Book Image

The Art of Writing Efficient Programs

By : Fedor G. Pikus
3 (2)
Book Image

The Art of Writing Efficient Programs

3 (2)
By: Fedor G. Pikus

Overview of this book

The great free lunch of "performance taking care of itself" is over. Until recently, programs got faster by themselves as CPUs were upgraded, but that doesn't happen anymore. The clock frequency of new processors has almost peaked, and while new architectures provide small improvements to existing programs, this only helps slightly. To write efficient software, you now have to know how to program by making good use of the available computing resources, and this book will teach you how to do that. The Art of Efficient Programming covers all the major aspects of writing efficient programs, such as using CPU resources and memory efficiently, avoiding unnecessary computations, measuring performance, and how to put concurrency and multithreading to good use. You'll also learn about compiler optimizations and how to use the programming language (C++) more efficiently. Finally, you'll understand how design decisions impact performance. By the end of this book, you'll not only have enough knowledge of processors and compilers to write efficient programs, but you'll also be able to understand which techniques to use and what to measure while improving performance. At its core, this book is about learning how to learn.
Table of Contents (18 chapters)
1
Section 1 – Performance Fundamentals
7
Section 2 – Advanced Concurrency
11
Section 3 – Designing and Coding High-Performance Programs

The speed of memory: the numbers

Now that we have our benchmarking code to measure the speed of reading and writing into memory, we can collect the results and see how we can get the best performance when accessing data in memory. We begin with random access, where the location of each value we read or write is unpredictable.

The speed of random memory access

The measurements are likely to be fairly noisy unless you run this benchmark many times and average the results (the benchmark library can do that for you). For a reasonable run time (minutes), you will likely see the results that look something like this:

Figure 4.3 – Random read speed as a function of memory size

The benchmark results in Figure 4.3 show the number of words read from memory per second (in billions, on any reasonable PC or workstation you can find today), where the word is a 64-bit integer or a 265-bit integer (long or __m256i, respectively). The same measurements can be alternatively...