NAME
get_cyclecount —
get the CPU's fast counter register
contents
SYNOPSIS
#include
<sys/param.h>
#include <sys/systm.h>
#include <machine/cpu.h>
uint64_t
get_cyclecount(void);
DESCRIPTION
Theget_cyclecount()
function uses a register available in most modern CPUs to return a value that
is monotonically increasing inside each CPU.
On SMP systems, there will be a number of separate monotonic sequences, one for each CPU running. The value in the SMP case is selected from one of these sequences, dependent on which CPU was scheduled to service the request.
The speed and the maximum value of each
counter is CPU-dependent. Some CPUs (such as the Intel 80486) do not have
such a register, so
get_cyclecount()
on these platforms returns a (monotonic) combination of numbers represented
by the structure returned by
binuptime(9).
The AMD64 and Intel 64 processors use the
TSC register.
SEE ALSO
HISTORY
The get_cyclecount() function first
appeared in FreeBSD 5.0.
AUTHORS
This manual page was written by Mark Murray <markm@FreeBSD.org>.