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)
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 · 2026-08-28 17:25:57 UTC
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.
larrik · 2026-08-28 17:23:30 UTC
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.
toast0 · 2026-08-28 17:29:32 UTC
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.
adastra22 · 2026-08-28 18:10:46 UTC
It is so frustrating that this can bring down the rest of the network to the lowest common denominator. I know it is the fault of a cheap switch, not the TV, but still.
toast0 · 2026-08-28 18:41:36 UTC
> It is so frustrating that this can bring down the rest of the network to the lowest common denominator.
It shouldn't? I have 10M to 10G in the same ethernet collision domain everything works at appropriate speeds (my 10G hosts don't always hit 10G cause some of them have anemic cpus, but that's a different story). Most of my switches are cheap gigE switches, not the 10G stuff obviously, so cheap isn't the problem.
Only thing is if some equipment thought ethernet pause frames were a good idea... Send too much traffic to a low speed switch port and get a pause frame will tend to stop all outbound traffic which is not helpful. Not a lot of things send or respect pause frames though...
somehnguy · 2026-08-28 17:38:12 UTC
Yes - I think in cases where you have a good wireless setup at home it's actually preferable to not hardwire the TV. It's easy to get better performance over wifi when the port is only 100mbps.
Aurornis · 2026-08-28 19:01:31 UTC
Gigabit is more expensive, consumes more power, and generates more heat. If a device doesn't need the speed, 100M is a better choice.
Even the most high bitrate streaming services have peak bitrates under 80Mbps, with averages being much lower than that.
alexnewman · 2026-08-28 17:50:12 UTC
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
evulhotdog · 2026-08-28 19:46:16 UTC
Always check the physical layer first!
chasd00 · 2026-08-28 20:10:18 UTC
> Turns out I didn’t plug the sfp+ all the way in.
I don't know why I know this but back in 2011 something not being plugged in all the way was the root reason why neutrinos were detected traveling faster than the speed of light.
"In March 2012 an LNGS seminar was held, confirming the fiber cable was not fully screwed in during data gathering"
Awesome writeup, thanks. I wasn't aware of iperf3 as a tool. This helped me confirm that the 10GbE lines I ran a while ago are in good shape.
I didn't need to change any NIC settings, but I'm on an X540 instead of an E610-XT2
FatherOfCurses · 2026-08-28 18:47:35 UTC
Is there a similar diagnostic that can be run on a Playstation 5? I generally have good download speeds on my network but it seems to take forever to install games on my PS5.
deberon · 2026-08-28 19:17:11 UTC
My guess would be that this has more to do with disk speed if your download speeds are decent. Especially if it’s wired to the internet rather than WiFi. It’s always easy to spot the console user in cross-platform lobbies because of the loading times.
OptionOfT · 2026-08-28 19:18:33 UTC
Playstation's networking capabilities are an absolute mess.
In anticipation for GTA6 I actually bought a PS5 Pro 2 weeks ago. I had to create a separate IPv4-only network because it would not complete the user-sign-up on the device on my IPv4/IPv6 network.
Comments
https://lore.kernel.org/intel-wired-lan/803760bf-04ff-4b23-8...
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
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.
It took me a while because I assumed gigabit had been kind for far longer than it actually was in practice.
It shouldn't? I have 10M to 10G in the same ethernet collision domain everything works at appropriate speeds (my 10G hosts don't always hit 10G cause some of them have anemic cpus, but that's a different story). Most of my switches are cheap gigE switches, not the 10G stuff obviously, so cheap isn't the problem.
Only thing is if some equipment thought ethernet pause frames were a good idea... Send too much traffic to a low speed switch port and get a pause frame will tend to stop all outbound traffic which is not helpful. Not a lot of things send or respect pause frames though...
Even the most high bitrate streaming services have peak bitrates under 80Mbps, with averages being much lower than that.
I don't know why I know this but back in 2011 something not being plugged in all the way was the root reason why neutrinos were detected traveling faster than the speed of light.
"In March 2012 an LNGS seminar was held, confirming the fiber cable was not fully screwed in during data gathering"
https://en.wikipedia.org/wiki/2011_OPERA_faster-than-light_n...
I didn't need to change any NIC settings, but I'm on an X540 instead of an E610-XT2
In anticipation for GTA6 I actually bought a PS5 Pro 2 weeks ago. I had to create a separate IPv4-only network because it would not complete the user-sign-up on the device on my IPv4/IPv6 network.
Absolutely insane.