What does the irqstat graph in munin represent?

Question

What does it mean for this munin graph of weekly irqstat to suddenly go crazy like it does -- is it bad? What are local timer interrupts?

Answer 1

It seems to be pretty closely tied to the network traffic (eth0 and eth1) seen at exactly the same timeframe. Increased network throughput means increased interrupts. Honestly, I wouldn't worry about it unless you're noticing unusually poor system or network performance. Interrupts are a normal part of computer operation.

From §6.2.3 of Understanding the Linux Kernel, 3rd Edition:

…a CPU local timer interrupt signals timekeeping activities related to the local CPU, such as monitoring how long the current process has been running and updating the resource usage statistics.

(That is, keeping track of CPU time for our favourite ps displays. ;-)