diff options
Diffstat (limited to 'usr.sbin/xntpd/util/precision.c')
| -rw-r--r-- | usr.sbin/xntpd/util/precision.c | 150 |
1 files changed, 0 insertions, 150 deletions
diff --git a/usr.sbin/xntpd/util/precision.c b/usr.sbin/xntpd/util/precision.c deleted file mode 100644 index 64fe336fe662..000000000000 --- a/usr.sbin/xntpd/util/precision.c +++ /dev/null @@ -1,150 +0,0 @@ -#include <sys/types.h> -#include <sys/time.h> -#include "ntp_unixtime.h" - -#define DEFAULT_SYS_PRECISION -99 - -int default_get_resolution(); -int default_get_precision(); - -int -main() { - printf("log2(resolution) = %d, log2(precision) = %d\n", - default_get_resolution(), - default_get_precision()); - return 0; -} - -/* Find the resolution of the system clock by watching how the current time - * changes as we read it repeatedly. - * - * struct timeval is only good to 1us, which may cause problems as machines - * get faster, but until then the logic goes: - * - * If a machine has resolution (i.e. accurate timing info) > 1us, then it will - * probably use the "unused" low order bits as a counter (to force time to be - * a strictly increaing variable), incrementing it each time any process - * requests the time [[ or maybe time will stand still ? ]]. - * - * SO: the logic goes: - * - * IF the difference from the last time is "small" (< MINSTEP) - * THEN this machine is "counting" with the low order bits - * ELIF this is not the first time round the loop - * THEN this machine *WAS* counting, and has now stepped - * ELSE this machine has resolution < time to read clock - * - * SO: if it exits on the first loop, assume "full accuracy" (1us) - * otherwise, take the log2(observered difference, rounded UP) - * - * MINLOOPS > 1 ensures that even if there is a STEP between the initial call - * and the first loop, it doesn't stop too early. - * Making it even greater allows MINSTEP to be reduced, assuming that the - * chance of MINSTEP-1 other processes getting in and calling gettimeofday - * between this processes's calls. - * Reducing MINSTEP may be necessary as this sets an upper bound for the time - * to actually call gettimeofday. - */ - -#define DUSECS 1000000 -#define HUSECS (1024 * 1024) -#define MINSTEP 5 /* some systems increment uS on each call */ - /* Don't use "1" as some *other* process may read too*/ - /*We assume no system actually *ANSWERS* in this time*/ -#define MAXSTEP 20000 /* maximum clock increment (us) */ -#define MINLOOPS 5 /* minimum number of step samples */ -#define MAXLOOPS HUSECS /* Assume precision < .1s ! */ - -int default_get_resolution() -{ - struct timeval tp; - struct timezone tzp; - long last; - int i; - long diff; - long val; - int minsteps = MINLOOPS; /* need at least this many steps */ - - gettimeofday(&tp, &tzp); - last = tp.tv_usec; - for (i = - --minsteps; i< MAXLOOPS; i++) { - gettimeofday(&tp, &tzp); - diff = tp.tv_usec - last; - if (diff < 0) diff += DUSECS; - if (diff > MINSTEP) if (minsteps-- <= 0) break; - last = tp.tv_usec; - } - - printf("resolution = %ld usec after %d loop%s\n", - diff, i, (i==1) ? "" : "s"); - - diff = (diff *3)/2; - if (i >= MAXLOOPS) { - printf( - " (Boy this machine is fast ! %d loops without a step)\n", - MAXLOOPS); - diff = 1; /* No STEP, so FAST machine */ - } - if (i == 0) { - printf( -" (The resolution is less than the time to read the clock -- Assume 1us)\n"); - diff = 1; /* time to read clock >= resolution */ - } - for (i=0, val=HUSECS; val>0; i--, val >>= 1) if (diff >= val) return i; - printf(" (Oh dear -- that wasn't expected ! I'll guess !)\n"); - return DEFAULT_SYS_PRECISION /* Something's BUST, so lie ! */; -} - -/* ===== Rest of this code lifted straight from xntpd/ntp_proto.c ! ===== */ - -/* - * This routine calculates the differences between successive calls to - * gettimeofday(). If a difference is less than zero, the us field - * has rolled over to the next second, so we add a second in us. If - * the difference is greater than zero and less than MINSTEP, the - * clock has been advanced by a small amount to avoid standing still. - * If the clock has advanced by a greater amount, then a timer interrupt - * has occurred and this amount represents the precision of the clock. - * In order to guard against spurious values, which could occur if we - * happen to hit a fat interrupt, we do this for MINLOOPS times and - * keep the minimum value obtained. - */ -int default_get_precision() -{ - struct timeval tp; - struct timezone tzp; - long last; - int i; - long diff; - long val; - long usec; - - usec = 0; - val = MAXSTEP; - GETTIMEOFDAY(&tp, &tzp); - last = tp.tv_usec; - for (i = 0; i < MINLOOPS && usec < HUSECS;) { - GETTIMEOFDAY(&tp, &tzp); - diff = tp.tv_usec - last; - last = tp.tv_usec; - if (diff < 0) - diff += DUSECS; - usec += diff; - if (diff > MINSTEP) { - i++; - if (diff < val) - val = diff; - } - } - printf("precision = %ld usec after %d loop%s\n", - val, i, (i == 1) ? "" : "s"); - if (usec >= HUSECS) { - printf(" (Boy this machine is fast ! usec was %ld)\n", - usec); - val = MINSTEP; /* val <= MINSTEP; fast machine */ - } - diff = HUSECS; - for (i = 0; diff > val; i--) - diff >>= 1; - return (i); -} |