Sampling

The interfaces described in this section enable the return of data from the counters to the application. Counter data resides in an opaque data structure named cpc_buf_t. This data structure takes a snapshot of the state of counters in use by a bound set and includes the following information:

• The 64–bit values of each counter

• The timestamp of the most recent hardware snapshot

• A cumulative CPU cycle counter that counts the number of CPU cycles the processor has used on the bound set

cpc_buf_t *cpc_buf_create(cpc_t *cpc, cpc_set_t *set);
int cpc_buf_destroy(cpc_t *cpc, cpc_buf_t *buf);
int cpc_set_sample(cpc_t *cpc, cpc_set_t *set, cpc_buf_t *buf);

The cpc_buf_create() function creates a buffer that stores data from the set specified in cpc_set_t. The cpc_buf_destroy() function frees the memory that is associated with the given cpc_buf_t. The cpc_buf_sample() function takes a snapshot of the counters that are counting on behalf of the specified set. The specified set must already be bound and have a buffer created before calling the cpc_buf_sample() function.

Sampling into a buffer does not update the preset of the requests that are associated with that set. When a buffer is sampled with the cpc_buf_sample() function, then unbound and bound again, counts start from the request's preset as in the original call to the cpc_set_add_request() function.