3  * Timer events oriented CPU idle governor
20  * wakeups from idle states.  Moreover, information about what happened in the
22  * idle state with target residency within the (known) time till the closest
24  * the upcoming CPU idle period and, if not, then which of the shallower idle
28  * which can be covered by taking a few most recent idle time intervals of the
30  * consider idle duration values greater than the sleep length, because the
34  * Thus this governor estimates whether or not the prospective idle duration of
36  * an idle state for it accordingly.
40  * idle states provided by the %CPUIdle driver in the ascending order.  That is,
42  * the second idle state (idle state 1), the second bin spans from the target
43  * residency of idle state 1 up to, but not including, the target residency of
44  * idle state 2, the third bin spans from the target residency of idle state 2
45  * up to, but not including, the target residency of idle state 3 and so on.
46  * The last bin spans from the target residency of the deepest idle state
50  * They are updated every time before selecting an idle state for the given CPU
54  * sleep length and the idle duration measured after CPU wakeup fall into the
57  * situations in which the measured idle duration is so much shorter than the
58  * sleep length that the bin it falls into corresponds to an idle state
66  * In order to select an idle state for a CPU, the governor takes the following
70  * 1. Find the deepest CPU idle state whose target residency does not exceed
71  *    the current sleep length (the candidate idle state) and compute 3 sums as
75  *      and all of the deeper idle states (it represents the cases in which the
76  *      CPU was idle long enough to avoid being intercepted if the sleep length
79  *    - The sum of the "intercepts" metrics for all of the idle states shallower
81  *      idle long enough to avoid being intercepted if the sleep length had been
84  *    - The sum of the numbers of recent intercepts for all of the idle states
89  *    for an alternative idle state to select.
91  *    - Traverse the idle states shallower than the candidate one in the
95  *      of the numbers of recent intercepts over all of the idle states between
103  *      not exceeded the idle duration in over a half of the relevant cases),
104  *      select the given idle state instead of the candidate one.
111  * scenarios for the CPU which should result in two different approaches to idle
117  * When the CPU is utilized while going into idle, more likely than not it will
118  * be woken up to do more work soon and so a shallower idle state should be
121  * available idle state should be preferred to take advantage of the power
129  * Before selecting the next idle state, the governor compares the current CPU
131  * TEO metrics mechanism. If it's above, the closest shallower idle state will
165  * Number of the most recent idle duration values to take into consideration for
184  * @time_span_ns: Time between idle state selection and post-wakeup update.
186  * @state_bins: Idle state data bins for this CPU.
238 		 * enough to the closest timer event expected at the idle state  in teo_update()
247 		 * (saved) time till the next timer event and the measured idle  in teo_update()
269 	 * find the bins that the sleep length and the measured idle duration  in teo_update()
317 	 * If the measured idle duration falls into the same bin as the sleep  in teo_update()
320 	 * the measured idle duration.  in teo_update()
342  * teo_find_shallower_state - Find shallower idle state matching given duration.
345  * @state_idx: Index of the capping idle state.
346  * @duration_ns: Idle duration value to match.
368  * teo_select - Selects the next idle state to enter.
446 		 * Update the sums of idle state mertics for all of the states  in teo_select()
478 		 * Only one idle state is enabled, so use it, but do not  in teo_select()
489 	 * If the sum of the intercepts metric for all of the idle states  in teo_select()
495 	 * account, a shallower idle state is likely to be a better choice.  in teo_select()
503 		 * Look for the deepest idle state whose target residency had  in teo_select()
504 		 * not exceeded the idle duration in over a half of the relevant  in teo_select()
558 	 * idle state shallower than the current candidate one.  in teo_select()
616 	 * one or the expected idle duration is shorter than the tick period  in teo_select()
649 	 * nets, assume that the CPU might have been idle for the entire sleep  in teo_reflect()