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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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GETCPU(2) Linux Programmer's Manual GETCPU(2)
getcpu - determine CPU and NUMA node on which the calling thread is
running
#include <linux/getcpu.h>
int getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache);
Note: There is no glibc wrapper for this system call; see NOTES.
The getcpu() system call identifies the processor and node on which
the calling thread or process is currently running and writes them
into the integers pointed to by the cpu and node arguments. The
processor is a unique small integer identifying a CPU. The node is a
unique small identifier identifying a NUMA node. When either cpu or
node is NULL nothing is written to the respective pointer.
The third argument to this system call is nowadays unused, and should
be specified as NULL unless portability to Linux 2.6.23 or earlier is
required (see NOTES).
The information placed in cpu is guaranteed to be current only at the
time of the call: unless the CPU affinity has been fixed using
sched_setaffinity(2), the kernel might change the CPU at any time.
(Normally this does not happen because the scheduler tries to
minimize movements between CPUs to keep caches hot, but it is
possible.) The caller must allow for the possibility that the
information returned in cpu and node is no longer current by the time
the call returns.
On success, 0 is returned. On error, -1 is returned, and errno is
set appropriately.
EFAULT Arguments point outside the calling process's address space.
getcpu() was added in kernel 2.6.19 for x86-64 and i386.
getcpu() is Linux-specific.
Linux makes a best effort to make this call as fast as possible. (On
some architectures, this is done via an implementation in the
vdso(7).) The intention of getcpu() is to allow programs to make
optimizations with per-CPU data or for NUMA optimization.
Glibc does not provide a wrapper for this system call; call it using
syscall(2); or use sched_getcpu(3) instead.
The tcache argument is unused since Linux 2.6.24. In earlier
kernels, if this argument was non-NULL, then it specified a pointer
to a caller-allocated buffer in thread-local storage that was used to
provide a caching mechanism for getcpu(). Use of the cache could
speed getcpu() calls, at the cost that there was a very small chance
that the returned information would be out of date. The caching
mechanism was considered to cause problems when migrating threads
between CPUs, and so the argument is now ignored.
mbind(2), sched_setaffinity(2), set_mempolicy(2), sched_getcpu(3),
cpuset(7), vdso(7)
This 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/.
Linux 2017-09-15 GETCPU(2)
Pages that refer to this page: get_mempolicy(2), mbind(2), sched_setaffinity(2), set_mempolicy(2), syscalls(2), sched_getcpu(3), cpuset(7)
Copyright and license for this manual page
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