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Linux/Documentation/cputopology.txt

  1 
  2 Export CPU topology info via sysfs. Items (attributes) are similar
  3 to /proc/cpuinfo output of some architectures:
  4 
  5 1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
  6 
  7         physical package id of cpuX. Typically corresponds to a physical
  8         socket number, but the actual value is architecture and platform
  9         dependent.
 10 
 11 2) /sys/devices/system/cpu/cpuX/topology/core_id:
 12 
 13         the CPU core ID of cpuX. Typically it is the hardware platform's
 14         identifier (rather than the kernel's).  The actual value is
 15         architecture and platform dependent.
 16 
 17 3) /sys/devices/system/cpu/cpuX/topology/book_id:
 18 
 19         the book ID of cpuX. Typically it is the hardware platform's
 20         identifier (rather than the kernel's).  The actual value is
 21         architecture and platform dependent.
 22 
 23 4) /sys/devices/system/cpu/cpuX/topology/drawer_id:
 24 
 25         the drawer ID of cpuX. Typically it is the hardware platform's
 26         identifier (rather than the kernel's).  The actual value is
 27         architecture and platform dependent.
 28 
 29 5) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
 30 
 31         internal kernel map of cpuX's hardware threads within the same
 32         core as cpuX.
 33 
 34 6) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
 35 
 36         human-readable list of cpuX's hardware threads within the same
 37         core as cpuX.
 38 
 39 7) /sys/devices/system/cpu/cpuX/topology/core_siblings:
 40 
 41         internal kernel map of cpuX's hardware threads within the same
 42         physical_package_id.
 43 
 44 8) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
 45 
 46         human-readable list of cpuX's hardware threads within the same
 47         physical_package_id.
 48 
 49 9) /sys/devices/system/cpu/cpuX/topology/book_siblings:
 50 
 51         internal kernel map of cpuX's hardware threads within the same
 52         book_id.
 53 
 54 10) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
 55 
 56         human-readable list of cpuX's hardware threads within the same
 57         book_id.
 58 
 59 11) /sys/devices/system/cpu/cpuX/topology/drawer_siblings:
 60 
 61         internal kernel map of cpuX's hardware threads within the same
 62         drawer_id.
 63 
 64 12) /sys/devices/system/cpu/cpuX/topology/drawer_siblings_list:
 65 
 66         human-readable list of cpuX's hardware threads within the same
 67         drawer_id.
 68 
 69 To implement it in an architecture-neutral way, a new source file,
 70 drivers/base/topology.c, is to export the 6 to 12 attributes. The book
 71 and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
 72 and CONFIG_SCHED_DRAWER are selected.
 73 
 74 CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
 75 they reflect the cpu and cache hierarchy.
 76 
 77 For an architecture to support this feature, it must define some of
 78 these macros in include/asm-XXX/topology.h:
 79 #define topology_physical_package_id(cpu)
 80 #define topology_core_id(cpu)
 81 #define topology_book_id(cpu)
 82 #define topology_drawer_id(cpu)
 83 #define topology_sibling_cpumask(cpu)
 84 #define topology_core_cpumask(cpu)
 85 #define topology_book_cpumask(cpu)
 86 #define topology_drawer_cpumask(cpu)
 87 
 88 The type of **_id macros is int.
 89 The type of **_cpumask macros is (const) struct cpumask *. The latter
 90 correspond with appropriate **_siblings sysfs attributes (except for
 91 topology_sibling_cpumask() which corresponds with thread_siblings).
 92 
 93 To be consistent on all architectures, include/linux/topology.h
 94 provides default definitions for any of the above macros that are
 95 not defined by include/asm-XXX/topology.h:
 96 1) physical_package_id: -1
 97 2) core_id: 0
 98 3) sibling_cpumask: just the given CPU
 99 4) core_cpumask: just the given CPU
100 
101 For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
102 default definitions for topology_book_id() and topology_book_cpumask().
103 For architectures that don't support drawes (CONFIG_SCHED_DRAWER) there are
104 no default definitions for topology_drawer_id() and topology_drawer_cpumask().
105 
106 Additionally, CPU topology information is provided under
107 /sys/devices/system/cpu and includes these files.  The internal
108 source for the output is in brackets ("[]").
109 
110     kernel_max: the maximum CPU index allowed by the kernel configuration.
111                 [NR_CPUS-1]
112 
113     offline:    CPUs that are not online because they have been
114                 HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
115                 of CPUs allowed by the kernel configuration (kernel_max
116                 above). [~cpu_online_mask + cpus >= NR_CPUS]
117 
118     online:     CPUs that are online and being scheduled [cpu_online_mask]
119 
120     possible:   CPUs that have been allocated resources and can be
121                 brought online if they are present. [cpu_possible_mask]
122 
123     present:    CPUs that have been identified as being present in the
124                 system. [cpu_present_mask]
125 
126 The format for the above output is compatible with cpulist_parse()
127 [see <linux/cpumask.h>].  Some examples follow.
128 
129 In this example, there are 64 CPUs in the system but cpus 32-63 exceed
130 the kernel max which is limited to 0..31 by the NR_CPUS config option
131 being 32.  Note also that CPUs 2 and 4-31 are not online but could be
132 brought online as they are both present and possible.
133 
134      kernel_max: 31
135         offline: 2,4-31,32-63
136          online: 0-1,3
137        possible: 0-31
138         present: 0-31
139 
140 In this example, the NR_CPUS config option is 128, but the kernel was
141 started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
142 was manually taken offline (and is the only CPU that can be brought
143 online.)
144 
145      kernel_max: 127
146         offline: 2,4-127,128-143
147          online: 0-1,3
148        possible: 0-127
149         present: 0-3
150 
151 See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
152 as well as more information on the various cpumasks.

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