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 is 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 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 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 registers.

       Very old x86 CPUs don't support CPUID.

SEE ALSO
       cpuid(1)

       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.

Linux                                                                          2019-08-02                                                                       CPUID(4)