GET_CYCLECOUNT(9) FreeBSD Kernel Developer's Manual GET_CYCLECOUNT(9)
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
The get_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
binuptime(9)
HISTORY
The get_cyclecount() function first appeared in FreeBSD 5.0.
AUTHORS
This manual page was written by Mark Murray <
[email protected]>.
FreeBSD 14.1-RELEASE-p8 March 15, 2011 FreeBSD 14.1-RELEASE-p8