static inline void update_time(void) {
	static uint32_t count = 0;
	++count;

	/* now_real = initial realtime + monotonic shift */
	uint64_t curr_monotonic = gettime_nano(CLOCK_MONOTONIC);
	now_real = ns2sec(init_real + curr_monotonic - init_monotonic);
	now_monotonic = ns2sec(curr_monotonic);

	if (count >= ADJTIME_PERIOD) {
		count = 0;

		/* compare the fresh realtime and the old one, if the offset is
		 * in safe range, re-init the init real/monotonic time */
		double offset = fabs(ns2sec(gettime_nano(CLOCK_REALTIME)) - now_real);
		if (offset > ADJTIME_OFFSET_MAX) {
			LogSysWarn("time offset too large %.3f/%.3f sec, won't adjust it",
					offset, ADJTIME_OFFSET_MAX);
			return;
		}
		else if (offset >= ADJTIME_OFFSET_MIN) {
			init_time();
			/* update adjusted now time */
			now_real = ns2sec(init_real);
			now_monotonic = ns2sec(init_monotonic);
#if ADJTIME_DEBUG
			LogSysDebug("time offset %.3f sec adjusted", offset);
#endif
		}
	}
}