NAME

       pfm_get_event_info - get event information

SYNOPSIS

       #include <perfmon/pfmlib.h>

       int pfm_get_event_info(int idx, pfm_os_t os, pfm_event_info_t *info);

DESCRIPTION

       This  function returns in info information about a specific event designated by its opaque
       unique identifier in idx for the operating system specified in os.

       The pfm_event_info_t structure is defined as follows:
       typedef struct {
               const char              *name;
               const char              *desc;
               const char              *equiv;
               size_t           size;
               uint64_t                code;
               pfm_pmu_t               pmu;
               pfm_dtype_t             dtype
               int                     idx;
               int                     nattrs;
               struct {
                 unsigned int is_precise:1;
                 unsigned int reserved_bits:31;
               };
       } pfm_event_info_t;

       The fields of this structure are defined as follows:

       name   This is the name of the event. This is a read-only string.

       desc   This is the description of the event. This is a read-only string.  It  may  contain
              multiple sentences.

       equiv  Certain  events  may  be  just variations of actual events. They may be provided as
              handy shortcuts to avoid supplying a long list of  attributes.  For  those  events,
              this field is not NULL and contains the complete equivalent event string.

       code   This  is  the  raw  event  code. It should not be confused with the encoding of the
              event. This field represents only the event selection code, it does not include any
              unit mask or attribute settings.

       pmu    This  is  the  identification of the PMU model this event belongs to. It is of type
              pfm_pmu_t. Using this value and the pfm_get_pmu_info function, it  is  possible  to
              get PMU information.

       dtype  This  field  returns  the  representation  of  the  event  data.  By default, it is
              PFM_DATA_UINT64.

              idx This is the event unique opaque identifier. It is identical to the  idx  passed
              to the call and is provided for completeness.

       nattrs This  is  the  number of attributes supported by this event. Attributes may be unit
              masks or modifiers. If the event has not attribute, then the value of this field is
              simply 0.

       size   This  field  contains  the size of the struct passed. This field is used to provide
              for extensibility of the struct without compromising backward  compatibility.   The
              value  should  be  set  to  sizeof(pfm_event_info_t).  If  instead, a value of 0 is
              specified, the library assumes the struct passed is  identical  to  the  first  ABI
              version  which  size  is  PFM_EVENT_INFO_ABI0. Thus, if fields were added after the
              first ABI, they will not be set by the library. The library does check  that  bytes
              beyond what is implemented are zeroes.

       is_precise
              This bitfield indicates whether or not the event support precise sampling.  Precise
              sampling is a hardware mechanism that avoids instruction address  skid  when  using
              interrupt-based sampling. When the event has umasks, this field means that at least
              one umask supports precise  sampling.  On  Intel  X86  processors,  this  indicates
              whether the event supports Precise Event-Based Sampling (PEBS).

       The pfm_os_t enumeration provides the following choices:

       PFM_OS_NONE
              The  returned  information  pertains  only  to  what  the PMU hardware exports.  No
              operating system attributes is taken into account.

       PFM_OS_PERF_EVENT
              The returned information includes  the  actual  PMU  hardware  and  the  additional
              attributes exported by the perf_events kernel interface.  The perf_event attributes
              pertain only the PMU hardware.  In case perf_events is not detected,  an  error  is
              returned.

       PFM_OS_PERF_EVENT_EXT
              The   returned   information   includes   all   of  what  is  already  provided  by
              PFM_OS_PERF_EVENT plus all the software attributes controlled by perf_events,  such
              as sampling period, precise sampling.

RETURN

       If  successful,  the function returns PFM_SUCCESS and event information in info, otherwise
       it returns an error code.

ERRORS

       PFMLIB_ERR_NOINIT
              Library has not been initialized properly.

       PFMLIB_ERR_INVAL
              The idx argument is invalid or info is NULL or size is not zero.

       PFMLIB_ERR_NOTSUPP
              The requested os is not detected or supported.

AUTHOR

       Stephane Eranian <eranian@gmail.com>

                                          December, 2009                                LIBPFM(3)