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Slow ethernet under windows, normal under Debian
My ethernet speeds are lower than expected on this computer. There are two ethernet adapters on this motherboard, one 2.5Gbps and a gigabit adapter. They have different manufacturers and run completely different drivers.
Internet speed tests and LAN throughput tests (with iperf under WSL) hover around ~550Mbps. A Macbook Pro, with the same ethernet cable on the same port on the gateway, hit 780Mbps down over the internet.
So to eliminate a hardware issue, I installed Debian 10.9 on a spare disk today - the throughput over LAN magically jumped to 980-990Mbit/s. This is on the same computer, with the same cable, on the same port on either side - just reboot into a different OS and the speed doubles.
I'm at a loss here - I've disabled LSO for ipv4/6, energy efficient ethernet, and a host of other things. This is under W10 ver 2009, 19042.985.