Question regarding CDC NCM and VNC performance issue

[Hiago De Franco <hiagofranco@gmail.com>]

From: Hiago De Franco <hiago.franco@toradex.com>

Hi,

I hope this email finds you well. I would like to ask a question
regarding the usage of CDC NCM and VCN on an ARM device running the Linux
kernel, connected to a host PC, also running Linux, via USB.

I have successfully set up a CDC NCM connection, where my device acts as
a DHCP server, and the connection is established without any issues.

Now, I have a VNC server running on the device. However, when I connect to
the VNC server, the performance is extremely slow and it also freezes,
making it unusable. Interestingly, when I simultaneously launch iperf3
using the same NCM connection, the VNC performance improves significantly.
The VNC remains smooth as long as iperf3 is active. When iperf3 finishes,
the VNC returns to its frozen or slow state.

I've tested the same setup with Windows 11, and in that case, the VNC
operates normally without any issues. I've also compared the network
traffic of both Windows and Linux connections using Wireshark but haven't
identified anything relevant.

Has anyone encountered a similar issue before? Could this be related to
the size or quantity of transmitted packages? 

Any insights or assistance on this matter would be greatly appreciated.

Thanks,
Hiago