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