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sys_macosx: add option to run chronyd as real-time process

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Adds option -P to chronyd on MacOS X which can be used to enable the
thread time constraint scheduling policy. This near real-time scheduling
policy removes a 1usec bias from the 'System time' offset.
This commit is contained in:
Bryan Christianson
2015-08-25 08:32:14 +12:00
committed by Miroslav Lichvar
parent 5039f959e0
commit b9cfdaf666
5 changed files with 78 additions and 13 deletions
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26
chrony.texi.in
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@@ -1039,9 +1039,11 @@ not correct the clock.
This option displays @code{chronyd's} version number to the terminal and
exits.
@item -P <priority>
This option will select the SCHED_FIFO real-time scheduler at the
specified priority (which must be between 0 and 100). This mode is
supported only on Linux.
On Linux, this option will select the SCHED_FIFO real-time scheduler at the
specified priority (which must be between 0 and 100). On Mac OS X, this option
must have either a value of 0 (the default) to disable the thread time
constraint policy or 1 for the policy to be enabled. Other systems do not
support this option.
@item -m
This option will lock chronyd into RAM so that it will never be paged
out. This mode is only supported on Linux.
@@ -2910,13 +2912,15 @@ is used.
@node sched_priority directive
@subsection sched_priority
The @code{sched_priority} directive will select the SCHED_FIFO real-time
scheduler at the specified priority (which must be between 0 and 100).
This mode is supported only on Linux.
On Linux, the @code{sched_priority} directive will select the SCHED_FIFO
real-time scheduler at the specified priority (which must be between 0 and
100). On Mac OS X, this option must have either a value of 0 (the default) to
disable the thread time constraint policy or 1 for the policy to be enabled.
Other systems do not support this option.
This directive uses the Linux sched_setscheduler() system call to
instruct the kernel to use the SCHED_FIFO first-in, first-out
real-time scheduling policy for @code{chronyd} with the specified priority.
On Linux, this directive uses the sched_setscheduler() system call to instruct
the kernel to use the SCHED_FIFO first-in, first-out real-time scheduling
policy for @code{chronyd} with the specified priority.
This means that whenever @code{chronyd} is ready to run it will run,
interrupting whatever else is running unless it is a higher priority
real-time process. This should not impact performance as @code{chronyd's}
@@ -2924,6 +2928,10 @@ resource requirements are modest, but it should result in lower and
more consistent latency since @code{chronyd} will not need to wait for the
scheduler to get around to running it. You should not use this unless
you really need it. The sched_setscheduler man page has more details.
On Mac OS X, this directive uses the thread_policy_set() kernel call to specify
real-time scheduling. As noted for Linux, you should not use this directive
unless you really need it.
@c }}}
@c {{{ server
@node server directive