Raspberry Pi 4 drops packets and high ping with SQM

Last month I switched from an old Broadcom Asus router to a Raspberry Pi 4 with the hope It can handle my upgraded internet bandwidth Down/Up: 500/25Mbit.

My setup is like this:

  • RPI4 with case(cooling works fine, thermals always under 40°C)
  • Pi's Lan Port connected to 16 Port switch
  • Wan: TP-Link UE300(Realtek) connected to a Fritzbox 6660 cable modem, also tried an ASIX chipset which performed the same
  • SQM: cake, piece of cake + 350mbit down/15mbit down

The problem is, as soon I fully saturate one of those limits, the Pi will start to drop packets and the ping goes high. The old Asus router did work very well with 150/10 in the same network, so I'm actually out of ideas what could be the problem. What I tried so far, with no success:

  • Testing with dslreports.com, which shows an A+ rating, but the buffer bloat seems to jump between 3ms and 40ms
  • Testing with both ipv4/ipv6, because my ISP only offers DS-lite
  • Testing with ASIX + Realtek Chipset
  • Monitoring Thermals and Load(which seems fine)
  • Doing some tests with uploading/downloading on different clients in the network, saturating the upload limit seems to cause the worst results(a lot of dropped packets)

So I'm actually out of ideas what to try anymore. My last 2 ideas are:

  • Using the Board's Port as wan and the USB Ethernet adapter as lan
  • Maybe the power supply is too weak(It only provides up 5v 2.4A), however I doubt It as the load is never at peak and the frequency seems stable

The way SQM works is it drops packets when you saturate the set speed so that's not unexpected. However the ping shouldn't spike high if your speeds are below what the ISP actually offers.

Can you do a waveform bufferbloat test without SQM enabled and a second one with SQM enabled and the speeds set to 80% of what the first test indicated. Link to the results pages for those tests and see what we are dealing with

Sadly, I was busy during Christmas and forgot about this thread, sorry for that. I did some more tests(same setup with different ISPs), and It seems something is faulty about the cable internet either ISP or the modem, however It's kinda useless to discuss this with my ISP(Vodafone DE) anymore as the hotline is just too incompetent to understand the problem, despite me providing good data(frequent ping latencies plotted over several months). I did a bit more research on my modem, and It really seems the Intel Puma chipsets seem to be kinda crappy as well.

Thankfully, we have a local ISP here that offers FTTH, but they are out of material for now. So hopefully in May I'll have reliable Internet Connection again.

If you have an Intel Puma that is your first problem. Replace the modem with something good and don't look back. Or yeah, get FTTH as soon as you can.