Section 17.1. Synchronization

17.1. Synchronization

Solaris runs on a variety of different hardware platforms, including multiprocessor systems based on both the SPARC and Intel processors. Several multiprocessor architectures in existence today offer various trade-offs in performance and engineering complexity in both hardware and software. The current multiprocessor architecture that Solaris supports is the symmetric multiprocessor (SMP) and shared memory architecture, which implements a single kernel shared by all processors and a single memory address space. To support such an architecture, the kernel must synchronize access to critical data to maintain data integrity, coherency, and state. The kernel synchronizes access by defining a lock for a particular kernel data structure or variable and requiring that code reading or writing the data must first acquire the appropriate lock. The holder of the lock is required to release the lock once the data operation has been completed.

The synchronization primitives and associated interfaces are used by virtually all kernel subsystems: device drivers, the dispatcher, process and thread support code, file systems, etc. Insight into what the synchronization objects are and how they are implemented is key to understanding one of the core strengths of the Solaris kernelscalable performance on multiprocessor systems. An equally important component to the scalability equation is the avoidance of locks altogether whenever possible. The use of synchronization locks in the kernel is constantly being scrutinized as part of the development process in kernel engineering, with an eye to minimizing the number of locks required without compromising data integrity.

Several alternative methods of building parallel multiprocessor systems have emerged in the industry over the years. So, in the interest of conveying the issues surrounding the implementation, we need to put things in context. First, we take a brief look at the different parallel systems architectures that are commercially available today, and then we turn to the specifics of support for multiprocessor architectures by the Solaris kernel.