Advanced Synchronization in Mac OS X: Extending UNIX to SMP and Real-Time

Throughout the years, as Unix has grown and evolved so has computer hardware. The 4.4BSD-Lite2 distribution had no support for two features that are becoming more and more important: SMP and real-time processing.

With the release Mac OS X Apple has made extensive alterations to our kernel in order to support both SMP and real-time processing. These alterations affected both the BSD and Mach portions of our kernel, as well as shaping our driver system, IOKit.

These changes range from scheduling policies, enabling support for kernel preemption, altering locking hierarchies, and defining new serialization primitives, as well as designing a driver architecture that allows developers to easily make their drivers SMP and preemption safe.