A Primer on Memory Consistency and Cache Coherence, Daniel Sorin, Mark Hill, David Wood

In a shared memory system, each of the processor cores may read and write to a single shared address space. For a shared memory machine, the memory consistency model defines the architecturally visible behavior of its memory system. Consistency definitions provide rules about loads and stores (or memory reads and writes) and how they act upon memory. As part of supporting a memory consistency model, many machines also provide cache coherence protocols that ensure that multiple cached copies of data are kept up-to-date. The goal of this primer is to provide readers with a basic understanding of consistency and coherence. This understanding includes both the issues that must be solved as well as a variety of solutions. We present both high-level concepts as well as specific, concrete examples from real-world systems.

This second edition reflects a decade of advancements since the first edition and includes, among other more modest changes, two new chapters: one on consistency and coherence for non-CPU accelerators (with a focus on GPUs) and one that points to formal work and tools on consistency and coherence.

In a shared memory system, each of the processor cores may read and write to a single shared address space. For a shared memory machine, the memory consistency model defines the architecturally visible behavior of its memory system. Consistency definitions provide rules about loads and stores (or memory reads and writes) and how they act upon memory. As part of supporting a memory consistency model, many machines also provide cache coherence protocols that ensure that multiple cached copies of data are kept up-to-date. The goal of this primer is to provide readers with a basic understanding of consistency and coherence. This understanding includes both the issues that must be solved as well as a variety of solutions. We present both high-level concepts as well as specific, concrete examples from real-world systems.

This second edition reflects a decade of advancements since the first edition and includes, among other more modest changes, two new chapters: one on consistency and coherence for non-CPU accelerators (with a focus on GPUs) and one that points to formal work and tools on consistency and coherence.

The emphasis is on algorithmic issues, so the authors start by defining a taxonomy that places previous policies into two broad categories, which they refer to as coarse-grained and fine-grained policies. Each of these categories is then divided into three subcategories that describe different approaches to solving the cache replacement problem, along with summaries of significant work in each category. Richer factors, including solutions that optimize for metrics beyond cache miss rates, that are tailored to multi-core settings, that consider interactions with prefetchers, and that consider new memory technologies, are then explored. The book concludes by discussing trends and challenges for future work. This book, which assumes that readers will have a basic understanding of computer architecture and caches, will be useful to academics and practitioners across the field.

The emphasis is on algorithmic issues, so the authors start by defining a taxonomy that places previous policies into two broad categories, which they refer to as coarse-grained and fine-grained policies. Each of these categories is then divided into three subcategories that describe different approaches to solving the cache replacement problem, along with summaries of significant work in each category. Richer factors, including solutions that optimize for metrics beyond cache miss rates, that are tailored to multi-core settings, that consider interactions with prefetchers, and that consider new memory technologies, are then explored. The book concludes by discussing trends and challenges for future work. This book, which assumes that readers will have a basic understanding of computer architecture and caches, will be useful to academics and practitioners across the field.