CPUIDSection: Linux Programmer's Manual (4)
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NAMEcpuid - x86 CPUID access device
DESCRIPTIONCPUID provides an interface for querying information about the x86 CPU.
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.
NOTESThe 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.
SEE ALSOIntel Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A: Instruction Set Reference, A-M, 3-180 CPUID reference.
COLOPHONThis page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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