MacBook Pro in single-core mode, x86 power management
During this trip, I had a chance to test MacBook Pro with one CPU core disabled. With the first release firmware and OS, MacBook Pro doesn't track its battery very well, but after shutting down one CPU core, MacBook's reported battery power practically hovered in place. It read 1:30 remaining when I shut down the second core and 1:12 about 40 minutes later. That's with wireless off (per FAA regulations, suh) and Energy Saver at the Better Energy Savings setting.
Is this magic or just first-release, math-impaired power management? Decide for yourself, but at your own risk. Install the CHUD tool from the Xcode package. You don't have to install anything else. CHUD adds a System Preferences pane called Processor. Open it and check the "show control in the menu bar" checkbox. Now you can point at the chip in the menu bar and choose Single CPU. The Processor Palette option in that menu pulls up a familiar marching performance chart, but with a twist: Click on the chip icon next to the CPU 2 chart. That's another way to turn the second core on and off.
This trick works for all SMP and multi-core Macs, PowerPC and Intel alike. I did a mild hack to my Xserve's power management to flip the second G5 on and off according to load. Turning cores, CPUs or cache on and off has no effect on the system except to cool it down.
One of the reasons I want to get my hands on an OS X-compatible Darwin x86 kernel is so that I can monitor and manage x86 power states directly. I don't assume there are goodies that Apple isn't using, but now that it's on my turf (x86), I have the skills to check their work and if I can best it for my benefit, I will.
