The reason for this performance differences is that iperf3 is single
threaded, so all parallel streams will use a single core. At 40G you will
be core limited
To test 40G with iperf3, I do the following:
Start 3 servers:
iperf3 -s -p 5101
iperf3 -s -p 5102
iperf3 -s -p 5103
and then run 3 clients, using the "-T" flag to label the output:
iperf3 -c hostname -T s1 -p 5101 &; iperf3 -c hostname -T s2 -p 5102 &;
iperf3 -c hostname -T s3 -p 5103 &;
We have also updated the Fasterdata website:
https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/iperf-and-iperf3/iperf3-at-speeds-about-10gbps
The Github issue has also been updated.
Cheers,
Jon
On Thu, Jun 2, 2016 at 3:19 PM, Jeffrey Lane <jeffrey.l...@canonical.com>
wrote:
> I am running into a problem where there is a remarkable difference in
> reported throughput when using iperf2 vs iperf3.
>
> With iperf2, and about 16 - 20 threads, I can get, reliably, between
> 32 and 35 Gb/s on a 40Gb segment. with iperf3 on exactly the same
> hardware, I only get 4Gb/s, sometimes I can get up to 11Gb/s.
>
> Is there some trick to getting more accurate results out of iperf3?
>
> There is nothing special about the network, in fact, the network
> consists of two servers with 40Gb cards connected directly, no
> intervening switch. There is no routing issue that I can find, the
> 40Gb ports are on a completely different address space than the
> onboard 1Gb ports, AND the 1Gb ports on each server can't talk to each
> other. Physically the ONLY way these servers can talk to each other
> is across the 40Gb link.
>
> Another person opened a bug for this:
> https://github.com/esnet/iperf/issues/408
>
> and there are now three people on that thread reporting the same issues.
>
> Any suggestions for how to debug or resolve this?
>
>
> --
> "Entropy isn't what it used to be."
>
> Jeff Lane -
> Server Certification Lead, Warrior Poet, Biker, Lover of Pie
> Phone: 919-442-8649
> Ubuntu Ham: W4KDH Freenode IRC: bladernr or
> bladernr_
> gpg: 1024D/3A14B2DD 8C88 B076 0DD7 B404 1417 C466 4ABD 3635 3A14 B2DD
>
>
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