NAME

cpucycles - count CPU cycles

SYNOPSIS

#include <cpucycles.h>

long long count = cpucycles();
long long persecond = cpucycles_persecond();
const char *implementation = cpucycles_implementation();

Link with -lcpucycles. Old systems may also need -lrt.

DESCRIPTION

cpucycles() returns an estimate for the number of CPU cycles that have occurred since an unspecified time in the past (perhaps system boot, perhaps program startup).

Accessing true cycle counters can be difficult on some CPUs and operating systems. cpucycles() does its best to produce accurate results, but selects a low-precision counter if the only other option is failure.

cpucycles_persecond() returns an estimate for the number of CPU cycles per second. This estimate comes from /etc/cpucyclespersecond if that file exists, otherwise from various OS mechanisms, otherwise from the cpucyclespersecond environment variable if that is set, otherwise 1000000000.

cpucycles_implementation() returns the name of the counter in use: e.g., "amd64-pmc".

cpucycles is actually a function pointer. The first call to cpucycles() or cpucycles_persecond() or cpucycles_implementation() selects one of the available counters and updates the cpucycles pointer accordingly. Subsequent calls to cpucycles() are thread-safe.

SEE ALSO

gettimeofday(2), clock_gettime(2)