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.
---
chrony.texi.in | 7 ++++---
chronyd.8.in | 7 ++++---
sys.c | 2 ++
sys_macosx.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
sys_macosx.h | 2 +-
5 files changed, 65 insertions(+), 7 deletions(-)
diff --git a/chrony.texi.in b/chrony.texi.in
index 0b31bb6..89fe5e1 100644
--- a/chrony.texi.in
+++ b/chrony.texi.in
@@ -1039,9 +1039,10 @@ 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 MacOSX, 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.
diff --git a/chronyd.8.in b/chronyd.8.in
index 387ea21..b18d87c 100644
--- a/chronyd.8.in
+++ b/chronyd.8.in
@@ -40,9 +40,10 @@ A summary of the options supported by \fBchronyd\fR is
included below.
.TP
\fB\-P\fR \fIpriority\fR
-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 MacOSX, 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.
.TP
.B \-m
This option will lock chronyd into RAM so that it will never be paged out.
diff --git a/sys.c b/sys.c
index 9de9ee1..5e04c35 100644
--- a/sys.c
+++ b/sys.c
@@ -124,6 +124,8 @@ void SYS_SetScheduler(int SchedPriority)
{
#if defined(LINUX) && defined(HAVE_SCHED_SETSCHEDULER)
SYS_Linux_SetScheduler(SchedPriority);
+#elif defined(MACOSX)
+ SYS_MacOSX_SetScheduler(SchedPriority);
#else
LOG_FATAL(LOGF_Sys, "scheduler priority setting not supported");
#endif
diff --git a/sys_macosx.c b/sys_macosx.c
index 33da60d..bd405f1 100644
--- a/sys_macosx.c
+++ b/sys_macosx.c
@@ -42,7 +42,12 @@
#include <stdio.h>
#include <signal.h>
+#include <mach/mach.h>
+#include <mach/mach_time.h>
+#include <pthread.h>
+
#include "sys_macosx.h"
+#include "conf.h"
#include "localp.h"
#include "sched.h"
#include "logging.h"
@@ -85,6 +90,8 @@ static struct timeval Tdrift;
/* minimum resolution of current_frequency */
#define FREQUENCY_RES (1.0e-9)
+#define NANOS_PER_MSEC (1000000ULL)
+
/* ================================================== */
static void
@@ -335,6 +342,53 @@ drift_removal_timeout(SCH_ArbitraryArgument not_used)
}
/* ================================================== */
+/*
+ Give chronyd real time priority so that time critical calculations
+ are not pre-empted by the kernel.
+*/
+
+static int
+set_realtime(void)
+{
+ /* https://developer.apple.com/library/ios/technotes/tn2169/_index.html */
+
+ mach_timebase_info_data_t timebase_info;
+ double clock2abs;
+ thread_time_constraint_policy_data_t policy;
+ int kr;
+
+ mach_timebase_info(&timebase_info);
+ clock2abs = ((double)timebase_info.denom / (double)timebase_info.numer) *
NANOS_PER_MSEC;
+
+ policy.period = 0;
+ policy.computation = (uint32_t)(5 * clock2abs); /* 5 ms of work */
+ policy.constraint = (uint32_t)(10 * clock2abs);
+ policy.preemptible = 0;
+
+ kr = thread_policy_set(
+ pthread_mach_thread_np(pthread_self()),
+ THREAD_TIME_CONSTRAINT_POLICY,
+ (thread_policy_t)&policy,
+ THREAD_TIME_CONSTRAINT_POLICY_COUNT);
+
+ if (kr != KERN_SUCCESS) {
+ LOG(LOGS_WARN, LOGF_SysMacOSX, "Cannot set real-time priority: %d", kr);
+ return -1;
+ }
+ return 0;
+}
+
+/* ================================================== */
+
+void
+SYS_MacOSX_SetScheduler(int SchedPriority)
+{
+ if (SchedPriority) {
+ set_realtime();
+ }
+}
+
+/* ================================================== */
void
SYS_MacOSX_Initialise(void)
diff --git a/sys_macosx.h b/sys_macosx.h
index b579415..707700d 100644
--- a/sys_macosx.h
+++ b/sys_macosx.h
@@ -30,8 +30,8 @@
#ifndef GOT_SYS_MACOSX_H
#define GOT_SYS_MACOSX_H
+void SYS_MacOSX_SetScheduler(int SchedPriority);
void SYS_MacOSX_Initialise(void);
-
void SYS_MacOSX_Finalise(void);
#endif
--
2.3.2 (Apple Git-55)
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