The Cisco 7200 Series supports process switching, fast switching, and Cisco Express Forwarding (CEF), but does not support any form of distributed switching(hardware switching). The main CPU in the NPE performs all the switching tasks.
The performance of the router is based on the type of NPE you use on the router.
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"Interrupt" CPU is where the CPU normally records fast packet forwarding. As Riyas has noted, normally this CPU usage will correspond with high traffic load (although "high" traffic load depends on the nature of the traffic, your configuration, and how "fast" a NPE you have).
I.e. your high interrupt CPU might just be reflecting the forwarding capacity of your 7200.
Hmm, what you might also want to investigate is why there's 20% of non-interrupt CPU.