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Feed-forward clock synchronisation algorithms implemented by an appropriate 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 synchronisation daemons (see ffclock(2) ).
FFCLOCK | |
Enable feed-forward clock support. | |
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 environment like xen(4), but currently does nothing. | |
This manual page was written by Julien Ridoux <Mt jridoux@unimelb.edu.au> and Lawrence Stewart <Mt lstewart@FreeBSD.org>.
FFCLOCK (4) | December 1, 2011 |
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