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<p>Hello all,</p>
<p>I am trying to run on the new skylake processors on Stampede2 and
while the run speeds we are obtaining are very good, we are
concerned that we aren't optimizing properly when it comes to
OpenMP. For instance, we see the best speeds when we use 8 MPI
processors per node (with 6 threads each for a total of 48 total
threads/node). Based on the architecture, we were expecting to
see the best speeds with 2 MPI/node. Here is what I have tried:</p>
<ol>
<li>Using the simfactory files for stampede2-skx (config file, run
and submit scripts, and modules loaded) I compiled a version of
ET_2017_06 using LazEv (RIT's evolution thorn) and McLachlan and
submitted a series of runs that change both the number of nodes
used, and how I distribute the 48 threads/node between MPI
processes.<br>
</li>
<li>I use a standard low resolution grid, with no IO or
regridding. Parameter file attached.</li>
<li>Run speeds are measured from Carpet::physical_time_per_hour at
iteration 256. <br>
</li>
<li>I tried both with and without hwloc/SystemTopology.<br>
</li>
<li>For both McLachlan and LazEv, I see similar results, with 2
MPI/node giving the worst results (see attached plot for
McLachlan) and a slight preferences for 8 MPI/node.<br>
</li>
</ol>
<p>So my questions are:</p>
<ol>
<li>Has there been any tests run by any other users on stampede2
skx?<br>
</li>
<li>Should we expect 2 MPI/node to be the optimal choice? <br>
</li>
<li>If so, are there any other configurations we can try that
could help optimize?</li>
</ol>
<p>Thanks in advance!</p>
<p>Jim Healy</p>
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