1941 high cpu from interrupts even with no traffic

Chris Campbell · ‎12-11-2022

I have a 1941 that has high CPU load from interrupts with no traffic. I started out with a clean configuration and it is running IOS 15.8(3)M7. It has about 89% CPU usage even without traffic, but it's almost all interrupt. It has a very simple configuration on it right now with just overloaded NAT.

c1941#sh proc cpu sorted

CPU utilization for five seconds: 89%/88%; one minute: 89%; five minutes: 89%
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
117 1227998664 1059828547 1158 6.15% 5.99% 6.00% 0 i2c console redi
32 36244 6212 5834 0.31% 0.42% 0.28% 132 SSH Process
115 43403940 2940634 14760 0.23% 0.27% 0.27% 0 ILPM
34 6065420 57452742 105 0.23% 0.23% 0.25% 0 ARP Input

What could be causing this?

MaxShantar · ‎12-11-2022

If you are experiencing high CPU usage on your Cisco 1941 due to interrupts and you do not see any traffic that could be causing this, there are a few steps you can take to troubleshoot the issue:

First, check the interface counters to see if there is any unusual activity or errors on the interfaces. This can help identify if there is a specific interface that is causing the issue.

Next, try disabling any unnecessary services or features on the device to see if that reduces the CPU usage.

You can also try resetting the device to its factory default settings and reconfiguring it to see if that resolves the issue.

If the problem persists, you may need to upgrade the device's firmware to the latest version to ensure that you have the latest bug fixes and performance improvements.

Joseph W. Doherty · ‎12-11-2022

No traffic at all? I.e. all interfaces show zero traffic in last five minutes?

BTW, "interrupt" is "fast path" processing, Cisco does work to move some highly utilized processes in it, but usually all of those revolve around traffic forwarding.

I recall (?), for example, "seeing" routers, years ago, showing high CPU for IP processing when doing packet fragmentation, but later this CPU jumped to "interrupt" where the "cause" wasn't as easy to identify.