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.
