[Solved] High CPU (soft-irq)

I just changed my network topology and added a PC behind a openwrt router, downloads from the PC's perspective have slowed down from around 35 MB/s to 25. When it's downloading I see high load on the router, and it mostly seems to be in kernel land.

Is there anything I can tune to reduce load?

Depends on what your network looks like, and what software's running on the device.

What router is that?
Do you use SQM?

The router is a asus rt-n56u. I think this build of openwrt predates sqm, I don’t even have an init script for it.

Under the display options on htop setup, selected the "detailed cpu time" so you can see more granular information about the cpu usage, whether it's some kernel land routine or whether it's interrupt processing

It looks like the cpu is mostly used by soft-irq.

Network tx/rx processing likely. Possible causes

  • SQM or any other QOS
  • Lots of iptables rules
  • You're using a not-very-powerful router with an old 500mhz 32 bit mips74kc cpu dating from 2011

You can try to enable software flow offloading on the main firewall tab.

If that doesn't help, without meaning to be facetious, get a newer and more powerful router

3 Likes

"Routing/NAT Offloading" did the trick, thanks!

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