This is not causing me any problem, it's more a matter of interest. When I switched from the 2.6.18.8 (latest 2.6 stable kernel) to the 2.6.30.5 kernel (both 32 bit), I noticed something strange about the cpu usage being reported on the linode "Cpu usage - last 24 hours" graph.

With 2.6.18.8, the graph of baseline cpu usage is very spiky going between barely over zero usage up to about 0.5% usage. (yes, you burst users have got to love me!).
With the 2.6.30.5 kernel, the graph is almost a flat line at 0.5% usage. There is a very minor blip down about once every two minutes, for just one data sample.

Is this a real effect, or just the way measurements are taken? Has the later kernel taken a big decision to trade predictability for raw cpu cycles? Is the earlier kernel just specially tuned to reduce usage? What's going on here?

The graph is below - ignore the slightly larger spikes, that's when I was actually doing something. The kernel switch is at around 17:00.

I see a similar thing, except for me the "base line" is about 1.5% CPU. As far as I can recall, it showed up something like 6 months ago when I did an upgrade (I think it was at the time the weak SSH key issue was going on). I'm running Debian 4, kernel 2.6.18.8.