getcpu — determine CPU and NUMA node on which the calling thread is running
|struct getcpu_cache *tcache
|There is no glibc wrapper for this system call; see NOTES.|
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
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
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
node is no longer
current by the time the call returns.
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.
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information would be out of date.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.
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This man page is Copyright (C) 2006 Andi Kleen <akmuc.de>.
Permission is granted to distribute possibly modified copies
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and in case of nontrivial modification author and date
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2008, mtk, various edits