Date: Mon, 19 Mar 2001 19:27:13 -0500 From: Dennis <dennis@etinc.com> To: =?iso-8859-1?Q?M=E5rten?= =?iso-8859-1?Q?_Wikstr=F6m?= <Marten.Wikstrom@framfab.se>, "'freebsd-hackers@freebsd.org'" <freebsd-hackers@FreeBSD.ORG> Subject: Re: Routing latency Message-ID: <5.0.0.25.0.20010319191529.03fd6a90@mail.etinc.com> In-Reply-To: <E6D22E487D45D411931B00508BCF93E75C0330@storeg001.framfab.s e>
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At 09:22 AM 03/19/2001, 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? Were you loading the interface, or just passing nominal streams? What pps did you pass through the box? Most likely the "delays" are only seen when the machine is close to capacity (the slow CPU you are using doesnt help). Latency under load and general latency are very different. Differing methods of handling backup conditions may have different goals; the proper goal is overall stability and NOT packet efficiency. It doesnt matter how fast a man runs if he doesnt finish the race. The problem with LINUX is that it works to a point and then chokes, while freebsd works up to higher thresholds. You cant evaluate a subsystem with one somewhat bogus test, without looking at the system as a whole. If you are using the dc driver, make certain it is operating in store-and-forward mode, the default configuration starts in a mode that only works on 10mb/s connections. dennis To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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