cpuid — x86 CPUID access device
CPUID provides an interface for querying information about the x86 CPU.
The lower 32 bits of the file position is used as the
the upper 32 bits of the file position as the incoming
%ecx, the latter
intended for "counting"
This driver uses
CPUNUM is the minor number, and on an SMP
box will direct the access to CPU
CPUNUM as listed in
This file is protected so that it can be read only by the
root, or members of the
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
through subdirectories in
/sys/devices/system/cpu. Direct CPUID
access through this device should only be used in exceptional
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.
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.
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Copyright (c) 2009 Intel Corporation, Author Andi Kleen
Description based on comments in arch/x86/kernel/cpuid.c
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