From owner-freebsd-hackers Mon Mar 19 16:12:28 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from et-gw.etinc.com (et-gw.etinc.com [207.252.1.2]) by hub.freebsd.org (Postfix) with ESMTP id C380837B721 for ; Mon, 19 Mar 2001 16:12:21 -0800 (PST) (envelope-from dennis@etinc.com) Received: from dbsys.etinc.com (dbsys.etinc.com [207.252.1.18]) by et-gw.etinc.com (8.9.3/8.9.3) with ESMTP id TAA03923; Mon, 19 Mar 2001 19:11:29 GMT (envelope-from dennis@etinc.com) Message-Id: <5.0.0.25.0.20010319191529.03fd6a90@mail.etinc.com> X-Sender: dennis@mail.etinc.com X-Mailer: QUALCOMM Windows Eudora Version 5.0 Date: Mon, 19 Mar 2001 19:27:13 -0500 To: =?iso-8859-1?Q?M=E5rten?= =?iso-8859-1?Q?_Wikstr=F6m?= , "'freebsd-hackers@freebsd.org'" From: Dennis Subject: Re: Routing latency In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; format=flowed Content-Transfer-Encoding: quoted-printable Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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