1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 ===========================
5 Power Management Strategies
6 ===========================
7
8 :Copyright: |copy| 2017 Intel Corporation
9
10 :Author: Rafael J. Wysocki <rafael.j.wysocki@in
11
12
13 The Linux kernel supports two major high-level
14
15 One of them is based on using global low-power
16 which user space code cannot be executed and t
17 significantly reduced, referred to as :doc:`sl
18 kernel puts the system into one of these state
19 and the system stays in it until a special sig
20 designated devices, triggering a transition to
21 user space code can run. Because sleep states
22 is affected by the state changes, this strateg
23 :doc:`system-wide power management <system-wid
24
25 The other strategy, referred to as the :doc:`w
26 <working-state>`, is based on adjusting the po
27 components of the system, as needed, in the wo
28 this strategy is in use, the working state of
29 correspond to any particular physical configur
30 a metastate covering a range of different powe
31 the individual components of it can be either
32 ``inactive`` (idle). If they are active, they
33 allowing them to process data and to be access
34 are inactive, ideally, they should be in low-p
35 be accessible.
36
37 If all of the system components are active, th
38 "runtime active" and that situation typically
39 draw (or maximum energy usage) of it. If all
40 as a whole is regarded as "runtime idle" which
41 state from the physical system configuration a
42 then it takes much less time and effort to sta
43 for the same system in a sleep state. However
44 back to the working state can only be started
45 typically the system can spend much more time
46 runtime idle in one go. For this reason, syst
47 sleep states than when they are runtime idle m
48
49 Moreover, the two power management strategies
50 Namely, if the user indicates that the system
51 for example by closing its lid (if the system
52 go into a sleep state at that point. On the o
53 away from the laptop keyboard, it probably sho
54 use the working-state power management in case
55 may come back to it at any time and then may w
56 accessible.
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