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


     cpuid - x86 CPUID access device


     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.


     The  CPUID  instruction  can  be  directly  executed by a program using
     inline 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/devices/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
     Very old x86 CPUs don't support CPUID.


     Intel Corporation, Intel 64 and  IA-32  Architectures  Software  Devel-
     oper's  Manual  Volume  2A: Instruction Set Reference, A-M, 3-180 CPUID
     Intel  Corporation,  Intel  Processor  Identification  and  the   CPUID
     Instruction, Application note 485.


     This  page  is  part of release 4.16 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

Linux 2009-03-31 CPUID(4)

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