This chapter is dedicated to the correct and reliable communication of values in shared-memory multiprocessors. Relevant correctness properties of the memory system of shared-memory multiprocessors include coherence, the memory consistency model (henceforth also referred to as the memory model), and the reliable execution of synchronization primitives. Since chip multiprocessors are designed as shared-memory multi-core systems, this chapter targets correctness issues not only in symmetric multiprocessors (SMPs) or large-scale cache coherent distributed shared-memory systems (cc-NUMAs and COMAs) covered in Chapter 5, but also in chip multiprocessors with core multi-threading (CMPs) covered in Chapter 8.
The correctness of a shared-memory multi-threaded program must be independent of the relative execution speed of its threads, because of the numerous unpredictable events that can disrupt the execution of any one thread, such as DVFS (dynamic voltage and frequency scaling), thermal emergencies, conflicts for hardware and software resources, interrupts, exceptions, kernel activity, thread scheduling, data allocation delays, and interactions with other running programs. If a multi-threaded program is written for a dedicated machine in which timing is highly predictable and the program is written in a way that takes timing into account for its correctness (such as, possibly, in real-time systems), many conclusions of this chapter should be revised. In other words, the target software throughout this chapter is portable shared-memory multi-threaded programs written for general-purpose or multi-purpose machines and includes the operating system kernel.
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