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 number, 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 only be read by the user root, or members of the group root.

NOTES
       The CPUID instruction can be directly executed by a program using inline assembler.  However this  device  allows  conve-
       nient 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 subdirecto-
       ries 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  explic-
       itly 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
       Intel  Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A: Instruction Set Reference, A-
       M, 3-180 CPUID reference.

       Intel Corporation, Intel Processor Identification and the CPUID Instruction, Application note 485.

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2009-03-31                                                   CPUID(4)