This manual applies to OProfile version 0.9.8. OProfile is a profiling system for Linux 2.6 and higher systems on a number of architectures. It is capable of profiling all parts of a running system, from the kernel (including modules and interrupt handlers) to shared libraries to binaries. OProfile can profile the whole system in the background, collecting information at a low overhead. These features make it ideal for profiling entire systems to determine bottle necks in real-world systems.

Many CPUs provide "performance counters", hardware registers that can count "events"; for example, cache misses, or CPU cycles. OProfile provides profiles of code based on the number of these occurring events: repeatedly, every time a certain (configurable) number of events has occurred, the PC value is recorded. This information is aggregated into profiles for each binary image.

Some hardware setups do not allow OProfile to use performance counters: in these cases, no events are available so OProfile operates in timer mode, as described in later chapters. Timer mode is only available in "legacy mode" (see Section 1, “OProfile legacy mode”).