static void led_activity_function()

in trigger/ledtrig-activity.c [33:152]

• 65 lines of code
• 14 McCabe index (conditional complexity)

static void led_activity_function(struct timer_list *t)
{
	struct activity_data *activity_data = from_timer(activity_data, t,
							 timer);
	struct led_classdev *led_cdev = activity_data->led_cdev;
	unsigned int target;
	unsigned int usage;
	int delay;
	u64 curr_used;
	u64 curr_boot;
	s32 diff_used;
	s32 diff_boot;
	int cpus;
	int i;

	if (test_and_clear_bit(LED_BLINK_BRIGHTNESS_CHANGE, &led_cdev->work_flags))
		led_cdev->blink_brightness = led_cdev->new_blink_brightness;

	if (unlikely(panic_detected)) {
		/* full brightness in case of panic */
		led_set_brightness_nosleep(led_cdev, led_cdev->blink_brightness);
		return;
	}

	cpus = 0;
	curr_used = 0;

	for_each_possible_cpu(i) {
		struct kernel_cpustat kcpustat;

		kcpustat_cpu_fetch(&kcpustat, i);

		curr_used += kcpustat.cpustat[CPUTIME_USER]
			  +  kcpustat.cpustat[CPUTIME_NICE]
			  +  kcpustat.cpustat[CPUTIME_SYSTEM]
			  +  kcpustat.cpustat[CPUTIME_SOFTIRQ]
			  +  kcpustat.cpustat[CPUTIME_IRQ];
		cpus++;
	}

	/* We come here every 100ms in the worst case, so that's 100M ns of
	 * cumulated time. By dividing by 2^16, we get the time resolution
	 * down to 16us, ensuring we won't overflow 32-bit computations below
	 * even up to 3k CPUs, while keeping divides cheap on smaller systems.
	 */
	curr_boot = ktime_get_boottime_ns() * cpus;
	diff_boot = (curr_boot - activity_data->last_boot) >> 16;
	diff_used = (curr_used - activity_data->last_used) >> 16;
	activity_data->last_boot = curr_boot;
	activity_data->last_used = curr_used;

	if (diff_boot <= 0 || diff_used < 0)
		usage = 0;
	else if (diff_used >= diff_boot)
		usage = 100;
	else
		usage = 100 * diff_used / diff_boot;

	/*
	 * Now we know the total boot_time multiplied by the number of CPUs, and
	 * the total idle+wait time for all CPUs. We'll compare how they evolved
	 * since last call. The % of overall CPU usage is :
	 *
	 *      1 - delta_idle / delta_boot
	 *
	 * What we want is that when the CPU usage is zero, the LED must blink
	 * slowly with very faint flashes that are detectable but not disturbing
	 * (typically 10ms every second, or 10ms ON, 990ms OFF). Then we want
	 * blinking frequency to increase up to the point where the load is
	 * enough to saturate one core in multi-core systems or 50% in single
	 * core systems. At this point it should reach 10 Hz with a 10/90 duty
	 * cycle (10ms ON, 90ms OFF). After this point, the blinking frequency
	 * remains stable (10 Hz) and only the duty cycle increases to report
	 * the activity, up to the point where we have 90ms ON, 10ms OFF when
	 * all cores are saturated. It's important that the LED never stays in
	 * a steady state so that it's easy to distinguish an idle or saturated
	 * machine from a hung one.
	 *
	 * This gives us :
	 *   - a target CPU usage of min(50%, 100%/#CPU) for a 10% duty cycle
	 *     (10ms ON, 90ms OFF)
	 *   - below target :
	 *      ON_ms  = 10
	 *      OFF_ms = 90 + (1 - usage/target) * 900
	 *   - above target :
	 *      ON_ms  = 10 + (usage-target)/(100%-target) * 80
	 *      OFF_ms = 90 - (usage-target)/(100%-target) * 80
	 *
	 * In order to keep a good responsiveness, we cap the sleep time to
	 * 100 ms and keep track of the sleep time left. This allows us to
	 * quickly change it if needed.
	 */

	activity_data->time_left -= 100;
	if (activity_data->time_left <= 0) {
		activity_data->time_left = 0;
		activity_data->state = !activity_data->state;
		led_set_brightness_nosleep(led_cdev,
			(activity_data->state ^ activity_data->invert) ?
			led_cdev->blink_brightness : LED_OFF);
	}

	target = (cpus > 1) ? (100 / cpus) : 50;

	if (usage < target)
		delay = activity_data->state ?
			10 :                        /* ON  */
			990 - 900 * usage / target; /* OFF */
	else
		delay = activity_data->state ?
			10 + 80 * (usage - target) / (100 - target) : /* ON  */
			90 - 80 * (usage - target) / (100 - target);  /* OFF */


	if (!activity_data->time_left || delay <= activity_data->time_left)
		activity_data->time_left = delay;

	delay = min_t(int, activity_data->time_left, 100);
	mod_timer(&activity_data->timer, jiffies + msecs_to_jiffies(delay));
}