cpuid

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

NAME
       cpuid - x86 CPUID access device

DESCRIPTION
       CPUID provides an interface for querying information about the x86 CPU.

       This  device  is  accessed  by  lseek(2) or pread(2) to the appropriate
       CPUID level and reading in chunks of 16  bytes.   A  larger  read  size
       means multiple reads of consecutive levels.

       The  lower  32  bits of the file position is used as the incoming %eax,
       and the upper 32 bits of the file position as the  incoming  %ecx,  the
       latter intended for "counting" eax levels like eax=4.

       This  driver uses /dev/cpu/CPUNUM/cpuid, where CPUNUM is the minor num-
       ber, and on an SMP box will direct the access to CPU CPUNUM  as  listed
       in /proc/cpuinfo.

       This file is protected so that it can be read only by the user root, or
       members of the group root.

NOTES
       The CPUID instruction can be directly executed by a program  using  in-
       line  assembler.   However  this device allows convenient access to all
       CPUs without changing process affinity.

       Most of the information in cpuid is reported by the  kernel  in  cooked
       form  either  in  /proc/cpuinfo  or  through subdirectories in /sys/de-
       vices/system/cpu.  Direct CPUID access through this device should  only
       be used in exceptional cases.

       The cpuid driver is not auto-loaded.  On modular kernels you might need
       to use the following command to load it explicitly before use:

           $ modprobe cpuid

       There is no support for CPUID functions that require  additional  input
       registers.

       Very old x86 CPUs don't support CPUID.

SEE ALSO
       cpuid(1)

       Intel  Corporation,  Intel  64  and IA-32 Architectures Software Devel-
       oper's Manual Volume 2A: Instruction Set Reference,  A-M,  3-180  CPUID
       reference.

       Intel  Corporation,  Intel  Processor  Identification and the CPUID In-
       struction, Application note 485.

COLOPHON
       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2019-08-02                          CPUID(4)