Solaris™ Internals: Core Kernel Components

9.2. The Kernel Dispatcher

The dispatcher is the kernel code segment that manages queues of runnable kernel threads, called dispatch queues; places the highest-priority runnable thread on a processor for execution; and manages the recalculation of thread priorities that are based on execution time, sleep time, and time spent on the queue waiting for a processor. The context switching of threads on and off processors is driven by the dispatcher code.

Early versions of Solaris 2 implemented a simple, global dispatch queue that was shared by all processors on a multiprocessor system. Scalability and dispatch latency, especially for real-time threads, was less than optimal because of the coarse-grained locking. A single scheduling lock for the dispatch ...