NAME

SYNOPSIS

#include <perfmon/pfmlib.h>

DESCRIPTION

The libpfm library is a helper library which can be used by applications to program the IA-64 Performance Monitoring Unit (PMU). While it is being developed on Linux in conjunction with the Linux/ia64 subsystem. It is generic enough to be used on other IA-64 operating systems. It is important to realize that the library does not make the actual kernel calls to program the PMU, it simply helps you figure out which PMU registers to use to measure certain events. On Linux/ia64, for instance, it does not make any perfmonctl call.

There are two categories of PMU registers. The performance monitoring data registers (PMD) are used to collects counts or serve as hardware buffers. The performance monitoring control registers (PMCS) are used to indicate what events need to be monitored. Programming the PMU consists in setting up the PMC registers to monitor certain events. The PMDS are commonly set to zero unless sampling is used.

The number of PMC and PMD registers varies from one implementation of the IA-64 architecture to another. The association of PMC to PMD can also change. Moreover the number and encoding of events can also widely change. Finally, the structure of a PMC register can also change. All these factors make it quite difficult to write monitoring tools.

This library is designed to simplify the programming of the PMC registers by hiding the complexity behind simple interfaces. The library does this without limiting accessibility to model specific features by using a layered design.

The library is structured in two layers. The common layer provides an interface that is shared across all PMU models. This layer is good enough to setup simple monitoring sessions which count occurrences of events. Then, there is a model-specific layer which gives access to the model-specific features. For instance, on Itanium, you can use the library to setup the registers for the Branch Trace Buffer. Model-specific interfaces have the abbreviated PMU model name in their names. For instance, pfm_ita2_get_event_umask() is an Itanium2 (ita2) specific function.

When the library is initialized, it automatically probes the host CPU and enables the right set of interfaces.

The common interface is defined in the pfmlib.h header file. Model-specific interfaces are defined in model-specific header files. For instance, pfmlib_itanium2.h provides the Itanium2 interface.

AUTHOR