1CPUPOWER-IDLE-INFO(1)           cpupower Manual          CPUPOWER-IDLE-INFO(1)
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NAME

6       cpupower-idle-info - Utility to retrieve cpu idle kernel information
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SYNTAX

9       cpupower [ -c cpulist ] idle-info [options]
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DESCRIPTION

12       A  tool which prints out per cpu idle information helpful to developers
13       and interested users.
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OPTIONS

16       -f --silent
17              Only print a summary of all available C-states in the system.
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19       -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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IDLE-INFO DESCRIPTIONS

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.
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34       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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IDLE-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS

47   X86
48       POLL idle state
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50       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.
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57       There exist two different cpuidle drivers on the X86 architecture plat‐
58       form:
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60       "acpi_idle" cpuidle driver
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62       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).
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68       "intel_idle" cpuidle driver
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70       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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REMARKS

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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REFERENCES

84       http://www.acpi.info/spec.htm
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FILES

87       /sys/devices/system/cpu/cpu*/cpuidle/state*
88       /sys/devices/system/cpu/cpuidle/*
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AUTHORS

91       Thomas Renninger <trenn@suse.de>
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SEE ALSO

94       cpupower(1),  cpupower-monitor(1),  cpupower-info(1),  cpupower-set(1),
95       cpupower-idle-set(1)
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99                                      0.1                CPUPOWER-IDLE-INFO(1)
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