and 64Mb > mem. RedHat 7.0 with 2.4 kernel in one and FreeBSD 4.2-RELEASE in the other. > I used two DEC 100Mbit ethernet cards (21140 I think). > I measured the latency with a SmartBits instrument. Fastforwarding was > disabled. Three UDP streams was sent from the SmartBits to one of the > ethernet cards in the box, which routed the streams to the other interface, > which in turn was connected back to the SmartBits. > I had not made any changes to the standard kernel configuration. No other > processes was running in the background, apart from those necessary to > perform the test. The ARP table was set statically, so no ARP traffic would > disturb. > > I would at least want to know what is causing the extra delays. > > /Mårten > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message -- Thierry Herbelot To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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