Profiling
Eventually all embedded systems projects reach the optimization phase where a good profiler can come in handy. OProfile is a systemwide profiler for Linux that's capable of profiling user space applications, kernel code, and loadable modules. The OProfile software package consists of kernel code, userspace daemon, and utilities. Fortunately, no kernel patching is required as OProfile is part of the stock Linux 2.6 kernel.

A typical OProfile session looks like:

opcontrol --vmlinux     =/path/to/vmlinux
opcontrol --start
#execute your code
opreport -l /path/to/mybinary
opcontrol --reset

The first two commands start the profiler, opreport prints the results, and the last command resets the data. OProfile is a powerful profiler with many features, all of which are outside the scope of this article, but I encourage you to read more at oprofile.sourceforge.net/doc/in dex.html.

An important tip for embedded developers is that they can filter profiling results by modules, which can be a driver, an application, or the kernel itself. Note that OProfile is a statistical profiler, which means it samples program-counter values on interrupt (usually timer interrupt), so you must run the code for some minimal time period to get meaningful results.

If your hardware is like most, and has performance counters that can generate an interrupt on such events as cache miss, you can find not only the most CPU-intensive pieces of code, but also the most cache inefficient. Unless you use an exotic CPU, OProfile will already have support for performance counters of that CPU.

Binding it all together
Although it's not necessary and can even make things more complex, if you're more comfortable with a monolithic IDE-like software package that can do all your daily tasks using keyboard shortcuts and menus, the simplest way to do this is to create a new Emacs menu called "Embedded" and add all your scripts to that menu. The example in Listing 3 (Emacs Lisp code that should be added to your .emacs file) illustrates this.

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