| .TH "CPUPOWER-IDLE-INFO" "1" "0.1" "" "cpupower Manual" |
| .SH "NAME" |
| .LP |
| cpupower\-idle\-info \- Utility to retrieve cpu idle kernel information |
| .SH "SYNTAX" |
| .LP |
| cpupower [ \-c cpulist ] idle\-info [\fIoptions\fP] |
| .SH "DESCRIPTION" |
| .LP |
| A tool which prints out per cpu idle information helpful to developers and interested users. |
| .SH "OPTIONS" |
| .LP |
| .TP |
| \fB\-f\fR \fB\-\-silent\fR |
| Only print a summary of all available C-states in the system. |
| .TP |
| \fB\-e\fR \fB\-\-proc\fR |
| 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. |
| |
| .SH 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. |
| |
| .SH IDLE\-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS |
| .SS "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. |
| |
| .SH "REMARKS" |
| .LP |
| 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. |
| .SH REFERENCES |
| http://www.acpi.info/spec.htm |
| .SH "FILES" |
| .nf |
| \fI/sys/devices/system/cpu/cpu*/cpuidle/state*\fP |
| \fI/sys/devices/system/cpu/cpuidle/*\fP |
| .fi |
| .SH "AUTHORS" |
| .nf |
| Thomas Renninger <trenn@suse.de> |
| .fi |
| .SH "SEE ALSO" |
| .LP |
| cpupower(1), cpupower\-monitor(1), cpupower\-info(1), cpupower\-set(1), |
| cpupower\-idle\-set(1) |
