1.TH "CPUPOWER-IDLE-INFO" "1" "0.1" "" "cpupower Manual" 2.SH "NAME" 3.LP 4cpupower idle\-info \- Utility to retrieve cpu idle kernel information 5.SH "SYNTAX" 6.LP 7cpupower [ \-c cpulist ] idle\-info [\fIoptions\fP] 8.SH "DESCRIPTION" 9.LP 10A tool which prints out per cpu idle information helpful to developers and interested users. 11.SH "OPTIONS" 12.LP 13.TP 14\fB\-f\fR \fB\-\-silent\fR 15Only print a summary of all available C-states in the system. 16.TP 17\fB\-e\fR \fB\-\-proc\fR 18deprecated. 19Prints out idle information in old /proc/acpi/processor/*/power format. This 20interface has been removed from the kernel for quite some time, do not let 21further code depend on this option, best do not use it. 22 23.SH IDLE\-INFO DESCRIPTIONS 24CPU sleep state statistics and descriptions are retrieved from sysfs files, 25exported by the cpuidle kernel subsystem. The kernel only updates these 26statistics when it enters or leaves an idle state, therefore on a very idle or 27a very busy system, these statistics may not be accurate. They still provide a 28good overview about the usage and availability of processor sleep states on 29the platform. 30 31Be aware that the sleep states as exported by the hardware or BIOS and used by 32the Linux kernel may not exactly reflect the capabilities of the 33processor. This often is the case on the X86 architecture when the acpi_idle 34driver is used. It is also possible that the hardware overrules the kernel 35requests, due to internal activity monitors or other reasons. 36On recent X86 platforms it is often possible to read out hardware registers 37which monitor the duration of sleep states the processor resided in. The 38cpupower monitor tool (cpupower\-monitor(1)) can be used to show real sleep 39state residencies. Please refer to the architecture specific description 40section below. 41 42.SH IDLE\-INFO ARCHITECTURE SPECIFIC DESCRIPTIONS 43.SS "X86" 44POLL idle state 45 46If cpuidle is active, X86 platforms have one special idle state. 47The POLL idle state is not a real idle state, it does not save any 48power. Instead, a busy\-loop is executed doing nothing for a short period of 49time. This state is used if the kernel knows that work has to be processed 50very soon and entering any real hardware idle state may result in a slight 51performance penalty. 52 53There exist two different cpuidle drivers on the X86 architecture platform: 54 55"acpi_idle" cpuidle driver 56 57The acpi_idle cpuidle driver retrieves available sleep states (C\-states) from 58the ACPI BIOS tables (from the _CST ACPI function on recent platforms or from 59the FADT BIOS table on older ones). 60The C1 state is not retrieved from ACPI tables. If the C1 state is entered, 61the kernel will call the hlt instruction (or mwait on Intel). 62 63"intel_idle" cpuidle driver 64 65In kernel 2.6.36 the intel_idle driver was introduced. 66It only serves recent Intel CPUs (Nehalem, Westmere, Sandybridge, Atoms or 67newer). On older Intel CPUs the acpi_idle driver is still used (if the BIOS 68provides C\-state ACPI tables). 69The intel_idle driver knows the sleep state capabilities of the processor and 70ignores ACPI BIOS exported processor sleep states tables. 71 72.SH "REMARKS" 73.LP 74By default only values of core zero are displayed. How to display settings of 75other cores is described in the cpupower(1) manpage in the \-\-cpu option 76section. 77.SH REFERENCES 78http://www.acpi.info/spec.htm 79.SH "FILES" 80.nf 81\fI/sys/devices/system/cpu/cpu*/cpuidle/state*\fP 82\fI/sys/devices/system/cpu/cpuidle/*\fP 83.fi 84.SH "AUTHORS" 85.nf 86Thomas Renninger <trenn@suse.de> 87.fi 88.SH "SEE ALSO" 89.LP 90cpupower(1), cpupower\-monitor(1), cpupower\-info(1), cpupower\-set(1) 91