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.
The IA64 processors use the
AR.ITC
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
⟨markm@FreeBSD.org⟩.