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timer: make timer accuracy configurable

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And make it default to 1min
This commit is contained in:
Lennart Poettering
2013-11-21 22:08:20 +01:00
parent b850b06e1e
commit 9f5eb56a13
7 changed files with 71 additions and 10 deletions
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man/systemd.timer.xml
+58 -4
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@@ -163,7 +163,14 @@
to any of these options, the list of
timers is reset, and all prior
assignments will have no
effect.</para></listitem>
effect.</para>
<para>Note that timers are not
necessarily expired at the precise
time configured with these settings,
as they are subject to the
<varname>AccuracySec=</varname>
setting below.</para></listitem>
</varlistentry>
@@ -171,16 +178,61 @@
<term><varname>OnCalendar=</varname></term>
<listitem><para>Defines realtime
(i.e. wallclock) timers via calendar
(i.e. wallclock) timers with calendar
event expressions. See
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information on the syntax of
calendar event expressions. Otherwise
the semantics are similar to
<varname>OnActiveSec=</varname> and
related settings.</para></listitem>
related settings.</para>
<para>Note that timers are not
necessarily expired at the precise
time configured with this setting,
as it is subject to the
<varname>AccuracySec=</varname>
setting below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>AccuracySec=</varname></term>
<listitem><para>Specify the accuracy
the timer shall elapse with. Defaults
to 1min. The timer is scheduled to
expire within a time window starting
with the time specified in
<varname>OnCalendar=</varname>,
<varname>OnActiveSec=</varname>,
<varname>OnBootSec=</varname>,
<varname>OnStartupSec=</varname>,
<varname>OnUnitActiveSec=</varname> or
<varname>OnUnitInactiveSec=</varname>
and ending the time configured with
<varname>AccuracySec=</varname>
later. Within this time window the
expiry time will be placed at a
host-specific, randomized but stable
position, that is synchronized between
all local timer units. This is done in
order to distribute the wake-up time
in networked installations, as well as
optimizing power consumption to
suppress unnecessary CPU wake-ups. To
get best accuracy set this option to
1us. Note that the timer is still
subject to the timer slack configured
via
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
<varname>TimerSlackNSec=</varname>
setting. See
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. To optimize power
consumption make sure to set this
value as high as possible and as low
as necessary.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Unit=</varname></term>
@@ -208,7 +260,9 @@
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
</para>
</refsect1>