OProfile

OProfile is a system-wide profiler for Linux. It collects performance data by monitoring CPU performance counters and other events. OProfile is designed to be low-overhead, meaning it has minimal impact on the performance of the system being profiled. It can be used to profile applications, libraries, and the operating system kernel itself. The data collected by OProfile can help identify performance bottlenecks and optimize code.

The core of OProfile consists of a kernel module and a user-space daemon. The kernel module intercepts performance counter interrupts and samples the program counter and other relevant information. This information is then passed to the user-space daemon, which collects and aggregates the data. A separate user-space utility, `opreport`, is used to process the collected data and generate reports. These reports can show which functions or lines of code are consuming the most CPU time.

OProfile supports various event types, including hardware performance counters (like CPU cycles, cache misses, and branch mispredictions) and software-based events. Its ability to profile the entire system, including kernel code, makes it a powerful tool for understanding complex performance issues that might span user and kernel space. It is often used by developers and system administrators to tune software for better performance.