1CPUID(4)                   Linux Programmer's Manual                  CPUID(4)
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NAME

6       cpuid - x86 CPUID access device
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DESCRIPTION

9       CPUID provides an interface for querying information about the x86 CPU.
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11       This  device  is  accessed  by  lseek(2) or pread(2) to the appropriate
12       CPUID level and reading in chunks of 16  bytes.   A  larger  read  size
13       means multiple reads of consecutive levels.
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15       The  lower  32  bits of the file position is used as the incoming %eax,
16       and the upper 32 bits of the file position as the  incoming  %ecx,  the
17       latter is intended for "counting" eax levels like eax=4.
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19       This  driver uses /dev/cpu/CPUNUM/cpuid, where CPUNUM is the minor num‐
20       ber, and on an SMP box will direct the access to CPU CPUNUM  as  listed
21       in /proc/cpuinfo.
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23       This file is protected so that it can be read only by the user root, or
24       members of the group root.
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NOTES

27       The CPUID instruction can be directly executed by a program  using  in‐
28       line  assembler.   However  this device allows convenient access to all
29       CPUs without changing process affinity.
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31       Most of the information in cpuid is reported by the  kernel  in  cooked
32       form  either  in  /proc/cpuinfo  or  through subdirectories in /sys/de‐
33       vices/system/cpu.  Direct CPUID access through this device should  only
34       be used in exceptional cases.
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36       The cpuid driver is not auto-loaded.  On modular kernels you might need
37       to use the following command to load it explicitly before use:
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39           $ modprobe cpuid
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41       There is no support for CPUID functions that require  additional  input
42       registers.
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44       Very old x86 CPUs don't support CPUID.
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SEE ALSO

47       cpuid(1)
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49       Intel  Corporation,  Intel  64  and IA-32 Architectures Software Devel‐
50       oper's Manual Volume 2A: Instruction Set Reference,  A-M,  3-180  CPUID
51       reference.
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53       Intel  Corporation,  Intel  Processor  Identification and the CPUID In‐
54       struction, Application note 485.
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COLOPHON

57       This page is part of release 5.13 of the Linux  man-pages  project.   A
58       description  of  the project, information about reporting bugs, and the
59       latest    version    of    this    page,    can     be     found     at
60       https://www.kernel.org/doc/man-pages/.
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64Linux                             2019-08-02                          CPUID(4)
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