genirq/timings: Add infrastructure for estimating the next interrupt arrival time

An interrupt behaves with a burst of activity with periodic interval of time
followed by one or two peaks of longer interval.

As the time intervals are periodic, statistically speaking they follow a normal
distribution and each interrupts can be tracked individually.

Add a mechanism to compute the statistics on all interrupts, except the
timers which are deterministic from a prediction point of view, as their
expiry time is known.

The goal is to extract the periodicity for each interrupt, with the last
timestamp and sum them, so the next event can be predicted to a certain
extent.

Taking the earliest prediction gives the expected wakeup on the system
(assuming a timer won't expire before).

Signed-off-by: Daniel Lezcano <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: "Rafael J . Wysocki" <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]

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