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)