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clocks (7)
>> clocks (7) ( FreeBSD man: Макропакеты и соглашения )
BSD mandoc
NAME
clocks
- various system timers
SYNOPSIS
#include <time.h>
DESCRIPTION
HZ
is not part of the application interface in
BSD .
There are many different real and virtual (timekeeping) clocks with
different frequencies:
The scheduling clock.
This is a real clock with frequency that happens to be 100.
It is not available to applications.
The statistics clock.
This is a real clock with frequency that happens to be 128.
It is not directly available to applications.
The clock reported by
clock(3).
This is a virtual clock with a frequency that happens to be 128.
Its actual frequency is given by the macro
CLOCKS_PER_SEC
Note that
CLOCKS_PER_SEC
may be floating point.
Do not use
clock(3)
in new programs under
Fx .
It is feeble compared with
getrusage(2).
It is provided for
ANSI
conformance.
It is implemented by calling
getrusage(2)
and throwing away information and resolution.
The clock reported by
times(3).
This is a virtual clock with a frequency that happens to be 128.
Its actual frequency is given by the macro
CLK_TCK
(deprecated; do not use) and by
sysconf (SC_CLK_TCK);
and by
sysctl(3).
Note that its frequency may be different from
CLOCKS_PER_SEC
Do not use
times(3)
in new programs under
Fx .
It is feeble compared with
gettimeofday(2)
together with
getrusage(2).
It is provided for
POSIX
conformance.
It is implemented by calling
gettimeofday(2)
and
getrusage(2)
and throwing away information and resolution.
The profiling clock.
This is a real clock with frequency 1024.
It is used mainly by
moncontrol(3),
kgmon(8)
and
gprof(1).
Applications should determine its actual frequency using
sysctl(3)
or by reading it from the header in the profiling data file.
The mc146818a clock.
This is a real clock with a nominal frequency of 32768.
It is divided down to give the statistic clock and the profiling clock.
It is not available to applications.
The microseconds clock.
This is a virtual clock with frequency 1000000.
It is used for most timekeeping in
BSD and is exported to applications in
getrusage(2),
gettimeofday(2),
select(2),
getitimer(2),
etc.
This is the clock that should normally be used by
BSD applications.
The i8254 clock.
This is a real clock/timer with a nominal frequency of 1193182.
It has three independent time counters to be used.
It is divided down to give the scheduling clock.
It is not available to applications.
The TSC clock (64-bit register) on fifth-generation or later x86 systems.
This is a real clock with a frequency that is equivalent to the number of
cycles per second of the CPU(s).
Its frequency can be found using the
machdep.tsc_freq
sysctl, if it is available.
It is used to interpolate between values of the scheduling clock.
It can be accessed using the
PMIOTSTAMP
request of
perfmon(4).
The ACPI clock.
This is a real clock/timer with a nominal frequency of 3579545.
It is accessed via a 24 or 32 bit register.
Unlike the TSC clock, it maintains a constant tick rate even when the CPU
sleeps or its clock rate changes.
It is not available to applications.
Summary: if
HZ
is not 1000000 then the application is probably using the wrong clock.
