Hi Stef, Thanks for the reply! However, I think the gap is way too large to be explained by overhead, etc. Here are the results from some other tests. I started with: tc qdisc add dev eth2 root tbf rate 1.9mbit buffer 20Kb/8 limit 15Kb Here are the average transfer rates measured over approx 20 seconds (again according to PerfMon) as I change the "1.9mbit" to other values while performing a large download: Mbit Kb/s ----- ------ 2.5 360 2.0 360 1.9 360 1.8 240 1.5 240 1.4 240 1.3 180 1.2 180 The lines really are that flat. There is nothing resembling the graphs on your site. Mine has the low-res, stair-step effect that you can see by graphing the above numbers. I can't seem to find any "mbit" number that will actually produce a cap at exactly 2mbit. I will try a both different type NIC and Debian at some point today. Thanks for your help! Dan Farino Sr. System Engineer Stamps.com, Inc. Santa Monica, CA -----Original Message----- From: Stef Coene [mailto:stef.coene@docum.org] Sent: Tuesday, November 12, 2002 8:09 AM To: Dan Farino; lartc@mailman.ds9a.nl Subject: Re: Extremely inaccurate results using either TBF or HTB > > I am getting extremely inaccurate results from my setup: > > - RedHat 8.0 on a Compaq ProLiant 1600, dual PII/450, Intel Dual 100 NIC > - I've tried both SMP and non-SMP kernels. > - I'm using the updated tc from the HTB home page. > - I'm using the HTB that comes with the RH8 kernel. > > Here's what's happening. If I, for instance: > > tc qdisc add dev eth2 root tbf rate 1.9mbit buffer 20Kb/8 limit > 15Kb > > Then my download rate goes at 360,000 bytes/s, which, by my > calculations, is 2.77mbit. I am using Win2k perfmon to test the speed. > The line is flat and the speed is very consistent (consistently *wrong*, > unfortunately...) > > Immediately after, I do: > > tc qdisc change dev eth2 root tbf rate 1.8mbit buffer 20Kb/8 limit > 15Kb > > My download speed is then 243,000 bytes/s, or 1.85mbit. Again, very > flat, consistent line. > > > I have played with the parameters on both TBF and HTB in many different > configurations. I always seem to have a large jump between 1.8-1.9. I > can't find any number between those two that will actually produce a > 2mbit limit. I know 1.85 is close to 2.0, but is this the expected > margin of error? (Then again, 2.77 isn't close to 1.9 at all, so I hope > not!) > > Has anyone else experienced anything like this? I did some tests with htb and tbf : http://www.docum.org/stef.coene/qos/tests/tbf/ http://www.docum.org/stef.coene/qos/tests/htb/index.html And the accuracy was very good. I did the tests on a debian system with a custom kernel and tc command. How did you measure the throughput? I use the iptables counters so I know exactly what passes the box. If you download a file from the internet with a ftp client, there can be overhead due to retransmission, control packets, .... So the speed you measure with the ftp client may be lower then the real connection speed. Stef -- stef.coene@docum.org "Using Linux as bandwidth manager" http://www.docum.org/ #lartc @ irc.oftc.net _______________________________________________ LARTC mailing list / LARTC@mailman.ds9a.nl http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
