Re: Problems on windows
Nevermind, I find out how to tune iperf to get (more) reliable results:
On XP, 2.02 (Cygwin version) works fine, as long as:
- you set the window size to 96K
- use 4-12 threads
- uset t > 30 to get rid of startup effects.
Your mileage may vary with the window size depending on the latency in
So adding -t 30 -P 4 -w 96K will work for most end users and will test
up to 300 mbit on XP here on SURFnet6. -P 12 will take that further, but
creates more startup effects for ADSL users, so t will need to grow then if you want to cover the complete range of network possibilities for end-users.
I also learnt that the order of the parameters matters(!). -P 4 -w 96K
in the beginning doesn't work, on the end it does.
Maarten Koopmans wrote:
We are using iperf as one of the underlying tools in the SURFnet
Detective (detective.surfnet.nl) and I'm seeing some really strange
behaviour. In our setup we have a bunch of linux servers on 1 GBit,
and when testing from linux clients over the WAN we get between
300-800mbit depending on how many threads, window size etc (using TCP).
Using iperf 2.01 on windows I don't get more than 20 mbit. Using the
-P option crashes that version. Nevermind, I downloaded version 2.02
based on cygwin, and decided to test some more from home. Home is an
ADSL2+ connection 12mbit down, 1mbit up.
Surprisingly, when running iperf 2.02 with multiple threads, my
upstream bandwidth grows as I add more threads. With 1 thread it's
0.70Mbit, but with 4 threads and a window size of 512k I get 2 mbit,
this climbs to 3mbit upstream with 20 threads. With my ADSL2+ this
simply isn't possible (1mbit upstream max), so I suspect "something is
This puts me between a rock and a hard place:
1) multithreaded client (TCP) on WinXp looks unreliable, at least in
the ADSL range
2) single threaded (TCP) on high bandwidth networks is at least an
order of 10 lower on WinXP then the Linux box sitting next to it on
Has anybody else observed this behaviour, or even better, has anybody
a solution for this?
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