GETCPU
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
getcpu - determine CPU and NUMA node on which the calling thread is running
SYNOPSIS
#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.
DESCRIPTION
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is no longer current by the time the call returns.
RETURN VALUE
On success, 0 is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- EFAULT
-
Arguments point outside the calling process's address space.
VERSIONS
getcpu()
was added in kernel 2.6.19 for x86_64 and i386.
CONFORMING TO
getcpu()
is Linux-specific.
NOTES
Linux makes a best effort to make this call as fast as possible.
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the returned information would be out of date.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.
SEE ALSO
mbind(2),
sched_setaffinity(2),
set_mempolicy(2),
sched_getcpu(3),
cpuset(7),
vdso(7)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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