xenial (1) cpupower-idle-info.1.gz

NAME

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

SYNTAX

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

DESCRIPTION

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

OPTIONS

       -f --silent
              Only print a summary of all available C-states in the system.

       -e --proc
              deprecated.   Prints  out  idle  information  in  old  /proc/acpi/processor/*/power  format.  This
              interface has been removed from the kernel for quite some time, do not let further code depend  on
              this option, best do not use it.

IDLE-INFO DESCRIPTIONS

       CPU  sleep  state  statistics  and  descriptions  are retrieved from sysfs files, exported by the cpuidle
       kernel subsystem. The kernel only updates these statistics when  it  enters  or  leaves  an  idle  state,
       therefore  on a very idle or a very busy system, these statistics may not be accurate. They still provide
       a good overview about the usage and availability of processor sleep states on the platform.

       Be aware that the sleep states as exported by the hardware or BIOS and used by the Linux kernel  may  not
       exactly  reflect  the  capabilities of the processor. This often is the case on the X86 architecture when
       the acpi_idle driver is used. It is also possible that the hardware overrules the kernel requests, due to
       internal  activity  monitors  or other reasons.  On recent X86 platforms it is often possible to read out
       hardware registers which monitor the duration of sleep states the  processor  resided  in.  The  cpupower
       monitor  tool (cpupower-monitor(1)) can be used to show real sleep state residencies. Please refer to the
       architecture specific description section below.

IDLE-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS

   X86
       POLL idle state

       If cpuidle is active, X86 platforms have one special idle state.  The POLL idle state is not a real  idle
       state,  it  does not save any power. Instead, a busy-loop is executed doing nothing for a short period of
       time. This state is used if the kernel knows that work has to be processed very  soon  and  entering  any
       real hardware idle state may result in a slight performance penalty.

       There exist two different cpuidle drivers on the X86 architecture platform:

       "acpi_idle" cpuidle driver

       The  acpi_idle cpuidle driver retrieves available sleep states (C-states) from the ACPI BIOS tables (from
       the _CST ACPI function on recent platforms or from the FADT BIOS table on older ones).  The C1  state  is
       not  retrieved from ACPI tables. If the C1 state is entered, the kernel will call the hlt instruction (or
       mwait on Intel).

       "intel_idle" cpuidle driver

       In kernel 2.6.36 the intel_idle driver was introduced.   It  only  serves  recent  Intel  CPUs  (Nehalem,
       Westmere,  Sandybridge,  Atoms  or newer). On older Intel CPUs the acpi_idle driver is still used (if the
       BIOS provides C-state ACPI tables).  The intel_idle driver knows the  sleep  state  capabilities  of  the
       processor and ignores ACPI BIOS exported processor sleep states tables.

REMARKS

       By default only values of core zero are displayed. How to display settings of other cores is described in
       the cpupower(1) manpage in the --cpu option section.

REFERENCES

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

FILES

       /sys/devices/system/cpu/cpu*/cpuidle/state*
       /sys/devices/system/cpu/cpuidle/*

AUTHORS

       Thomas Renninger <trenn@suse.de>

SEE ALSO

       cpupower(1), cpupower-monitor(1), cpupower-info(1), cpupower-set(1), cpupower-idle-set(1)

                                                       0.1                                 CPUPOWER-IDLE-INFO(1)