Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (22 chapters)
Mastering Embedded Linux Programming
About the Author
About the Reviewers

Per-process memory usage

There are several metrics to measure the amount of memory a process is using. I will begin with the two that are easiest to obtain— the virtual set size (vss) and the resident memory size (rss), both of which are available in most implementations of the ps and top commands:

  • Vss: called VSZ in the ps command and VIRT in top, is the total amount of memory mapped by a process. It is the sum of all the regions shown in /proc/<PID>/map. This number is of limited interest, since only part of the virtual memory is committed to physical memory at any one time.

  • Rss: called RSS in ps and RES in top, is the sum of memory that is mapped to physical pages of memory. This gets closer to the actual memory budget of the process, but there is a problem, if you add up the Rss of all the processes, you will get an overestimate the memory in use because some pages will be shared.

Using top and ps

The versions of top and ps from BusyBox give very limited information. The examples that...