get_cyclecount (9)

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Copyright (c) 2000 Mark R V Murray
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(The comments found at the beginning of the groff file "man9/get_cyclecount.9freebsd".)

NAME

get_cyclecount - get the CPU's fast counter register contents

SYNOPSIS

In sys/param.h In sys/systm.h In machine/cpu.h Ft uint64_t Fn get_cyclecount void

DESCRIPTION

The Fn 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 Fn 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 Fn get_cyclecount function first appeared in Fx 5.0 .

AUTHORS

This manual page was written by An Mark Murray Aq markm@FreeBSD.org .