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Chapter 20. OProfile

20.1. Overview of Tools
20.2. Configuring OProfile
20.2.1. Specifying the Kernel
20.2.2. Setting Events to Monitor
20.2.3. Separating Kernel and User-space Profiles
20.3. Starting and Stopping OProfile
20.4. Saving Data
20.5. Analyzing the Data
20.5.1. Using opreport
20.5.2. Using opreport on a Single Executable
20.5.3. Getting more detailed output on the modules
20.5.4. Using opannotate
20.6. Understanding /dev/oprofile/
20.7. Example Usage
20.8. OProfile Support for Java
20.8.1. Profiling Java Code
20.9. Graphical Interface
20.10. OProfile and SystemTap
20.11. Additional Resources
20.11.1. Installed Docs
20.11.2. 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 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:

20.1. Overview of Tools

Table 20.1, “OProfile Commands” provides a brief overview of the tools provided with the oprofile package.
Table 20.1. OProfile Commands
Command Description
ophelp
Displays available events for the system's processor along with a brief description of each.
opimport
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 20.5.4, “Using opannotate for details.
opcontrol
Configures what data is collected. Refer to Section 20.2, “Configuring OProfile” for details.
opreport
Retrieves profile data. Refer to Section 20.5.1, “Using opreport for details.
oprofiled
Runs as a daemon to periodically write sample data to disk.