| NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
CPUID(4) Linux Programmer's Manual CPUID(4)
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 only be read 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 3.32 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)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface