> is there an API or syscall to get a list of available cpu frequencies, > that the CPU supports?
No. Not all rate/power adjustments are done in terms of frequencies. Some are done based on bus clock adjustment, or how the memory controller works, or other tricks that are processor specific. Mapping those into a set of sequential numbers would be hard. The relationships of those numbers do not translate into performance values for all workloads evenly. We punted on that crazy problem and instead only supply a knob choosing 0-100 percentage scale in the hw.setperf sysctl; different machines then pick different methods of speed adjustment at different points on the line, and if it is convenient for them they also report the cpu clock rate in hw.cpuspeed (however as I have said, this value is not the final story).
