100% CPU usage ONLY when Sonos is connected

[DennyK]

I have a very weird problem on my RT-AC68u running merlin 380.69. This happened in 380.68_4 as well, I thought upgrading might fix it but no luck.

The weird part is this problem only occurs when I have my Sonos Play:1 connected via 2.4Ghz wifi!

With the Sonos connected, I get ksoftirqd consuming 100% CPU on cpu0 when I run a speedtest, but ONLY when downloading. This limits my download speed to 350Mbps while my uploads are ~930Mbps as they should be. Yes, I confirmed that NAT acceleration is on, switch control says "CTF (Cut Through Forwarding) and FA (Flow Acceleration) accelerator are enabled." QoS is completely off, VPN servers are off, WPS is off, not using WDS or radius. Also no USB devices plugged in.

If I unplug the Sonos and then turn the 2.4Ghz radio off and back on, the problem goes away and I get my full download speeds. I tried messing with literally every 2.4Ghz professional setting in the GUI and nothing fixes it, only removing the Sonos does the trick.

Any ideas?

 

[DennyK]

I just tested and confirmed this doesn't happen when plugged in to ethernet. Doesn't help me much as that room isn't wired, but good to know.

Also disabling STP doesn't fix it.

 

[john9527]

IIRC Sonos uses a variation of the old 'g' protocol with some extensions. I would have more expected the Sonos to get locked out during the speedtest, but possibly they are doing something to try and ensure continued communications.

 

[joegreat]

IIRC Sonos uses a variation of the old 'g' protocol with some extensions. I would have more expected the Sonos to get locked out during the speedtest, but possibly they are doing something to try and ensure continued communications.

I had some issues in the past but since I have put the SonosNet (own Mesh Network not using my WLAN) onto a channel 1 (which is not used by me) things are working great for years - across several router types and many, many firmware updates.

I recall that Sonos reacted erratic in some cases when I did firmware updates and Sonos devices where on - unplugging them from power and doing the firmware update without active Sonos devices did the trick.
Then I reconnect the Sonos devices one by one (with a few minutes in-between of each).

Long story short: using SonosNet Mesh Network on a free channel and not your own Wireless Network might be an option...

 

[DennyK]

I only have one Sonos device and it's connected via wifi, so there shouldn't be any SonosNet mesh at all-- it's using its sole wifi radio to connect to my LAN. Like I said if I connect it via ethernet the problem goes away.

I originally thought it might be some sort of packetstorm from the Sonos STP stuff, which is a pretty common issue, but enabling/disabling STP on the router makes no difference and that's only supposed to be a problem with multiple Sonoses plugged in to ethernet anyway, not a single device on wifi.

It really is a bizarre problem, because my LAN works perfectly fine with the Sonos on wifi. The only impact is that downloads from the internet max out sirq and are thus limited to ~350Mbps. And only downloads, uploads to the internet are fine!

I feel like it's got to be a bug in the firmware somewhere, something about the Sonos on LAN wifi disables the NAT offloading/CTF/FA on downloads from the WAN.

 

[DennyK]

Nobody else has a wifi-connected Sonos device here? Or maybe nobody else has gigabit internet to expose the problem?

 

[joegreat]

Nobody else has a wifi-connected Sonos device here? Or maybe nobody else has gigabit internet to expose the problem?

I run Gbit network in my flat (all Cat 6a cabling) but I to not use my WIFI but Sonos-Net (their Mesh) to connect all 6 Sonos devices wireless.

 

[DennyK]

If you connect one of your Sonoses (Sonosi?) by wifi, does that limit your WAN download speeds to <400Mbps?