netdev - Re: Rx issues with Linux Bridge and thunderbolt-net

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Date: Thu, 7 Dec 2023 14:37:58 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Arjun Mehta <arjunmeht@...il.com>
Cc: netdev@...r.kernel.org
Subject: Re: Rx issues with Linux Bridge and thunderbolt-net

On Thu, 7 Dec 2023 12:57:08 -0700
Arjun Mehta <arjunmeht@...il.com> wrote:

> Hi there, I’d like to report what I believe to be a bug with either Linux Bridge (maybe and/or thunderbolt-net as well).
> 
> Problem: Rx on bridged Thunderbolt interface are blocked
> 
> Reported Behavior:
> Tested on Proxmox host via iperf3, between B550 Vision D-P and MacBook Pro (2019 intel). On a direct interface, thunderbolt bridge Tx and Rx speeds are equal and full speed (in my case 9GB/s each). However, when a thunderbolt bridge is passed through via Linux Bridge to a VM or container (in my case a Proxmox LXC container or VM) the bridge achieves full Tx speeds, but Rx speeds are reporting limited to ~30kb/s
> 
> Expected:
> The VM/CT should have the same general performance for Tx AND Rx as the host
> 
> Reproducing:
> - Setup for the bridge was done by following this guide: https://gist.github.com/scyto/67fdc9a517faefa68f730f82d7fa3570
> - Both devices on Thunderbolt interfaces have static IPs
> - VM is given the same IP, but unique MAC address
> - BIOS has Thunderbolt security mode set to “No security”
> 
> Further reading:
> The problem is outlined more with screenshots and further details in this Reddit post: https://www.reddit.com/r/Proxmox/comments/17kq5st/slow_rx_speed_from_thunderbolt_3_port_to_vm_over/.
> 
> Please let me know if there is any further action I can do to help investigate or where else I can direct the bug/concern

Most likely this is a hardware issue on the thunderbolt interface where it will not
allow sending with a different source MAC address.  Some Wifi interfaces have this
problem.

Is Promox using a kernel from upstream Linux repository directly.
Netdev developers are unwilling to assist if there are any non-upstream kernel modules in use.