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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Hi All,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">For those still interested in this thread, timing tests with MKL indicate that sequential MKL performs approximately the same as parallel MKL with NUM_THREADS=1,
which isn't too surprising. What is a bit surprising is that MKL always, at least for this application, gives significantly slower performance than direct compilation of the code from --download-f-blas-lapack=1. My conclusion is that if your code is written
with explicit parallelization, in this case using PETSc, and fully utilizes your hardware, using sophisticated libraries may actually harm performance. Keep it simple!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Now a question: all my tests used MPICH2. Does anyone think using Intel MPI would significantly improve the performance of MKL with PETSc?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Rob<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:
"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;
font-family:"Tahoma","sans-serif""> petsc-users-bounces@mcs.anl.gov [mailto:petsc-users-bounces@mcs.anl.gov]
<b>On Behalf Of </b>Rob Ellis<br>
<b>Sent:</b> Tuesday, March 15, 2011 3:33 PM<br>
<b>To:</b> 'PETSc users list'<br>
<b>Subject:</b> Re: [petsc-users] Building with MKL 10.3<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Yes, MKL_DYNAMIC was set to true. No, I haven't tested on Nehalem. I'm currently comparing sequential MKL with --download-f-blas-lapack=1.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">Rob<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:
"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;
font-family:"Tahoma","sans-serif""> petsc-users-bounces@mcs.anl.gov [mailto:petsc-users-bounces@mcs.anl.gov]
<b>On Behalf Of </b>Natarajan CS<br>
<b>Sent:</b> Tuesday, March 15, 2011 3:20 PM<br>
<b>To:</b> PETSc users list<br>
<b>Cc:</b> Robert Ellis<br>
<b>Subject:</b> Re: [petsc-users] Building with MKL 10.3<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks Eric and Rob.<br>
<br>
Indeed! Was MKL_DYNAMIC set to default (true)? It looks like using 1 thread per core (sequential MKL) is the right thing to do as baseline.<br>
I would think that the performance of #cores = num_mpi_processes * num_mkl_threads might be <= #cores = num_mpi_processes case (# cores const) unless some cache effects come into play (Not sure what, I would think the mkl installation should weed these issues
out).<o:p></o:p></p>
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<br>
P.S :<br>
Out of curiosity have you also tested your app on Nehalem? Any difference between Nehalem vs Westmere for similar bandwidth?<br>
<br>
On Tue, Mar 15, 2011 at 4:35 PM, Jed Brown <<a href="mailto:jed@59a2.org">jed@59a2.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Tue, Mar 15, 2011 at 22:30, Robert Ellis <<a href="mailto:Robert.Ellis@geosoft.com" target="_blank">Robert.Ellis@geosoft.com</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Regardless of setting the number of threads for MKL or OMP, the MKL performance was worse than simply using --download-f-blas-lapack=1.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Interesting. Does this statement include using just one thread, perhaps with a non-threaded MKL? Also, when you used threading, were you putting an MPI process on every core or were you making sure that you had enough cores for num_mpi_processes
* num_mkl_threads?<o:p></o:p></p>
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