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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 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

     nanotime(9)

HISTORY

     The get_cyclecount() function first appeared in FreeBSD 5.0.

AUTHORS

     This manual page was written by Mark Murray 〈markm@FreeBSD.org〉.