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Martin Hope
Flaep
Asked: 2021-09-18 07:05:01 +0800 CST
  • 3

we are trying to setup a 40gbit connection between two servers and get weird cpu behaviour when using iperf. It is also only using around 10Gbit/s of the possible 40.

Server specs:

  • AMD EPYC 7413
  • 8x MultiBitECC 3200 MHz 16384 MB Memory
  • Supermicro H12SSL-CT
  • Intel XL710 40GBe
  • Ubuntu 20.04.3 LTS 5.4.0-84-gene

The Servers are connected directly to each other via fibre. No switches.

Example

host1# iperf -s
host2# iperf -c host1 -i 1 -t 120
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 1.39 GBytes 12.0 Gbits/sec
[ 3] 1.0- 2.0 sec 1.00 GBytes 8.61 Gbits/sec
[ 3] 2.0- 3.0 sec 1.03 GBytes 8.88 Gbits/sec
[ 3] 3.0- 4.0 sec 1.04 GBytes 8.92 Gbits/sec
[ 3] 4.0- 5.0 sec 1021 MBytes 8.56 Gbits/sec
[ 3] 5.0- 6.0 sec 1.05 GBytes 9.01 Gbits/sec
[ 3] 6.0- 7.0 sec 1.02 GBytes 8.78 Gbits/sec
[ 3] 7.0- 8.0 sec 1.02 GBytes 8.74 Gbits/sec
[ 3] 8.0- 9.0 sec 1.01 GBytes 8.69 Gbits/sec
[ 3] 9.0-10.0 sec 1.02 GBytes 8.75 Gbits/sec
[ 3] 10.0-11.0 sec 1.05 GBytes 9.03 Gbits/sec
[ 3] 11.0-12.0 sec 1015 MBytes 8.51 Gbits/sec
[ 3] 12.0-13.0 sec 1.02 GBytes 8.72 Gbits/sec
[ 3] 13.0-14.0 sec 1014 MBytes 8.51 Gbits/sec
[ 3] 14.0-15.0 sec 974 MBytes 8.17 Gbits/sec
[ 3] 0.0-15.0 sec 15.6 GBytes 8.92 Gbits/sec

Around the internet I found the official performance tuning guide from AMD and something from fasterdata.es.net

They suggest to make certain system setting like changing the CPU governor and tcp buffer. I did the changes accordingly and only got 1Gbit/s improvement.

When I checked the CPU clock speed the CPU always clocked down to around 400MHZ when running iperf.

Any suggestion to why either iperf send the CPU sleeping or how I could improve single thread tcp transmission speed? Running multiple tcp threads utilizes the bandwidth better but is not our use case.

thank you

linux tcp iperf
Martin Hope
Flaep
Asked: 2021-04-07 03:08:56 +0800 CST
  • 2

I am trying to set some universal names for the predictable names. I am doing this to be able to have the same interface names on all my machines.

Iam trying to follow "Example 2. /etc/systemd/network/10-dmz.link" from https://www.freedesktop.org/software/systemd/man/systemd.link.html

my files look as follows:

/etc/systemd/network/10-dmz.link

[Match] 
MACAddress=80:ee:73:f1:01:43

[Link]
Name=dmz0

/etc/systemd/network/10-dmz.network

[Match] 
Name=dmz0

[Network]

Address=192.168.25.2/24

After reboot I do not get an interface called dmz0. Systemd-networkd is enabled and setting a IP on another interface with a .network file works.

What am I missing?

thank you

systemd ubuntu-18.04 udevd