diff options
Diffstat (limited to 'static/freebsd/man4/ffclock.4 3.html')
| -rw-r--r-- | static/freebsd/man4/ffclock.4 3.html | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/static/freebsd/man4/ffclock.4 3.html b/static/freebsd/man4/ffclock.4 3.html new file mode 100644 index 00000000..c3f3477d --- /dev/null +++ b/static/freebsd/man4/ffclock.4 3.html @@ -0,0 +1,113 @@ +<table class="head"> + <tr> + <td class="head-ltitle">FFCLOCK(4)</td> + <td class="head-vol">Device Drivers Manual</td> + <td class="head-rtitle">FFCLOCK(4)</td> + </tr> +</table> +<div class="manual-text"> +<section class="Sh"> +<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1> +<p class="Pp"><code class="Nm">FFCLOCK</code> — + <span class="Nd">Feed-forward system clock</span></p> +</section> +<section class="Sh"> +<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1> +<p class="Pp"><code class="Cd">options FFCLOCK</code></p> +</section> +<section class="Sh"> +<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1> +<p class="Pp">The <a class="Xr">ntpd(8)</a> 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.</p> +<p class="Pp">Feed-forward clock synchronisation algorithms implemented by an + appropriate daemon, in concert with the <code class="Nm">FFCLOCK</code> + kernel support, have been shown to provide highly robust and accurate clock + synchronisation. In addition to time keeping, the + <code class="Nm">FFCLOCK</code> 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.</p> +<p class="Pp">The <code class="Nm">FFCLOCK</code> kernel support provides + feed-forward timestamping functions within the kernel and system calls to + support feed-forward synchronisation daemons (see + <a class="Xr">ffclock(2)</a>).</p> +<section class="Ss"> +<h2 class="Ss" id="Kernel_Options"><a class="permalink" href="#Kernel_Options">Kernel + Options</a></h2> +<p class="Pp">The following kernel configuration options are related to + <code class="Nm">FFCLOCK</code>:</p> +<p class="Pp"></p> +<dl class="Bl-tag Bl-compact"> + <dt id="FFCLOCK"><a class="permalink" href="#FFCLOCK"><code class="Dv">FFCLOCK</code></a></dt> + <dd>Enable feed-forward clock support.</dd> +</dl> +</section> +<section class="Ss"> +<h2 class="Ss" id="Configuration"><a class="permalink" href="#Configuration">Configuration</a></h2> +<p class="Pp">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 <var class="Va">kern.sysclock</var> + <a class="Xr">sysctl(8)</a> tree which provides the following variables:</p> +<div class="Bd-indent"> +<dl class="Bl-tag"> + <dt id="kern.sysclock.active"><var class="Va">kern.sysclock.active</var></dt> + <dd>Name of the current active system clock which is serving time. Set to one + of the names in <var class="Va">kern.sysclock.available</var> in order to + change the default active system clock.</dd> + <dt id="kern.sysclock.available"><var class="Va">kern.sysclock.available</var></dt> + <dd>Lists the names of available system clocks (read-only).</dd> +</dl> +</div> +<p class="Pp">Feed-forward system clock configuration is possible via the + <var class="Va">kern.sysclock.ffclock</var> sysctl tree which provides the + following variables:</p> +<div class="Bd-indent"> +<dl class="Bl-tag"> + <dt id="kern.sysclock.ffclock.version"><var class="Va">kern.sysclock.ffclock.version</var></dt> + <dd>Feed-forward clock kernel version (read-only).</dd> + <dt id="kern.sysclock.ffclock.ffcounter_bypass"><var class="Va">kern.sysclock.ffclock.ffcounter_bypass</var></dt> + <dd>Use reliable hardware timecounter as the feed-forward counter. Will + eventually be useful for virtualised environment like + <a class="Xr">xen(4)</a>, but currently does nothing.</dd> +</dl> +</div> +</section> +</section> +<section class="Sh"> +<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE + ALSO</a></h1> +<p class="Pp"><a class="Xr">clock_gettime(2)</a>, <a class="Xr">ffclock(2)</a>, + <a class="Xr">bpf(4)</a>, <a class="Xr">timecounters(4)</a>, + <a class="Xr">sysctl(8)</a></p> +</section> +<section class="Sh"> +<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1> +<p class="Pp">Feed-forward clock support first appeared in + <span class="Ux">FreeBSD 10.0</span>.</p> +</section> +<section class="Sh"> +<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1> +<p class="Pp">The feed-forward clock support was written by + <span class="An">Julien Ridoux</span> + <<a class="Mt" href="mailto:jridoux@unimelb.edu.au">jridoux@unimelb.edu.au</a>> + in collaboration with <span class="An">Darryl Veitch</span> + <<a class="Mt" href="mailto:dveitch@unimelb.edu.au">dveitch@unimelb.edu.au</a>> + at the University of Melbourne under sponsorship from the FreeBSD + Foundation.</p> +<p class="Pp">This manual page was written by <span class="An">Julien + Ridoux</span> + <<a class="Mt" href="mailto:jridoux@unimelb.edu.au">jridoux@unimelb.edu.au</a>> + and <span class="An">Lawrence Stewart</span> + <<a class="Mt" href="mailto:lstewart@FreeBSD.org">lstewart@FreeBSD.org</a>>.</p> +</section> +</div> +<table class="foot"> + <tr> + <td class="foot-date">December 1, 2011</td> + <td class="foot-os">FreeBSD 15.0</td> + </tr> +</table> |