RE: i.MX8MM Ethernet TX Bandwidth Fluctuations

Hi Frieder,

Sorry, I missed this mail before, I can reproduce this issue at my side, I will try my best to look into this issue.

Best Regards,
Joakim Zhang

-----Original Message-----
From: Frieder Schrempf <redacted>
Sent: 2021年5月6日 22:46
To: dl-linux-imx <redacted>; netdev@vger.kernel.org;
linux-arm-kernel@lists.infradead.org
Subject: i.MX8MM Ethernet TX Bandwidth Fluctuations

Hi,

we observed some weird phenomenon with the Ethernet on our i.MX8M-Mini
boards. It happens quite often that the measured bandwidth in TX direction
drops from its expected/nominal value to something like 50% (for 100M) or ~67%
(for 1G) connections.

So far we reproduced this with two different hardware designs using two
different PHYs (RGMII VSC8531 and RMII KSZ8081), two different kernel
versions (v5.4 and v5.10) and link speeds of 100M and 1G.

To measure the throughput we simply run iperf3 on the target (with a short
p2p connection to the host PC) like this:

	iperf3 -c 192.168.1.10 --bidir

But even something more simple like this can be used to get the info (with 'nc -l
-p 1122 > /dev/null' running on the host):

	dd if=/dev/zero bs=10M count=1 | nc 192.168.1.10 1122

The results fluctuate between each test run and are sometimes 'good' (e.g.
~90 MBit/s for 100M link) and sometimes 'bad' (e.g. ~45 MBit/s for 100M link).
There is nothing else running on the system in parallel. Some more info is also
available in this post: [1].

If there's anyone around who has an idea on what might be the reason for this,
please let me know!
Or maybe someone would be willing to do a quick test on his own hardware.
That would also be highly appreciated!

Thanks and best regards
Frieder

[1]:
https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcommu
nity.nxp.com%2Ft5%2Fi-MX-Processors%2Fi-MX8MM-Ethernet-TX-Bandwidth-
Fluctuations%2Fm-p%2F1242467%23M170563&amp;data=04%7C01%7Cqiang
qing.zhang%40nxp.com%7C5d4866d4565e4cbc36a008d9109da0ff%7C686ea1d
3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637559091463792932%7CUnkno
wn%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1ha
WwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=ygcThQOLIzp0lzhXacRLjSjnjm1FEj
YSxakXwZtxde8%3D&amp;reserved=0