1What:		/sys/devices/system/cpu/
2Date:		pre-git history
3Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
4Description:
5		A collection of both global and individual CPU attributes
6
7		Individual CPU attributes are contained in subdirectories
8		named by the kernel's logical CPU number, e.g.:
9
10		/sys/devices/system/cpu/cpu#/
11
12What:		/sys/devices/system/cpu/kernel_max
13		/sys/devices/system/cpu/offline
14		/sys/devices/system/cpu/online
15		/sys/devices/system/cpu/possible
16		/sys/devices/system/cpu/present
17Date:		December 2008
18Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
19Description:	CPU topology files that describe kernel limits related to
20		hotplug. Briefly:
21
22		kernel_max: the maximum cpu index allowed by the kernel
23		configuration.
24
25		offline: cpus that are not online because they have been
26		HOTPLUGGED off or exceed the limit of cpus allowed by the
27		kernel configuration (kernel_max above).
28
29		online: cpus that are online and being scheduled.
30
31		possible: cpus that have been allocated resources and can be
32		brought online if they are present.
33
34		present: cpus that have been identified as being present in
35		the system.
36
37		See Documentation/cputopology.txt for more information.
38
39
40What:		/sys/devices/system/cpu/probe
41		/sys/devices/system/cpu/release
42Date:		November 2009
43Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
44Description:	Dynamic addition and removal of CPU's.  This is not hotplug
45		removal, this is meant complete removal/addition of the CPU
46		from the system.
47
48		probe: writes to this file will dynamically add a CPU to the
49		system.  Information written to the file to add CPU's is
50		architecture specific.
51
52		release: writes to this file dynamically remove a CPU from
53		the system.  Information writtento the file to remove CPU's
54		is architecture specific.
55
56What:		/sys/devices/system/cpu/cpu#/node
57Date:		October 2009
58Contact:	Linux memory management mailing list <linux-mm@kvack.org>
59Description:	Discover NUMA node a CPU belongs to
60
61		When CONFIG_NUMA is enabled, a symbolic link that points
62		to the corresponding NUMA node directory.
63
64		For example, the following symlink is created for cpu42
65		in NUMA node 2:
66
67		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
68
69
70What:		/sys/devices/system/cpu/cpu#/topology/core_id
71		/sys/devices/system/cpu/cpu#/topology/core_siblings
72		/sys/devices/system/cpu/cpu#/topology/core_siblings_list
73		/sys/devices/system/cpu/cpu#/topology/physical_package_id
74		/sys/devices/system/cpu/cpu#/topology/thread_siblings
75		/sys/devices/system/cpu/cpu#/topology/thread_siblings_list
76Date:		December 2008
77Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
78Description:	CPU topology files that describe a logical CPU's relationship
79		to other cores and threads in the same physical package.
80
81		One cpu# directory is created per logical CPU in the system,
82		e.g. /sys/devices/system/cpu/cpu42/.
83
84		Briefly, the files above are:
85
86		core_id: the CPU core ID of cpu#. Typically it is the
87		hardware platform's identifier (rather than the kernel's).
88		The actual value is architecture and platform dependent.
89
90		core_siblings: internal kernel map of cpu#'s hardware threads
91		within the same physical_package_id.
92
93		core_siblings_list: human-readable list of the logical CPU
94		numbers within the same physical_package_id as cpu#.
95
96		physical_package_id: physical package id of cpu#. Typically
97		corresponds to a physical socket number, but the actual value
98		is architecture and platform dependent.
99
100		thread_siblings: internel kernel map of cpu#'s hardware
101		threads within the same core as cpu#
102
103		thread_siblings_list: human-readable list of cpu#'s hardware
104		threads within the same core as cpu#
105
106		See Documentation/cputopology.txt for more information.
107
108
109What:		/sys/devices/system/cpu/cpuidle/current_driver
110		/sys/devices/system/cpu/cpuidle/current_governer_ro
111Date:		September 2007
112Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
113Description:	Discover cpuidle policy and mechanism
114
115		Various CPUs today support multiple idle levels that are
116		differentiated by varying exit latencies and power
117		consumption during idle.
118
119		Idle policy (governor) is differentiated from idle mechanism
120		(driver)
121
122		current_driver: displays current idle mechanism
123
124		current_governor_ro: displays current idle policy
125
126		See files in Documentation/cpuidle/ for more information.
127
128
129What:		/sys/devices/system/cpu/cpu#/cpufreq/*
130Date:		pre-git history
131Contact:	cpufreq@vger.kernel.org
132Description:	Discover and change clock speed of CPUs
133
134		Clock scaling allows you to change the clock speed of the
135		CPUs on the fly. This is a nice method to save battery
136		power, because the lower the clock speed, the less power
137		the CPU consumes.
138
139		There are many knobs to tweak in this directory.
140
141		See files in Documentation/cpu-freq/ for more information.
142
143		In particular, read Documentation/cpu-freq/user-guide.txt
144		to learn how to control the knobs.
145
146
147What:		/sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
148Date:		June 2013
149Contact:	cpufreq@vger.kernel.org
150Description:	Discover CPUs in the same CPU frequency coordination domain
151
152		freqdomain_cpus is the list of CPUs (online+offline) that share
153		the same clock/freq domain (possibly at the hardware level).
154		That information may be hidden from the cpufreq core and the
155		value of related_cpus may be different from freqdomain_cpus. This
156		attribute is useful for user space DVFS controllers to get better
157		power/performance results for platforms using acpi-cpufreq.
158
159		This file is only present if the acpi-cpufreq driver is in use.
160
161
162What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
163Date:		August 2008
164KernelVersion:	2.6.27
165Contact:	discuss@x86-64.org
166Description:	Disable L3 cache indices
167
168		These files exist in every CPU's cache/index3 directory. Each
169		cache_disable_{0,1} file corresponds to one disable slot which
170		can be used to disable a cache index. Reading from these files
171		on a processor with this functionality will return the currently
172		disabled index for that node. There is one L3 structure per
173		node, or per internal node on MCM machines. Writing a valid
174		index to one of these files will cause the specificed cache
175		index to be disabled.
176
177		All AMD processors with L3 caches provide this functionality.
178		For details, see BKDGs at
179		http://developer.amd.com/documentation/guides/Pages/default.aspx
180
181
182What:		/sys/devices/system/cpu/cpufreq/boost
183Date:		August 2012
184Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
185Description:	Processor frequency boosting control
186
187		This switch controls the boost setting for the whole system.
188		Boosting allows the CPU and the firmware to run at a frequency
189		beyound it's nominal limit.
190		More details can be found in Documentation/cpu-freq/boost.txt
191
192
193What:		/sys/devices/system/cpu/cpu#/crash_notes
194		/sys/devices/system/cpu/cpu#/crash_notes_size
195Date:		April 2013
196Contact:	kexec@lists.infradead.org
197Description:	address and size of the percpu note.
198
199		crash_notes: the physical address of the memory that holds the
200		note of cpu#.
201
202		crash_notes_size: size of the note of cpu#.
203