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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 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.
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.
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.
This page is part of release 3.52 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/.
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Copyright (c) 2009 Intel Corporation, Author Andi Kleen Description based on comments in arch/x86/kernel/cpuid.c %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |