I've found a way to get SMP working. It is experimental, use at your own risk!
Once the system is installed, add the following drivers to /System/Library/Extension with a kext installation tool:
- NullCPUPowerManagement.kext from https://tgwbd.org/darwin/extensions.html (you will need to compile it) : it solve the panic during boot when there are more than 1 cpu.
- VoodooTSCSync.kext from http://forum.voodooprojects.org/index.p ... 794.0.html : it solve the TSC synchronization problem you get randomly which prevents the OS GUI to work. Don't forget to adjust the number of CPU you will set as explain in the link (shortly = num cpu - 1).
using Geekbench, I have a true performance improvement : about 3 time better on multi-threaded tests vs mono-threaded ones on a 4 core.