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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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53
sys_macosx.c
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@@ -42,6 +42,10 @@
#include <stdio.h>
#include <signal.h>
#include <mach/mach.h>
#include <mach/mach_time.h>
#include <pthread.h>
#include "sys_macosx.h"
#include "localp.h"
#include "sched.h"
@@ -85,6 +89,8 @@ static struct timeval Tdrift;
/* minimum resolution of current_frequency */
#define FREQUENCY_RES (1.0e-9)
#define NANOS_PER_MSEC (1000000ULL)
/* ================================================== */
static void
@@ -334,6 +340,53 @@ drift_removal_timeout(SCH_ArbitraryArgument not_used)
drift_removal_id = SCH_AddTimeoutByDelay(drift_removal_interval, drift_removal_timeout, NULL);
}
/* ================================================== */
/*
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