1CPUPOWER-IDLE-INFO(1) cpupower Manual CPUPOWER-IDLE-INFO(1)
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6 cpupower-idle-info - Utility to retrieve cpu idle kernel information
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9 cpupower [ -c cpulist ] idle-info [options]
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12 A tool which prints out per cpu idle information helpful to developers
13 and interested users.
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16 -f --silent
17 Only print a summary of all available C-states in the system.
18 -e --proc
20 deprecated. Prints out idle information in old /proc/acpi/pro‐
21 cessor/*/power format. This interface has been removed from the
22 kernel for quite some time, do not let further code depend on
23 this option, best do not use it.
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27 CPU sleep state statistics and descriptions are retrieved from sysfs
28 files, exported by the cpuidle kernel subsystem. The kernel only
29 updates these statistics when it enters or leaves an idle state, there‐
30 fore on a very idle or a very busy system, these statistics may not be
31 accurate. They still provide a good overview about the usage and avail‐
32 ability of processor sleep states on the platform.
33 Be aware that the sleep states as exported by the hardware or BIOS and
35 used by the Linux kernel may not exactly reflect the capabilities of
36 the processor. This often is the case on the X86 architecture when the
37 acpi_idle driver is used. It is also possible that the hardware over‐
38 rules the kernel requests, due to internal activity monitors or other
39 reasons. On recent X86 platforms it is often possible to read out
40 hardware registers which monitor the duration of sleep states the pro‐
41 cessor resided in. The cpupower monitor tool (cpupower-monitor(1)) can
42 be used to show real sleep state residencies. Please refer to the
43 architecture specific description section below.
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47 X86
48 POLL idle state
49 If cpuidle is active, X86 platforms have one special idle state. The
51 POLL idle state is not a real idle state, it does not save any power.
52 Instead, a busy-loop is executed doing nothing for a short period of
53 time. This state is used if the kernel knows that work has to be pro‐
54 cessed very soon and entering any real hardware idle state may result
55 in a slight performance penalty.
56 There exist two different cpuidle drivers on the X86 architecture plat‐
58 form:
59 "acpi_idle" cpuidle driver
61 The acpi_idle cpuidle driver retrieves available sleep states
63 (C-states) from the ACPI BIOS tables (from the _CST ACPI function on
64 recent platforms or from the FADT BIOS table on older ones). The C1
65 state is not retrieved from ACPI tables. If the C1 state is entered,
66 the kernel will call the hlt instruction (or mwait on Intel).
67 "intel_idle" cpuidle driver
69 In kernel 2.6.36 the intel_idle driver was introduced. It only serves
71 recent Intel CPUs (Nehalem, Westmere, Sandybridge, Atoms or newer). On
72 older Intel CPUs the acpi_idle driver is still used (if the BIOS pro‐
73 vides C-state ACPI tables). The intel_idle driver knows the sleep
74 state capabilities of the processor and ignores ACPI BIOS exported pro‐
75 cessor sleep states tables.
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79 By default only values of core zero are displayed. How to display set‐
80 tings of other cores is described in the cpupower(1) manpage in the
81 --cpu option section.
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84 http://www.acpi.info/spec.htm
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87 /sys/devices/system/cpu/cpu*/cpuidle/state*
88 /sys/devices/system/cpu/cpuidle/*
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91 Thomas Renninger <trenn@suse.de>
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94 cpupower(1), cpupower-monitor(1), cpupower-info(1), cpupower-set(1),
95 cpupower-idle-set(1)
96 0.1 CPUPOWER-IDLE-INFO(1)