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<title>GNU libgomp: OMP_PLACES</title>
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<a name="OMP_005fPLACES"></a>
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<p>
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Next: <a href="OMP_005fSTACKSIZE.html#OMP_005fSTACKSIZE" accesskey="n" rel="next">OMP_STACKSIZE</a>, Previous: <a href="OMP_005fPROC_005fBIND.html#OMP_005fPROC_005fBIND" accesskey="p" rel="prev">OMP_PROC_BIND</a>, Up: <a href="Environment-Variables.html#Environment-Variables" accesskey="u" rel="up">Environment Variables</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Library-Index.html#Library-Index" title="Index" rel="index">Index</a>]</p>
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<a name="OMP_005fPLACES-_002d_002d-Specifies-on-which-CPUs-the-theads-should-be-placed"></a>
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<h3 class="section">3.10 <code>OMP_PLACES</code> – Specifies on which CPUs the theads should be placed</h3>
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<a name="index-Environment-Variable-9"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p>The thread placement can be either specified using an abstract name or by an
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explicit list of the places. The abstract names <code>threads</code>, <code>cores</code>
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and <code>sockets</code> can be optionally followed by a positive number in
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parentheses, which denotes the how many places shall be created. With
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<code>threads</code> each place corresponds to a single hardware thread; <code>cores</code>
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to a single core with the corresponding number of hardware threads; and with
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<code>sockets</code> the place corresponds to a single socket. The resulting
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placement can be shown by setting the <code>OMP_DISPLAY_ENV</code> environment
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variable.
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</p>
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<p>Alternatively, the placement can be specified explicitly as comma-separated
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list of places. A place is specified by set of nonnegative numbers in curly
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braces, denoting the denoting the hardware threads. The hardware threads
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belonging to a place can either be specified as comma-separated list of
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nonnegative thread numbers or using an interval. Multiple places can also be
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either specified by a comma-separated list of places or by an interval. To
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specify an interval, a colon followed by the count is placed after after
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the hardware thread number or the place. Optionally, the length can be
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followed by a colon and the stride number – otherwise a unit stride is
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assumed. For instance, the following specifies the same places list:
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<code>"{0,1,2}, {3,4,6}, {7,8,9}, {10,11,12}"</code>;
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<code>"{0:3}, {3:3}, {7:3}, {10:3}"</code>; and <code>"{0:2}:4:3"</code>.
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</p>
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<p>If <code>OMP_PLACES</code> and <code>GOMP_CPU_AFFINITY</code> are unset and
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<code>OMP_PROC_BIND</code> is either unset or <code>false</code>, threads may be moved
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between CPUs following no placement policy.
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</p>
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</dd>
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<dt><em>See also</em>:</dt>
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<dd><p><a href="OMP_005fPROC_005fBIND.html#OMP_005fPROC_005fBIND">OMP_PROC_BIND</a>, <a href="GOMP_005fCPU_005fAFFINITY.html#GOMP_005fCPU_005fAFFINITY">GOMP_CPU_AFFINITY</a>, <a href="omp_005fget_005fproc_005fbind.html#omp_005fget_005fproc_005fbind">omp_get_proc_bind</a>,
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<a href="OMP_005fDISPLAY_005fENV.html#OMP_005fDISPLAY_005fENV">OMP_DISPLAY_ENV</a>
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</p>
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</dd>
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<dt><em>Reference</em>:</dt>
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<dd><p><a href="http://www.openmp.org/">OpenMP specification v4.5</a>, Section 4.5
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</p></dd>
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