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Fackamato

Member

Registered: 2006-03-31

Posts: 579

tcp-vegas congestion control, results

Hi,

(tl;dr: Change TCP congestion algorithm, get good latency over wlan with heavy bandwidth usage)

I've read a bit on www.bufferbloat.net (interesting site), particulary

https://lists.bufferbloat.net/pipermail … 00018.html and
http://www.bufferbloat.net/projects/blo … _TCP_vegas .

So I decided to try for myself, to see if the vegas algorithm is better than the cubic (default) congestion algorithm used in the Linux kernel, in my simple test case. To switch to the vegas algorithm (you can switch them on the fly) just do

$ modprobe -v tcp-vegas
echo vegas > /proc/sys/net/ipv4/tcp_congestion_control

I did this on both the server (GBe > DIR-655) and the laptop (iwlagn/4965 > DIR-655) then started the iperf server on the server and then the iperf client on the laptop. Here are the results:

vegas
[  5]  0.0-60.0 sec   150 MBytes  21.0 Mbits/sec
55 packets transmitted, 55 received, 0% packet loss, time 54065ms
rtt min/avg/max/mdev = 0.361/2.304/4.657/1.015 ms

cubic
[  4]  0.0-60.9 sec   159 MBytes  21.9 Mbits/sec
59 packets transmitted, 59 received, 0% packet loss, time 58042ms
rtt min/avg/max/mdev = 0.451/492.225/638.512/186.448 ms

cubic
[  5]  0.0-60.9 sec   159 MBytes  21.9 Mbits/sec
50 packets transmitted, 50 received, 0% packet loss, time 49053ms
rtt min/avg/max/mdev = 21.644/472.414/803.671/201.180 ms

vegas
[  4]  0.0-60.0 sec   150 MBytes  21.0 Mbits/sec
50 packets transmitted, 50 received, 0% packet loss, time 49072ms
rtt min/avg/max/mdev = 1.134/2.793/5.799/1.149 ms

vegas
[  4]  0.0-60.0 sec   145 MBytes  20.3 Mbits/sec
50 packets transmitted, 50 received, 0% packet loss, time 49066ms
rtt min/avg/max/mdev = 0.635/2.598/6.608/1.287 ms

As you can see, vegas takes a ~1-2mbit/s hit in performance compared to cubic, but the latency is MUCH better in my setup and test case. I suppose tcp-vegas would help me greatly if I download something from the server and game at the same time, or just do anything bandwidth intensive while also wanting low latency apps to work good.

Any thoughts on this?

milomouse

Member

Registered: 2009-03-24

Posts: 940

Website

Re: tcp-vegas congestion control, results

not trying to sidetrack you but being a TCP Vegas variant (and dependant upon it in certain situations) have you tried TCP YeAH? it's what i've been using for a while though i've yet to thoroughly test it's against cubic.

Fackamato

Member

Registered: 2006-03-31

Posts: 579

Re: tcp-vegas congestion control, results

not trying to sidetrack you but being a TCP Vegas variant (and dependant upon it in certain situations) have you tried TCP YeAH? it's what i've been using for a while though i've yet to thoroughly test it's against cubic.

I haven't looked at it, might give it a go as well.