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, M=E5rten Wikstr=F6m 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=20 did you pass through the box? Most likely the "delays" are only seen when=20 the machine is close to capacity (the slow CPU you are using doesnt help). Latency under load and general latency are very different. Differing=20 methods of handling backup conditions may have different goals; the proper= =20 goal is overall stability and NOT packet efficiency. It doesnt matter how=20 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=20 freebsd works up to higher thresholds. You cant evaluate a subsystem with=20 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=20 store-and-forward mode, the default configuration starts in a mode that=20 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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