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diff --git a/share/man/man4/ffclock.4 b/share/man/man4/ffclock.4 new file mode 100644 index 0000000..9110c16 --- /dev/null +++ b/share/man/man4/ffclock.4 @@ -0,0 +1,129 @@ +.\" Copyright (c) 2011 The University of Melbourne +.\" All rights reserved. +.\" +.\" This documentation was written by Julien Ridoux at the University of +.\" Melbourne under sponsorship from the FreeBSD Foundation. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd December 1, 2011 +.Dt FFCLOCK 4 +.Os +.Sh NAME +.Nm FFCLOCK +.Nd Feed-forward system clock +.Sh SYNOPSIS +.Cd options FFCLOCK +.Sh DESCRIPTION +The +.Xr ntpd 8 +daemon has been the dominant solution for system clock synchronisation for many +years, which has in turn influenced the design of the system clock. +The ntpd daemon implements a feedback control algorithm which has been +demonstrated to perform poorly in common use cases. +.Pp +Feed-forward clock synchronisation algorithms implemented by an appropriate +daemon, in concert with the +.Nm +kernel support, have been shown to provide highly robust and accurate clock +synchronisation. +In addition to time keeping, the +.Nm +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. +.Pp +The +.Nm +kernel support provides feed-forward timestamping functions within the kernel +and system calls to support feed-forward synchronisation daemons +.Po see +.Xr ffclock 2 +.Pc . +.Ss Kernel Options +The following kernel configuration options are related to +.Nm : +.Pp +.Bl -tag -width ".Dv FFCLOCK" -compact +.It Dv FFCLOCK +Enable feed-forward clock support. +.El +.Ss Configuration +When feed-forward clock support is compiled into the kernel, multiple system +clocks become available to choose from. +System clock configuration is possible via the +.Va kern.sysclock +.Xr sysctl 8 +tree which provides the following variables: +.Bl -tag -width " " -offset indent +.It Va kern.sysclock.active +Name of the current active system clock which is serving time. +Set to one of the names in +.Va kern.sysclock.available +in order to change the default active system clock. +.It Va kern.sysclock.available +Lists the names of available system clocks +.Po +read only +.Pc . +.El +.Pp +Feed-forward system clock configuration is possible via the +.Va kern.sysclock.ffclock +sysctl tree which provides the following variables: +.Bl -tag -width " " -offset indent +.It Va kern.sysclock.ffclock.version +Feed-forward clock kernel version +.Po +read only +.Pc . +.It Va kern.sysclock.ffclock.ffcounter_bypass +Use reliable hardware timecounter as the feed-forward counter. +Will eventually be useful for virtualised environment like +.Xr xen 4 , +but currently does nothing. +.El +.Sh SEE ALSO +.Xr clock_gettime 2 , +.Xr ffclock 2 , +.Xr bpf 4 , +.Xr timecounters 4 , +.Xr sysctl 8 +.Sh HISTORY +Feed-forward clock support first appeared in +.Fx 10.0 . +.Sh AUTHORS +.An -nosplit +The feed-forward clock support was written by +.An Julien Ridoux Aq jridoux@unimelb.edu.au +in collaboration with +.An Darryl Veitch Aq dveitch@unimelb.edu.au +at the University of Melbourne under sponsorship from the FreeBSD Foundation. +.Pp +This manual page was written by +.An Julien Ridoux Aq jridoux@unimelb.edu.au +and +.An Lawrence Stewart Aq lstewart@FreeBSD.org . |