Ubuntu Manpage: libpfm - a helper library to develop monitoring tools

NAME

       libpfm - a helper library to develop monitoring tools

SYNOPSIS

       #include <perfmon/pfmlib.h>

DESCRIPTION

This is a helper library used by applications to program specific performance monitoring
events. Those events are typically provided by the hardware or the OS kernel. The most
common hardware events are provided by the Performance Monitoring Unit (PMU) of modern
processors. They can measure elapsed cycles or the number of cache misses. Software
events usually count kernel events such as the number of context switches, or pages
faults.

The library groups events based on which source is providing them. The term PMU is
generalized to any event source, not just hardware sources. The library supports hardware
performance events from most common processors, each group under a specific PMU name, such
as Intel Core, IBM Power 6.

Programming events is usually done through a kernel API, such as Oprofile, perfmon,
perfctr, or perf_events on Linux. The library provides support for perf_events which is
available in the Linux kernel as of v2.6.31. Perf_events supports selected PMU models and
several software events.

At its core, the library provides a simple translation service, whereby a user specifies
an event to measure as a string and the library returns the parameters needed to invoke
the kernel API. It is important to realize that the library does not make the system call
to program the event.

Note: You must first call pfm_initialize() in order to use any of the other provided
functions in the library.

A first part of the library provides an event listing and query interface. This can be
used to discover the events available on a specific hardware platform.

The second part of the library provides a set of functions to obtain event encodings form
event strings. Event encoding depends primarily on the underlying hardware but also on the
kernel API. The library offers a generic API to address the first situation but it also
provides entry points for specific kernel APIs such as perf_events. In that case, it is
able to prepare the data structure which must be passed to the kernel to program a
specific event.

EVENT DETECTION

       When the library is initialized via pfm_initialize(),  it  first  detects  the  underlying
       hardware  and  software  configuration.   Based on this information it enables certain PMU
       support.  Multiple events tables may be activated.

       It is possible to  force  activation  of  a  specific  PMU  (group  of  events)  using  an
       environment variable.

EVENT STRINGS

Events are expressed as strings. Those string are structured and may contain several
components depending on the type of event and the underlying hardware.

String parsing is always case insensitive.

The string structure is defined as follows:

[pmu::][event_name][:unit_mask][:modifier|:modifier=val]

The components are defined as follows:

pmu Optional name of the PMU (group of events) to which the event belongs to. This is
useful to disambiguate events in case events from difference sources have the same
name. If not specified, the first match is used.

event_name
The name of the event. It must be the complete name, partial matches are not
accepted. This component is required.

unit_mask
This designate an optional sub-events. Some events can be refined using sub-events.
Event may have multiple unit masks and it may or may be possible to combine them.
If more than one unit masks needs to be passed, then the [:unit_mask] pattern can
be repeated.

modifier
A modifier is an optional filter which modifies how the event counts. Modifiers
have a type and a value. The value is specified after the equal sign. No space is
allowed. In case of boolean modifiers, it is possible to omit the value true (1).
The presence of the modifier is interpreted as meaning true. Events may support
multiple modifiers, in which case the [:modifier|:modifier=val] pattern can be
repeated. The is no ordering constraint between modifier and unit masks. Modifiers
may be specified before unit masks and vice-versa.

ENVIRONMENT VARIABLES

It is possible to enable certain debug features of the library using environment
variables. The following variables are defined:

LIBPFM_VERBOSE
Enable verbose output. Value must be 0 or 1.

LIBPFM_DEBUG
Enable debug output. Value must be 0 or 1

LIBPFM_DEBUG_STDOUT
Redirect verbose and debug output to the standard output file descriptor (stdout).
By default, the output is directed to the standard error file descriptor (stderr).

LIBPFM_FORCE_PMU
Force a specific PMU model to be activated. In this mode, only that one model is
activated. The value of the variable must be the PMU name as returned by the
pfm_get_pmu_name() function. Note for some PMU models, it may be possible to
specify additional options, such as specific processor models or stepping.
Additional parameters necessarily appears after a comma. For instance,
LIBPFM_FORCE_PMU=amd64,16,2,1.

LIBPFM_ENCODE_INACTIVE
Set this variable to 1 to enable encoding of events for non detected, but
supported, PMUs models.

LIBPFM_DISABLED_PMUS
Provides a list of PMU models to disable. This is a comma separated list of PMU
models. The PMU model is the string in name field of the pfm_pmu_info_t structure.
For instance: LIBPFM_DISABLE_PMUS=core,snb, will disable both the Intel Core and
SandyBridge core PMU support.

AUTHORS

       Stephane Eranian <eranian@gmail.com>
       Robert Richter <robert.richter@amd.com>