init/calibrate.c

Source file repositories/reference/linux-study-clean/init/calibrate.c

File Facts

System
Linux kernel
Corpus path
init/calibrate.c
Extension
.c
Size
8827 bytes
Lines
320
Domain
Core OS
Bucket
Boot And Init
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

while (time_before_eq(jiffies, start_jiffies + 1)) {
			pre_start = start;
			read_current_timer(&start);
		}
		read_current_timer(&post_start);

		pre_end = 0;
		end = post_start;
		while (time_before_eq(jiffies, start_jiffies + 1 +
					       DELAY_CALIBRATION_TICKS)) {
			pre_end = end;
			read_current_timer(&end);
		}
		read_current_timer(&post_end);

		timer_rate_max = (post_end - pre_start) /
					DELAY_CALIBRATION_TICKS;
		timer_rate_min = (pre_end - post_start) /
					DELAY_CALIBRATION_TICKS;

		/*
		 * If the upper limit and lower limit of the timer_rate is
		 * >= 12.5% apart, redo calibration.
		 */
		if (start >= post_end)
			printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
					"timer_rate as we had a TSC wrap around"
					" start=%lu >=post_end=%lu\n",
				start, post_end);
		if (start < post_end && pre_start != 0 && pre_end != 0 &&
		    (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
			good_timer_count++;
			good_timer_sum += timer_rate_max;
			measured_times[i] = timer_rate_max;
			if (max < 0 || timer_rate_max > measured_times[max])
				max = i;
			if (min < 0 || timer_rate_max < measured_times[min])
				min = i;
		} else
			measured_times[i] = 0;

	}

	/*
	 * Find the maximum & minimum - if they differ too much throw out the
	 * one with the largest difference from the mean and try again...
	 */
	while (good_timer_count > 1) {
		unsigned long estimate;
		unsigned long maxdiff;

		/* compute the estimate */
		estimate = (good_timer_sum/good_timer_count);
		maxdiff = estimate >> 3;

		/* if range is within 12% let's take it */
		if ((measured_times[max] - measured_times[min]) < maxdiff)
			return estimate;

		/* ok - drop the worse value and try again... */
		good_timer_sum = 0;
		good_timer_count = 0;
		if ((measured_times[max] - estimate) <
				(estimate - measured_times[min])) {
			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
					"min bogoMips estimate %d = %lu\n",
				min, measured_times[min]);
			measured_times[min] = 0;
			min = max;
		} else {
			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
					"max bogoMips estimate %d = %lu\n",
				max, measured_times[max]);
			measured_times[max] = 0;
			max = min;
		}

		for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
			if (measured_times[i] == 0)
				continue;
			good_timer_count++;
			good_timer_sum += measured_times[i];
			if (measured_times[i] < measured_times[min])
				min = i;
			if (measured_times[i] > measured_times[max])
				max = i;
		}

	}

Annotation

Implementation Notes