Debugging my new network, when 10 Gigabit Ethernet Runs at 300 Megabits

tacomagick•5 minutes ago

Might also want to see: https://docs.pixeldrain.com/posts/2024-03-07_network_optimiz...

larrik•32 minutes ago

When I was struggling to figure out why so many of my devices on my gigabit network were only getting 100 megabits, I learned that a lot more of my devices were on 10/100 ethernet than I expected. Including some recent purchases (TV's especially).

It took me a while because I assumed gigabit had been kind for far longer than it actually was in practice.

somehnguy•17 minutes ago

Yes - I think in cases where you have a good wireless setup at home it's actually preferable to not hardware the TV. It's easy to get better performance over wifi when the port is only 100mbps.

toast0•26 minutes ago

TV stuff doesn't tend to need more than 100Mbps, unless you're playing blu-ray 4k discs which have higher peak rates. Saving a buck or two on the SoC adds up for the manufacturer.

alexnewman•5 minutes ago

Recently I found my bilateral Bandwidth was limited from the switch to host. Turns out I didn’t plug the sfp+ all the way in. Amazing it worked at all

ValdikSS•about 2 hours ago

Another example: PCIe ASPM exit latency. Fast LAN speed (because the card does not have time to go into sleep) but low internet speed (manages to enter ASPM if the host is at least 3ms away)

https://lore.kernel.org/intel-wired-lan/803760bf-04ff-4b23-8...

ck2•about 1 hour ago

good old buffer packet size

anyone old enough from dialup modems and RS232 to remember the trick of replacing the 16450 UART with 16550 if you were lucky enough to have it on a socket instead of soldered?

that took it from a 1-byte buffer to 16-bytes, instant speed boost

same idea going from X-modem to Y-modem for transfers, 128bytes vs 1024bytes before checksum

surprised ethernet by now doesn't constantly try to negotiate larger buffer windows

toast0•29 minutes ago

A lot of these drivers were written in a different era and the defaults are less appropriate now.

Having too few receive buffers leaves a trail in diagnostics (if you know to look for it!), having too many gives more subtle problems. But with 10G ethernet, you can get a lot of packets really quickly and the buffer default was probably set for a card doing 100M or 1G and the driver was updated to handle 10G without new defaults. Interrupt modulation is also common now, which is great for throughput, but means packets buffers will get more full.

I feel like segmentation offload is a nice idea, but weirdness always lurks in the shadows and I don't hesitate to turn it off if any weirdness appears. I haven't noticed a perf difference when I turn it off, but I also haven't run great tests.

Debugging my new network, when 10 Gigabit Ethernet Runs at 300 Megabits

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