driver-api/thermal/cpu-idle-cooling.rst

1 .. SPDX-License-Identifier: GPL-2.0
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26 budget lower than the requested one and under-utilize the CPU, thus
27 losing performance. In other words, one OPP under-utilizes the CPU
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37 decrease. Acting on the idle state duration or the idle cycle
47 At a specific OPP, we can assume that injecting idle cycle on all CPUs
58 ---------------
61 idle state for a specified time each control cycle, it provides
71 or decreased by modulating the duty cycle of the idle injection.
78      |-------                         -------
81      <------>
82        idle  <---------------------->
85       <----------------------------->
86               duty cycle 25%
90 the duty cycle percentage. When no mitigation is happening the cooling
91 device state is zero, meaning the duty cycle is 0%.
94 starting state is selected. With a fixed idle duration and the duty
95 cycle (aka the cooling device state), the running duration can be
98 The governor will change the cooling device state thus the duty cycle
106      |-------                 -------
109      <------>
110        idle  <-------------->
113       <--------------------->
114           duty cycle 33%
120      |-------         -------
123      <------>
124        idle  <------>
127       <------------->
128        duty cycle 50%
132 - It is less than or equal to the latency we tolerate when the
137 - It is greater than the idle state’s target residency we want to go
141 --------------------
169  Tidle = Trunning x ((P(opp)running / P(opp)target) - 1)
175  Trunning = Tidle / ((P(opp)running / P(opp)target) - 1)
198  Trunning = (Tidle - Twakeup ) x
199 		(((P(opp)dyn + P(opp)static ) - P(opp)target) / P(opp)target )