Chapter 1
Parallelism Today
What's in This Chapter?
How parallelism arrived and why parallel programming is feared
Different parallel models that you can use, along with some potential pitfalls this new type of programming introduces
How to predict the behavior of parallel programs
The introduction of multi-core processors brings a new set of challenges for the programmer. After a brief discussion on the power density race, this chapter looks at the top six parallel programming challenges. Finally, the chapter presents a number of different programming models that you can use to add parallelism to your code.
The Arrival of Parallelism
Parallelism is not new; indeed, parallel computer architectures were available in the 1950s. What is new is that parallelism is ubiquitous, available to everyone, and now in every computer.
The Power Density Race
Over the recent decades, computer CPUs have become faster and more powerful; the clock speed of CPUs doubled almost every 18 months. This rise in speed led to a dramatic rise in the power density. Figure 1.1 shows the power density of different generations of processors. Power density is a measure of how much heat is generated by the CPU, and is usually dissipated by a heat sink and cooling system. If the trend of the 1990s were to continue into the twenty-first century, the heat needing to be dissipated would be comparable to that of the surface of the sun — we would be at meltdown! A tongue-in-cheek cartoon competition appeared on an x86 ...
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