RE: i.MX8MM Ethernet TX Bandwidth Fluctuations

Hi Frieder,

For NXP release kernel, I tested on i.MX8MQ/MM/MP, I can reproduce on L5.10, and can't reproduce on L5.4.
According to your description, you can reproduce this issue both L5.4 and L5.10? So I need confirm with you.

Best Regards,
Joakim Zhang

-----Original Message-----
From: Joakim Zhang <redacted>
Sent: 2021年5月12日 19:59
To: Frieder Schrempf <redacted>; dl-linux-imx
[off-list ref]; netdev@vger.kernel.org;
linux-arm-kernel@lists.infradead.org
Subject: 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

quoted

-----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).

quoted

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%2Fcomm
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nity.nxp.com%2Ft5%2Fi-MX-Processors%2Fi-MX8MM-Ethernet-TX-Bandwidth-

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