<< Back to man.ChinaUnix.net

Chapter 33. OProfile

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 Red Hat Enterprise Linux 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:

33.1. Overview of Tools

Table 33-1 provides a brief overview of the tools provided with the oprofile package.

CommandDescription
op_help

Displays available events for the system's processor along with a brief description of each.

op_import

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.

opannotateCreates annotated source for an executable if the application was compiled with debugging symbols. Refer to Section 33.5.3 Using opannotate for details.
opcontrol

Configures what data is collected. Refer to Section 33.2 Configuring OProfile for details.

opreport

Retrieves profile data. Refer to Section 33.5.1 Using opreport for details.

oprofiled

Runs as a daemon to periodically write sample data to disk.

Table 33-1. OProfile Commands