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.

COLOPHON

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