LIBPFM(3)

NAME
pfm_get_event_attr_info - get event attribute information

SYNOPSIS
#include <perfmon/pfmlib.h>

int pfm_get_event_attr_info(int idx, int attr, pfm_os_t os, pfm_event_attr_info_t *info);

DESCRIPTION
This function returns in info information about the attribute designated by attr for the event specified in idx and the os layer in os.

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.

The pfm_event_attr_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_attr_t              type;
        int                     idx;
        pfm_attr_ctrl_t         ctrl;
        int                     reserved1;
        struct {
                int             is_dfl:1;
                int             is_precise:1;
                int             is_speculative:2;
		int		support_hw_smpl:1;
		int		support_no_mods:1;
                int             reserved:26;
        };
        union {
                uint64_t        dfl_val64;
                const char      *dfl_str;
                int             dfl_bool;
                int             dfl_int;
        };
} pfm_event_attr_info_t;

The fields of this structure are defined as follows:

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

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

equiv
    Certain attributes may be just variations of other attributes for the same event. They may be provided as handy shortcuts to avoid supplying a long list of attributes. For those attributes, this field is not NULL and contains the complete equivalent attribute string. This string, once appended to the event name, may be used library calls requiring an event string.

code
    This is the raw attribute code. For PFM_ATTR_UMASK, this is the unit mask code. For all other attributes, this is an opaque index.

type
    This is the type of the attribute. Attributes represent either sub-events or extra filters that can be applied to the event. Filters (also called modifiers) may be tied to the event or the PMU register the event is programmed into. The type of an attribute determines how it must be specified. The following types are defined:

    PFM_ATTR_UMASK
        This is a unit mask, i.e., a sub-event. It is specified using its name. Depending on the event, it may be possible to specify multiple unit masks.

    PFM_ATTR_MOD_BOOL
        This is a boolean attribute. It has a value of 0, 1, y or n. The value is specified after the equal sign, e.g., foo=1. As a convenience, the equal sign and value may be omitted, in which case this is equivalent to =1.

    PFM_ATTR_MOD_INTEGER
        This is an integer attribute. It has a value which must be passed after the equal sign. The range of valid values depends on the attribute and is usually specified in its description.

idx This is the attribute index. It is identical to the value of attr passed to the call and is provided for completeness.

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_attr_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_ATTR_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_dfl
    This field indicates whether or not this attribute is set by default. This applies mostly for PFM_ATTR_UMASK. If a unit mask is marked as default, and no unit mask is specified in the event string, then the library uses it by default. Note that there may be multiple defaults per event depending on how unit masks are grouped.

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

is_speculative
    This bitfield indicates whether or not the attribute includes occurrences happening during speculative execution for both wrong and correct paths. Given that this kind of event information is not always available from vendors, this field uses multiple bits. A value of PFM_EVENT_INFO_SPEC_NA indicates that speculation information is not available. A value of PFM_EVENT_INFO_SPEC_TRUE indicates that the attribute counts during speculative execution. A value of PFM_EVENT_INFO_SPEC_FALSE indicates that the attribute does not count during speculative execution.

support_hw_smpl
    This boolean field indicates that the attribute (in this case a umask) supports hardware sampling. That means the hardware can sample this event+umasks without involving the kernel at each sample.

support_no_mods
    This boolean field indicates that the attribute (in this case a umask) does not support any hardware or software modifiers, such as privilege level filters, sampling, precise sampling, and such. This is necessary when select umasks of an event have more restrictions than others, e.g., the event and most umasks support modifiers except a few umasks.

dfl_val64, dfl_str, dfl_bool, dfl_int
    This union contains the value of an attribute. For PFM_ATTR_UMASK, the is the unit mask code, for all other types this is the actual value of the attribute.

ctrl
    This field indicates which layer or source controls the attribute. The following sources are defined:

    PFM_ATTR_CTRL_UNKNOWN
        The source controlling the attribute is not known.

    PFM_ATTR_CTRL_PMU
        The attribute is controlled by the PMU hardware.

    PFM_ATTR_CTRL_PERF_EVENT
        The attribute is controlled by the perf_events kernel interface.

reserved
    These fields must be set to zero.

RETURN

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

ERRORS

PFMLIB_ERR_NOINIT
    Library has not been initialized properly.

PFMLIB_ERR_INVAL
    The idx or attr arguments are invalid or info is NULL or size is not zero.

PFM_ERR_NOTSUPP
    The requested os layer has not been detected on the host system.

AUTHOR
Stephane Eranian <eranian@gmail.com>