diff options
| author | Alejandro Colomar <alx@kernel.org> | 2024-04-26 15:06:49 +0200 |
|---|---|---|
| committer | Alejandro Colomar <alx@kernel.org> | 2024-05-02 01:24:19 +0200 |
| commit | dcde2f70372b49ec43efc5db864c9ff585d0a2dd (patch) | |
| tree | 78b9b7425130e4a5858e4c01a524d802423879ed /man/man2/getcpu.2 | |
| parent | 12aca537ce78a41bbcdaf485209691e10f8002d7 (diff) | |
| download | man-pages-dcde2f70372b49ec43efc5db864c9ff585d0a2dd.tar.gz | |
man/, share/mk/: Move man*/ to man/
This is a scripted change:
$ mkdir man/;
$ mv man* man/;
$ ln -st . man/man*;
$ find share/mk/ -type f \
| xargs grep -l '^MANDIR *:=' \
| xargs sed -i '/^MANDIR *:=/s,$,/man,';
$ find share/mk/dist/ -type f \
| xargs grep -l man \
| xargs sed -i 's,man%,man/%,g';
Link: <https://lore.kernel.org/linux-man/YxcV4h+Xn7cd6+q2@pevik/T/>
Cc: Petr Vorel <pvorel@suse.cz>
Cc: Jakub Wilk <jwilk@jwilk.net>
Cc: Stefan Puiu <stefan.puiu@gmail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Diffstat (limited to 'man/man2/getcpu.2')
| -rw-r--r-- | man/man2/getcpu.2 | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/man/man2/getcpu.2 b/man/man2/getcpu.2 new file mode 100644 index 0000000000..72c500f97d --- /dev/null +++ b/man/man2/getcpu.2 @@ -0,0 +1,147 @@ +.\" SPDX-License-Identifier: Linux-man-pages-1-para +.\" +.\" This man page is Copyright (C) 2006 Andi Kleen <ak@muc.de>. +.\" +.\" 2008, mtk, various edits +.\" +.TH getcpu 2 (date) "Linux man-pages (unreleased)" +.SH NAME +getcpu \- determine CPU and NUMA node on which the calling thread is running +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" +.B #include <sched.h> +.P +.BI "int getcpu(unsigned int *_Nullable " cpu ", \ +unsigned int *_Nullable " node ); +.fi +.SH DESCRIPTION +The +.BR 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 +.I cpu +and +.I 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 +.I cpu +or +.I node +is NULL nothing is written to the respective pointer. +.P +The information placed in +.I cpu +is guaranteed to be current only at the time of the call: +unless the CPU affinity has been fixed using +.BR 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 +.I cpu +and +.I node +is no longer current by the time the call returns. +.SH RETURN VALUE +On success, 0 is returned. +On error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EFAULT +Arguments point outside the calling process's address space. +.SH STANDARDS +Linux. +.SH HISTORY +Linux 2.6.19 (x86-64 and i386), +glibc 2.29. +.\" +.SS C library/kernel differences +The kernel system call has a third argument: +.P +.in +4n +.nf +.BI "int getcpu(unsigned int *" cpu ", unsigned int *" node , +.BI " struct getcpu_cache *" tcache ); +.fi +.in +.P +The +.I tcache +argument is unused since Linux 2.6.24, +and (when invoking the system call directly) +should be specified as NULL, +unless portability to Linux 2.6.23 or earlier is required. +.P +.\" commit 4307d1e5ada595c87f9a4d16db16ba5edb70dcb1 +.\" Author: Ingo Molnar <mingo@elte.hu> +.\" Date: Wed Nov 7 18:37:48 2007 +0100 +.\" x86: ignore the sys_getcpu() tcache parameter +In Linux 2.6.23 and earlier, if the +.I tcache +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 +.BR getcpu (). +Use of the cache could speed +.BR 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. +.\" +.\" ===== Before Linux 2.6.24: ===== +.\" .I tcache +.\" is a pointer to a +.\" .IR "struct getcpu_cache" +.\" that is used as a cache by +.\" .BR getcpu (). +.\" The caller should put the cache into a thread-local variable +.\" if the process is multithreaded, +.\" because the cache cannot be shared between different threads. +.\" .I tcache +.\" can be NULL. +.\" If it is not NULL +.\" .BR getcpu () +.\" will use it to speed up operation. +.\" The information inside the cache is private to the system call +.\" and should not be accessed by the user program. +.\" The information placed in the cache can change between Linux releases. +.\" +.\" When no cache is specified +.\" .BR getcpu () +.\" will be slower, +.\" but always retrieve the current CPU and node information. +.\" With a cache +.\" .BR getcpu () +.\" is faster. +.\" However, the cached information is updated only once per jiffy (see +.\" .BR time (7)). +.\" This means that the information could theoretically be out of date, +.\" although in practice the scheduler's attempt to maintain +.\" soft CPU affinity means that the information is unlikely to change +.\" over the course of the caching interval. +.SH NOTES +Linux makes a best effort to make this call as fast as possible. +(On some architectures, this is done via an implementation in the +.BR vdso (7).) +The intention of +.BR getcpu () +is to allow programs to make optimizations with per-CPU data +or for NUMA optimization. +.SH SEE ALSO +.BR mbind (2), +.BR sched_setaffinity (2), +.BR set_mempolicy (2), +.BR sched_getcpu (3), +.BR cpuset (7), +.BR vdso (7) |