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 reserved:28;
};
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.
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.
