Sepherosa Ziehau has been doing a lot of work with various processors states to save power on DragonFly. He’s published a summary of how well the various P-state/C-state/mwait settings work. He found that setting a lower C-state can perversely improve performance.
For those saying “but how do I set these lower power states?”:
sysctl machdep.mwait.CX.idle: AUTODEEP
sysctl machdep.cpu_idle_hlt: 1 (or higher)