2024-09-09 08:52:07 +00:00
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.TH "CPUPOWER-IDLE-INFO" "1" "0.1" "" "cpupower Manual"
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.SH "NAME"
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.LP
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cpupower idle\-info \- Utility to retrieve cpu idle kernel information
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.SH "SYNTAX"
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.LP
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cpupower [ \-c cpulist ] idle\-info [\fIoptions\fP]
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.SH "DESCRIPTION"
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.LP
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A tool which prints out per cpu idle information helpful to developers and interested users.
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.SH "OPTIONS"
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.LP
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.TP
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\fB\-f\fR \fB\-\-silent\fR
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Only print a summary of all available C-states in the system.
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.TP
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\fB\-e\fR \fB\-\-proc\fR
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deprecated.
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Prints out idle information in old /proc/acpi/processor/*/power format. This
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interface has been removed from the kernel for quite some time, do not let
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further code depend on this option, best do not use it.
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.SH IDLE\-INFO DESCRIPTIONS
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CPU sleep state statistics and descriptions are retrieved from sysfs files,
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exported by the cpuidle kernel subsystem. The kernel only updates these
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statistics when it enters or leaves an idle state, therefore on a very idle or
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a very busy system, these statistics may not be accurate. They still provide a
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good overview about the usage and availability of processor sleep states on
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the platform.
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Be aware that the sleep states as exported by the hardware or BIOS and used by
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the Linux kernel may not exactly reflect the capabilities of the
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processor. This often is the case on the X86 architecture when the acpi_idle
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driver is used. It is also possible that the hardware overrules the kernel
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requests, due to internal activity monitors or other reasons.
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On recent X86 platforms it is often possible to read out hardware registers
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which monitor the duration of sleep states the processor resided in. The
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cpupower monitor tool (cpupower\-monitor(1)) can be used to show real sleep
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state residencies. Please refer to the architecture specific description
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section below.
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.SH IDLE\-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS
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.SS "X86"
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POLL idle state
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If cpuidle is active, X86 platforms have one special idle state.
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The POLL idle state is not a real idle state, it does not save any
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power. Instead, a busy\-loop is executed doing nothing for a short period of
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time. This state is used if the kernel knows that work has to be processed
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very soon and entering any real hardware idle state may result in a slight
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performance penalty.
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There exist two different cpuidle drivers on the X86 architecture platform:
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"acpi_idle" cpuidle driver
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The acpi_idle cpuidle driver retrieves available sleep states (C\-states) from
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the ACPI BIOS tables (from the _CST ACPI function on recent platforms or from
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the FADT BIOS table on older ones).
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The C1 state is not retrieved from ACPI tables. If the C1 state is entered,
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the kernel will call the hlt instruction (or mwait on Intel).
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"intel_idle" cpuidle driver
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In kernel 2.6.36 the intel_idle driver was introduced.
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It only serves recent Intel CPUs (Nehalem, Westmere, Sandybridge, Atoms or
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newer). On older Intel CPUs the acpi_idle driver is still used (if the BIOS
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provides C\-state ACPI tables).
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The intel_idle driver knows the sleep state capabilities of the processor and
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ignores ACPI BIOS exported processor sleep states tables.
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.SH "REMARKS"
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.LP
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By default only values of core zero are displayed. How to display settings of
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other cores is described in the cpupower(1) manpage in the \-\-cpu option
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section.
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.SH REFERENCES
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http://www.acpi.info/spec.htm
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.SH "FILES"
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.nf
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\fI/sys/devices/system/cpu/cpu*/cpuidle/state*\fP
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\fI/sys/devices/system/cpu/cpuidle/*\fP
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.fi
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.SH "AUTHORS"
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.nf
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Thomas Renninger <trenn@suse.de>
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.fi
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.SH "SEE ALSO"
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.LP
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2024-09-09 08:57:42 +00:00
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cpupower(1), cpupower\-monitor(1), cpupower\-info(1), cpupower\-set(1),
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cpupower\-idle\-set(1)
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