It seems to be pretty closely tied to the network traffic (
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. ;-)