i.MX8MM Ethernet TX Bandwidth Fluctuations

[Joakim Zhang]

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 <qiangqing.zhang at nxp.com>
> Sent: 2021年5月12日 19:59
> To: Frieder Schrempf <frieder.schrempf at kontron.de>; dl-linux-imx
> <linux-imx at nxp.com>; netdev at vger.kernel.org;
> linux-arm-kernel at 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
> 
> > -----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%2Fcomm
> > u
> >
> 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