<div dir="ltr">1M is the default stack size. x86 and x86_64 have large stack size defaults, presumably because somebody at Intel decided that was better for some reason.<br><br>It would certainly improve the portability of the LLVM OpenMP runtime if the non-x86 default was 4M, at least on 64-bit systems.<br><br>From kmp.h:<br><br>#if KMP_ARCH_X86<br>#define KMP_DEFAULT_STKSIZE ((size_t)(2 * 1024 * 1024))<br>#elif KMP_ARCH_X86_64<br>#define KMP_DEFAULT_STKSIZE ((size_t)(4 * 1024 * 1024))<br>#define KMP_BACKUP_STKSIZE ((size_t)(2 * 1024 * 1024))<br>#else<br>#define KMP_DEFAULT_STKSIZE ((size_t)(1024 * 1024))<br>#endif<br><br>If I was going to change it, I would group all the 32-bit and all the 64-bit architectures to be the same, at least until somebody proves that one of them deserves specialization. I don't know what KMP_BACKUP_STKSIZE does but if that is x86_64-specific, then one can uncomment the relevant code below.<br><br>#if KMP_ARCH_X86 || KMP_ARCH_ARM ||
KMP_ARCH_MIPS<div>#define KMP_DEFAULT_STKSIZE ((size_t)(2 * 1024 * 1024))<br>#elif KMP_ARCH_X86_64 || KMP_ARCH_AARCH64 || KMP_ARCH_PPC64 || KMP_ARCH_MIPS64<br>#define KMP_DEFAULT_STKSIZE ((size_t)(4 * 1024 * 1024))</div><div>//#if KMP_ARCH_X86_64<br><div>#define KMP_BACKUP_STKSIZE ((size_t)(2 * 1024 * 1024))</div><div>//#endif<br>#else<br>#define KMP_DEFAULT_STKSIZE ((size_t)(4*1024 * 1024))<br>#endif<br><div><br></div><div>Jeff<br><div><br><div class="gmail_quote"><div dir="ltr">On Mon, Oct 8, 2018 at 8:21 AM Cownie, James H via Openmp-dev <<a href="mailto:openmp-dev@lists.llvm.org">openmp-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div lang="EN-GB" link="#0563C1" vlink="#954F72">
<div class="m_7956687119395904920WordSection1">
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">I cannot answer the question of why the PPC port chose a different stack size :-)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">But that doesn’t affect the solution, which, as you suggested, is to force the issue with
</span><span style="font-size:10.0pt;font-family:"Lucida Console";color:#1f497d">OMP_STACKSIZE</span><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<div>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">-- Jim<br>
<br>
Jim Cownie <<a href="mailto:james.h.cownie@intel.com" target="_blank">james.h.cownie@intel.com</a>><br>
CVCG/DPD/TCAR (Technical Computing, Analyzers, and Runtimes)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">Tel: +44 117 9071438</span><span style="color:#1f497d"><u></u><u></u></span></p>
</div>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<div>
<div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><a name="m_7956687119395904920______replyseparator"></a><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Simone Atzeni [mailto:<a href="mailto:satzeni@nvidia.com" target="_blank">satzeni@nvidia.com</a>]
<br>
<b>Sent:</b> Monday, October 8, 2018 4:16 PM<br>
<b>To:</b> Cownie, James H <<a href="mailto:james.h.cownie@intel.com" target="_blank">james.h.cownie@intel.com</a>><br>
<b>Cc:</b> <a href="mailto:openmp-dev@lists.llvm.org" target="_blank">openmp-dev@lists.llvm.org</a><br>
<b>Subject:</b> RE: Default value for OpenMP thread stacksize<u></u><u></u></span></p>
</div>
</div>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-US">It looks though the LLVM OpenMP runtime has two different stack size for x86 (4096kb) and power (1024kb), so I thought that this is not implementation related but maybe architecture dependent?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Anyway, makes sense to set the OMP_STACKSIZE.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Simone<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<div>
<div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Cownie, James H <<a href="mailto:james.h.cownie@intel.com" target="_blank">james.h.cownie@intel.com</a>>
<br>
<b>Sent:</b> Monday, October 8, 2018 5:05 PM<br>
<b>To:</b> Simone Atzeni <<a href="mailto:satzeni@nvidia.com" target="_blank">satzeni@nvidia.com</a>><br>
<b>Cc:</b> <a href="mailto:openmp-dev@lists.llvm.org" target="_blank">openmp-dev@lists.llvm.org</a><br>
<b>Subject:</b> RE: Default value for OpenMP thread stacksize<u></u><u></u></span></p>
</div>
</div>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">I do not know what the default OpenMP stack size is on PPC, but the rest of your logic seems sound, and setting
</span><span style="font-size:10.0pt;font-family:"Lucida Console";color:#1f497d">OMP_STACKSIZE</span><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d"> seems entirely reasonable.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">The standard says that the default stack size is “implementation defined”, so it is entirely reasonable that different implementations have different default
values.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<div>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">-- Jim<br>
<br>
Jim Cownie <<a href="mailto:james.h.cownie@intel.com" target="_blank">james.h.cownie@intel.com</a>><br>
CVCG/DPD/TCAR (Technical Computing, Analyzers, and Runtimes)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d">Tel: +44 117 9071438</span><span style="color:#1f497d"><u></u><u></u></span></p>
</div>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<div>
<div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Openmp-dev [<a href="mailto:openmp-dev-bounces@lists.llvm.org" target="_blank">mailto:openmp-dev-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Simone Atzeni via Openmp-dev<br>
<b>Sent:</b> Monday, October 8, 2018 3:58 PM<br>
<b>To:</b> <a href="mailto:openmp-dev@lists.llvm.org" target="_blank">openmp-dev@lists.llvm.org</a><br>
<b>Subject:</b> [Openmp-dev] Default value for OpenMP thread stacksize<u></u><u></u></span></p>
</div>
</div>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-US">HI all,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">What’s the default size for the stack of the OpenMP threads in x86 and and ppc64 in the OpenMP runtime?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">I have a Fortran program which allocates more than a 1MB on the stack for each thread. On x86 runs correctly, but on ppc64 it seg faults.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">I am seeing that each thread in x86 has a stacksize of 4096kb while on ppc64 is 1024kb.
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">If I increase the stacksize with OMP_STACKSIZE the program runs correctly also on Power, but it fails if I only set “ulimit -s unlimited”, which make sense since ulimit should only change the stacksize for the main thread
but not for the other threads.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Is this the expected behavior and the correct solution is to set OMP_STACKSIZE?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US">Simone<u></u><u></u></span></p>
<div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">Jeff Hammond<br><a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a><br><a href="http://jeffhammond.github.io/" target="_blank">http://jeffhammond.github.io/</a></div></div></div></div></div></div>