On Wed, Jan 20, 2016 at 05:00:33PM +0100, Daniel Lezcano wrote:

+static void sched_irq_timing_handler(unsigned int irq, ktime_t timestamp, void *dev_id)
+{
+	u32 diff;
+	unsigned int cpu = raw_smp_processor_id();
+	struct wakeup *w = per_cpu(wakeups[irq], cpu);
+
+	/*
+	 * It is the first time the interrupt occurs of the series, we
+	 * can't do any stats as we don't have an interval, just store
+	 * the timestamp and exit.
+	 */
+	if (ktime_equal(w->timestamp, ktime_set(0, 0))) {
+		w->timestamp = timestamp;
+		return;
+	}
+
+	/*
+	 * Microsec resolution is enough for our purpose.
+	 */

It is also a friggin pointless /1000. The cpuidle code also loves to do
this, and its silly, u64 add/sub are _way_ cheaper than u64 / 1000.

+	diff = ktime_us_delta(timestamp, w->timestamp);
+	w->timestamp = timestamp;
+
+	/*
+	 * There is no point attempting predictions on interrupts more
+	 * than ~1 second apart. This has no benefit for sleep state
+	 * selection and increases the risk of overflowing our variance
+	 * computation. Reset all stats in that case.
+	 */
+	if (diff > (1 << 20)) {
+		stats_reset(&w->stats);
+		return;
+	}
+
+	stats_add(&w->stats, diff);
+}
+
+static ktime_t next_irq_event(void)
+{
+	unsigned int irq, cpu = raw_smp_processor_id();
+	ktime_t diff, next, min = ktime_set(KTIME_SEC_MAX, 0);
+	ktime_t now = ktime_get();

Why !?! do we care about NTP correct timestamps?

ktime_get() can be horrendously slow, don't use it for statistics.

+		next = ktime_add_us(w->timestamp, stats_mean(&w->stats));
+	s64 next_timer = ktime_to_us(tick_nohz_get_sleep_length());
+	s64 next_irq = ktime_to_us(next_irq_event());

more nonsense, just say no.