perfSONAR User Q&A and Other Discussion

[Aaron Wood <>]

Iperf3 (in the stable branches), performs user-level pacing by using a 100ms timer.  Master uses a 1ms timer (and can be set down to 1µs with the --pacing-timer option).  My experience is that the 1ms timer greatly improves smoothness (and can lower drop rates on UDP, especially if you're restricting to a known bottleneck that isn't the local interface).

But user-level pacing works at the "good-put" level, not at the wire-rate.  Whereas when fq-pacing is in use, that's in terms of MAC frames, so as much as 60 bytes larger per frame.

-Aaron

On Sun, May 14, 2017 at 12:18 PM, Brian Tierney <> wrote:

-b works for both TCP and UDP, but --fq-rate works much better for TCP on CentOS7/Debian8 based hosts, as it does kernel-level pacing, not user-level pacing.

On Sat, May 13, 2017 at 7:54 PM, Arman Mohsin <> wrote:

Hi Brian,

Hope all is well. Does the iperf3 -c -b option limit bandwidth for TCP as well or is it ONLY for UDP? I tried to read the documentation in the man page but it is a bit confusing. In the earlier versions of iperf the -b option is used to test only UDP but I am not sure if it supports in the latest version (iperf3)

Regards,

Arman

--

Brian Tierney, http://www.es.net/tierney
Energy Sciences Network (ESnet), Berkeley National Lab
http://fasterdata.es.net

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