i.MX8MM Ethernet TX Bandwidth Fluctuations

[Joakim Zhang]

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 <frieder.schrempf at kontron.de>
> Sent: 2021年5月6日 22:46
> To: dl-linux-imx <linux-imx at nxp.com>; netdev at vger.kernel.org;
> linux-arm-kernel at 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&data=04%7C01%7Cqiang
> qing.zhang%40nxp.com%7C5d4866d4565e4cbc36a008d9109da0ff%7C686ea1d
> 3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637559091463792932%7CUnkno
> wn%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1ha
> WwiLCJXVCI6Mn0%3D%7C1000&sdata=ygcThQOLIzp0lzhXacRLjSjnjm1FEj
> YSxakXwZtxde8%3D&reserved=0