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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);
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the information returned in cpu and node is no longer current by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. Library
support was added in glibc 2.29 (Earlier glibc versions did not
provide a wrapper for this system call, necessitating the use of
syscall(2).)
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.
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very small chance that the returned information would be out of
date.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 5.10 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 2019-03-06 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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