svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
ffclock(4)
FFCLOCK(4) BSD Kernel Interfaces Manual FFCLOCK(4)
NAME
FFCLOCK — Feed-forward system clock
SYNOPSIS
options FFCLOCK
DESCRIPTION
The ntpd(8) daemon has been the dominant solution for system clock syn‐
chronisation for many years, which has in turn influenced the design of
the system clock. The ntpd daemon implements a feedback control algo‐
rithm which has been demonstrated to perform poorly in common use cases.
Feed-forward clock synchronisation algorithms implemented by an appropri‐
ate daemon, in concert with the FFCLOCK kernel support, have been shown
to provide highly robust and accurate clock synchronisation. In addition
to time keeping, the FFCLOCK kernel mechanism provides new timestamping
capabilities and the ability to use specialised clocks. Feed-forward
synchronisation is also very well suited for virtualised environments,
reducing the overhead of timekeeping in guests and ensuring continued
smooth operation of the system clock during guest live migration.
The FFCLOCK kernel support provides feed-forward timestamping functions
within the kernel and system calls to support feed-forward synchronisa‐
tion daemons (see ffclock(2)).
Kernel Options
The following kernel configuration options are related to FFCLOCK:
FFCLOCK Enable feed-forward clock support.
Configuration
When feed-forward clock support is compiled into the kernel, multiple
system clocks become available to choose from. System clock configura‐
tion is possible via the kern.sysclock sysctl(8) tree which provides the
following variables:
kern.sysclock.active
Name of the current active system clock which is serving
time. Set to one of the names in kern.sysclock.available in
order to change the default active system clock.
kern.sysclock.available
Lists the names of available system clocks (read-only).
Feed-forward system clock configuration is possible via the
kern.sysclock.ffclock sysctl tree which provides the following variables:
kern.sysclock.ffclock.version
Feed-forward clock kernel version (read-only).
kern.sysclock.ffclock.ffcounter_bypass
Use reliable hardware timecounter as the feed-forward
counter. Will eventually be useful for virtualised environ‐
ment like xen(4), but currently does nothing.
SEE ALSO
clock_gettime(2), ffclock(2), bpf(4), timecounters(4), sysctl(8)
HISTORY
Feed-forward clock support first appeared in FreeBSD 10.0.
AUTHORS
The feed-forward clock support was written by Julien Ridoux
<jridoux@unimelb.edu.au> in collaboration with Darryl Veitch
<dveitch@unimelb.edu.au> at the University of Melbourne under sponsorship
from the FreeBSD Foundation.
This manual page was written by Julien Ridoux <jridoux@unimelb.edu.au>
and Lawrence Stewart <lstewart@FreeBSD.org>.
BSD December 1, 2011 BSD