pmc_get_info() returns the number of counters in the system or information on a specified counter
ctr. The possible values for
op are:
PMC_INFO_NCOUNTERS
When querying the number of counters in the system, ctr is ignored and argp is of type int *. Upon return, the integer pointed to by argp will contain the number of counters that are available in the system.
PMC_INFO_CPUCTR_TYPE
When querying the type of a counter in the system,
ctr refers to the counter being queried, and
argp is of type
int *. Upon return, the integer pointed to by
argp will contain the implementation-dependent type of the specified counter.
If
ctr is -1, the integer pointed to by
argp will contain the machine-dependent type describing the CPU or counter configuration.
PMC_INFO_COUNTER_VALUE
When querying the value of a counter in the system, ctr refers to the counter being queried, and argp is of type uint64_t *. Upon return, the 64-bit integer pointed to by argp will contain the value of the specified counter.
PMC_INFO_ACCUMULATED_COUNTER_VALUE
When querying the value of a counter in the system, ctr refers to the counter being queried, and argp is of type uint64_t *. Upon return, the 64-bit integer pointed to by argp will contain the sum of the accumulated values of specified counter in all exited subprocesses of the current process.
pmc_control() manipulates the specified counter
ctr in one of several fashions. The
op parameter determines the action taken by the kernel and also the interpretation of the
argp parameter. The possible values for
op are:
PMC_OP_START
Starts the specified ctr running. It must be preceded by a call with PMC_OP_CONFIGURE. argp is ignored in this case and may be NULL.
PMC_OP_STOP
Stops the specified ctr from running. argp is ignored in this case and may be NULL.
PMC_OP_CONFIGURE
Configures the specified
ctr prior to running.
argp is a pointer to a
struct pmc_counter_cfg.
struct pmc_counter_cfg {
pmc_evid_t event_id;
pmc_ctr_t reset_value;
uint32_t flags;
};
event_id
is the event ID to be counted.
reset_value
is a value to which the counter should be reset on overflow (if supported by the implementation). This is most useful when profiling (see PMC_OP_PROFSTART, below). This value is defined to be the number of counter ticks before the next overflow. So, to get a profiling tick on every hundredth data cache miss, set the event_id to the proper value for “dcache-miss” and set reset_value to 100.
PMC_OP_PROFSTART
Configures the specified ctr for use in profiling. argp is a pointer to a struct pmc_counter_cfg as in PMC_OP_CONFIGURE, above. This request allocates a kernel counter, which will fail if any process is using the requested counter. Not all implementations or counters may support this option.
PMC_OP_PROFSTOP
Stops the specified ctr from being used for profiling. argp is ignored in this case and may be NULL.