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Chapter 26. OProfile

26.1. Overview of Tools
26.2. Configuring OProfile
26.2.1. Specifying the Kernel
26.2.2. Setting Events to Monitor
26.2.3. Separating Kernel and User-space Profiles
26.3. Starting and Stopping OProfile
26.4. Saving Data
26.5. Analyzing the Data
26.5.1. Using opreport
26.5.2. Using opreport on a Single Executable
26.5.3. Getting more detailed output on the modules
26.5.4. Using opannotate
26.6. Understanding /dev/oprofile/
26.7. Example Usage
26.8. Graphical Interface
26.9. Additional Resources
26.9.1. Installed Docs
26.9.2. Useful Websites
OProfile is a low overhead, system-wide performance monitoring tool. It uses the performance monitoring hardware on the processor to retrieve information about the kernel and executables on the system, such as when memory is referenced, the number of L2 cache requests, and the number of hardware interrupts received. On a Fedora system, the oprofile RPM package must be installed to use this tool.
Many processors include dedicated performance monitoring hardware. This hardware makes it possible to detect when certain events happen (such as the requested data not being in cache). The hardware normally takes the form of one or more counters that are incremented each time an event takes place. When the counter value, essentially rolls over, an interrupt is generated, making it possible to control the amount of detail (and therefore, overhead) produced by performance monitoring.
OProfile uses this hardware (or a timer-based substitute in cases where performance monitoring hardware is not present) to collect samples of performance-related data each time a counter generates an interrupt. These samples are periodically written out to disk; later, the data contained in these samples can then be used to generate reports on system-level and application-level performance.
OProfile is a useful tool, but be aware of some limitations when using it:

26.1. Overview of Tools

Table 26.1, “OProfile Commands” provides a brief overview of the tools provided with the oprofile package.
Command Description
Displays available events for the system's processor along with a brief description of each.
Converts sample database files from a foreign binary format to the native format for the system. Only use this option when analyzing a sample database from a different architecture.
opannotate Creates annotated source for an executable if the application was compiled with debugging symbols. Refer to Section 26.5.4, “Using opannotate for details.
Configures what data is collected. Refer to Section 26.2, “Configuring OProfile” for details.
Retrieves profile data. Refer to Section 26.5.1, “Using opreport for details.
Runs as a daemon to periodically write sample data to disk.
Table 26.1. OProfile Commands