get_cyclecount(9)
NAME
- get_cyclecount - get the CPU's fast counter register con
- tents
SYNOPSIS
#include <sys/param.h>
#include <sys/systm.h>
#include <machine/cpu.h>
u_int64_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 in - side 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 se - lected 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-de
- pendent. Some
CPUs (such as the Intel 80486) do not have such a register, - so
get_cyclecount() on these platforms returns the number of - nanoseconds
represented by the structure returned by nanotime(9). - The Pentium processors all use the TSC register.
- The Alpha processors use the PCC register.
- The IA64 processors use the AR.ITC register.
SEE ALSO
HISTORY
The get_cyclecount() function first appeared in FreeBSD 5.0.
AUTHORS
- This manual page was written by Mark Murray <markm@FreeB
- SD.org>.
- BSD November 20, 2000