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sys: add drift removal to Mac OS X driver

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The darwin kernel implementation of adjtime() does not require the
adjustment to be aligned to a tickadj boundary, and we can apply
adjustments to the nearest microsecond. Rounding is accounted for by
adding any rounding errors back into the offset.
This commit is contained in:
Bryan Christianson 2015-07-30 09:50:26 +12:00 committed by Miroslav Lichvar
parent 0bcd10560a
commit abb56bded2
1 changed files with 38 additions and 43 deletions
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81
sys_macosx.c
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@ -44,6 +44,7 @@
#include "sys_macosx.h"
#include "localp.h"
#include "sched.h"
#include "logging.h"
#include "util.h"
@ -69,11 +70,6 @@ static double current_freq;
static double adjustment_requested;
/* Kernel parameters to calculate adjtime error. */
static int kern_tickadj;
static long kern_bigadj;
/* ================================================== */
static void
@ -114,8 +110,6 @@ start_adjust(void)
struct timeval T1;
double elapsed, accrued_error;
double adjust_required;
struct timeval exact_newadj;
long delta, tickdelta;
double rounding_error;
double old_adjust_remaining;
@ -129,24 +123,9 @@ start_adjust(void)
adjust_required = - (accrued_error + offset_register);
UTI_DoubleToTimeval(adjust_required, &exact_newadj);
/* At this point, we need to round the required adjustment the
same way the kernel does. */
delta = exact_newadj.tv_sec * 1000000 + exact_newadj.tv_usec;
if (delta > kern_bigadj || delta < -kern_bigadj)
tickdelta = 10 * kern_tickadj;
else
tickdelta = kern_tickadj;
if (delta % tickdelta)
delta = delta / tickdelta * tickdelta;
newadj.tv_sec = 0;
newadj.tv_usec = (int)delta;
UTI_NormaliseTimeval(&newadj);
/* Add rounding error back onto offset register. */
UTI_DiffTimevalsToDouble(&rounding_error, &newadj, &exact_newadj);
UTI_DoubleToTimeval(adjust_required, &newadj);
UTI_TimevalToDouble(&newadj, &adjustment_requested);
rounding_error = adjust_required - adjustment_requested;
if (adjtime(&newadj, &oldadj) < 0) {
LOG_FATAL(LOGF_SysMacOSX, "adjtime() failed");
@ -157,7 +136,6 @@ start_adjust(void)
offset_register = rounding_error - old_adjust_remaining;
T0 = T1;
UTI_TimevalToDouble(&newadj, &adjustment_requested);
}
/* ================================================== */
@ -272,26 +250,35 @@ get_offset_correction(struct timeval *raw,
/* ================================================== */
/* Interval in seconds between adjustments to cancel systematic drift */
#define DRIFT_REMOVAL_INTERVAL (1.0)
static int drift_removal_running = 0;
static SCH_TimeoutID drift_removal_id;
/* ================================================== */
/* This is the timer callback routine which is called periodically to
invoke a time adjustment to take out the machine's drift.
Otherwise, times reported through this software (e.g. by running
ntpdate from another machine) show the machine being correct (since
they correct for drift build-up), but any program on this machine
that reads the system time will be given an erroneous value, the
degree of error depending on how long it is since
get_offset_correction was last called. */
static void
drift_removal_timeout(SCH_ArbitraryArgument not_used)
{
stop_adjust();
start_adjust();
drift_removal_id = SCH_AddTimeoutByDelay(DRIFT_REMOVAL_INTERVAL, drift_removal_timeout, NULL);
}
/* ================================================== */
void
SYS_MacOSX_Initialise(void)
{
int result;
size_t len;
struct clockinfo clockinfo;
int mib[2];
mib[0] = CTL_KERN;
mib[1] = KERN_CLOCKRATE;
len = sizeof(clockinfo);
result = sysctl(mib, 2, &clockinfo, &len, NULL, 0);
if(result < 0) {
LOG_FATAL(LOGF_SysMacOSX, "Cannot read clockinfo");
}
kern_tickadj = clockinfo.tickadj;
kern_bigadj = clockinfo.tick;
clock_initialise();
lcl_RegisterSystemDrivers(read_frequency, set_frequency,
@ -299,6 +286,10 @@ SYS_MacOSX_Initialise(void)
get_offset_correction,
NULL /* set_leap */,
NULL /* set_sync_status */);
drift_removal_id = SCH_AddTimeoutByDelay(DRIFT_REMOVAL_INTERVAL, drift_removal_timeout, NULL);
drift_removal_running = 1;
}
/* ================================================== */
@ -306,6 +297,10 @@ SYS_MacOSX_Initialise(void)
void
SYS_MacOSX_Finalise(void)
{
if (drift_removal_running) {
SCH_RemoveTimeout(drift_removal_id);
}
clock_finalise();
}