See http://en.wikipedia.org/wiki/Pegging; I don't think we're talking the cribbage definition...

Anyway, the ondemand regulator runs the clock up to some maximum with actual load; naturally, it lags a little, like an automatic transmission: step on the gas, start accelerating, lose acceleration while shifting, then really accelerate. The maximum is either 400/133 (with no DSP tasks) or 330/220 (with any DSP tasks).

Performance simply keeps it at the same maximum; 400 without DSP, but dropping to 330 whenever there's a DSP task.

If you know your DSP tasks are cool at 133 MHz rather than 220, you can actually disable frequency regulation to maintain 400 MHz all the time. AFAIK, this is fine for normal usage, where the DSP only handles mp3 decoding and BT HSP; it might not do so well with DSP-based A2DP, but I really don't know.... works just fine for DSP-based A2DP as well!