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


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


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


   -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.


   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.


   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

   "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.


   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.






   Thomas Renninger <trenn@suse.de>


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

                                  0.1                CPUPOWER-IDLE-INFO(1)

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