----- Original Message ----- From: "David G. Andersen" <dga@lcs.mit.edu> To: "todd glassey" <todd.glassey@worldnet.att.net> Cc: "Jared Mauch" <jared@puck.Nether.net>; "Martin Hannigan" <hannigan@fugawi.net>; "Wojtek Zlobicki" <wojtekz@idirect.com>; "Alan Sato" <asato@altrio.net>; <nanog@trapdoor.merit.edu> Sent: Wednesday, June 26, 2002 6:30 AM Subject: Re: Testing Bandwidth performance
On Wed, Jun 26, 2002 at 06:18:00AM -0700, todd glassey mooed:
I have never been referred to as bovine before. I usually describe myself as a small polar bear... Hmmm.
Oh and use something like a SNIFFER to generate the traffic. Most of
what we
know of as commercial computer's cannot generate more than 70% to 80% capacity on whatever network they are on because of driver overhead and OS latency etc etc etc. It was funny, but I remember testing FDDI on a UnixWARE based platform and watching the driver suck 79% of the system into the floor.
Btw, if you've got a bit of time on your hands, the Click router components have some extremely-low-overhead drivers (for specific ethernet cards under Linux).
Good Point.
They can generate traffic at pretty impressive rates. They used them for testing DOS traffic for a while.
Still there are very few parametric engines that will generate more than 100Mb/S traffic - continuously.
(Most of the driver overhead you see is interrupt latency;
Depends on which OS you are running, and what encapsulation or other packaging/unpackaging is done in the Driver also accounts for a substantial amount of the compute model. If those services are done mostly in HW then the systems I have played with will give you up to about 80% capacity. And on ethernet that is not Collision-Free (i.e.run as full duplex), then you have to deal with the line characteristics so with both engines competing to flood the net you may actually get less than 80% total performance...
click uses an optimized polling style to really cram things through). Also, the new FreeBSD polling patches should make it so you can get more throughput from your drivers when doing tests. I understand there are similar things for Linux.
The Linux Router Project has similar features.
-Dave
-- work: dga@lcs.mit.edu me: dga@pobox.com MIT Laboratory for Computer Science http://www.angio.net/