10.7.4 Power Management and Sandy Bridge CPUs

It's been a week since the 10.7.4 update, and an issue has cropped up with Core i5 and i7 Sandy Bridge CPUs. As part of this release, Apple updated the power management drivers. These new drivers are effecting performance, as some CPUs are stuck at a 16x multiplier, thus limiting them to a maximum clock speed of 1.6 GHz. When we discovered the issue, we released a temporary workaround on the tonymacx86.com forum while working on a permanent solution. We are now happy to announce our permanent solution.

SpeedStep is a trademark for a series of dynamic frequency scaling technologies built into some Intel microprocessors that allow the clock speed of the processor oto be dynamically changed (to different P-states) by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat dissipation. Enhanced Intel SpeedStep is sometimes abbreviated as EIST.
Source: Wikipedia

The Secondary System Description Table or SSDT is a continuation of the Differentiated System Description Table, or DSDT, allowing the the motherboard manufacturer or OEM to provide the base support in one table (DSDT) and add smaller system options in other tables (SSDT). As such they use the SSDT to provide speed stepping and power configuration.

The Chimera bootloader will either read the SSDT from the motherboard's BIOS/UEFI, use the SSDTs generated by boot keys provided by the MultiBeast UserDSDT boot.plist, or a user provided SSDT. As part of the 10.7.4 update, some Sandy Bridge Socket 1155 i5/i7 CPUs have issues with the BIOS/UEFI SSDT and need a properly edited one to override its configuration. NOTE: Core i3 and i5-2400 CPUs are known to work properly with the BIOS/UEFI SSDT, and don't need this fix.

In order to make optimization easy for the average user, we've prepared 3 SSDT files, included in MultiBeast 4.5.0. The first is for Core i5 systems running at stock speeds. The next is for Core i7 systems also running at stock speeds. The final one is for over clocked Core i5 or Core i7 systems. The specific SSDT.aml file installs into the /Extra folder and will initiate SpeedStep properly in 10.7.4. One of these optimized SSDTs are recommended for users of the following CPUs: i5-2500, i5-2500K, i5-2550K, i7-2600, i7-2600K, i7-2700K.
After installing one of these SSDTs you can verify that SpeedStep is working on Sandy Bridge CPUs by installing Project OS X's new FakeSMC, FakeSMC Plugins, and HWMonitor app, available in the latest MultiBeast. After installation of these files, launch HWMonitor and click the live cpu Frequencies and Multiplier to view in the menubar as shown below. Keep in mind that Turbo frequencies will not appear.

Special thanks to Greggen and everyone in the community for sharing their knowledge- testing and editing SSDTs in the past week. We're interested in any feedback using these new tools. Please add your comments and results in this thread and in the brand new SSDT subforum.

For discussions on this and other topics, register today at tonymacx86.com!