NAME

     get_cyclecount — get the CPU's fast counter register contents

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 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>.