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The processor in the IBM BG/Q is actually a POWER A2.[1] I never
understood why Top500 listed them as BQC. The POWER A2 processor
actually has 18 cores: 16 for computations, 1 for the OS itself, and
1 'spare'. I believe the spare is not a hot spare, but is there to
increase the yield in chip manufacturing. If there are 18 usable
cores on the chip, one is disabled. If one core is not usable, well,
they still have the 17 they were hoping for. (This is what I heard,
but I don't remember who the source was or how credible it was. If
this is wrong, someone please correct me!). <br>
<br>
I wouldn't core the for the OS redundant. It actually improves the
performance of the total system, as documented by the well-known
'ASCI Q' paper [2]. <br>
<br>
Now to answer your question, the answer is yes. I highly recommend
you read [2] for a good explanation of why (the authors did a better
job explaining it than I can in a quick e-mail). However, the
improvement in performance increases with the size of the cluster,
so it probably won't be noticeable on small clusters. <br>
<br>
In addition to dedicating a single core for the OS, you also want to
reduce OS 'noise' (also called 'jitter') as much as possible by
reducing services on the head node. You can do this by turning off
or uninstalling unnecessary services and building a custom kernel
that has only the services and hardware support needed by your
cluster. This is the idea being the very minimal kernel compute-node
kernel (CNK) of the Blue Gene Nodes. This is an active area of
research with many different groups working in this area: <br>
<br>
<a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Lightweight_Kernel_Operating_System">https://en.wikipedia.org/wiki/Lightweight_Kernel_Operating_System</a><br>
<a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Compute_Node_Linux">https://en.wikipedia.org/wiki/Compute_Node_Linux</a><br>
<a class="moz-txt-link-freetext" href="http://www.mcs.anl.gov/research/projects/zeptoos/">http://www.mcs.anl.gov/research/projects/zeptoos/</a><br>
<a class="moz-txt-link-freetext" href="http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=323279">http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=323279</a><br>
<br>
[1]
<a class="moz-txt-link-freetext" href="http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?subtype=SP&infotype=PM&appname=STGE_DC_DC_USEN&htmlfid=DCD12345USEN&attachment=DCD12345USEN.PDF">http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?subtype=SP&infotype=PM&appname=STGE_DC_DC_USEN&htmlfid=DCD12345USEN&attachment=DCD12345USEN.PDF</a><br>
<br>
[2] <a class="moz-txt-link-freetext" href="http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1592958">http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1592958</a><br>
<br>
<br>
<pre class="moz-signature" cols="72">Prentice Bisbal
Systems Programmer/Administrator
Office of Instructional and Research Technology
Rutgers University
<a class="moz-txt-link-freetext" href="http://oirt.rutgers.edu">http://oirt.rutgers.edu</a></pre>
<div class="moz-cite-prefix">On 08/03/2015 05:06 AM, Mikhail
Kuzminsky wrote:<br>
</div>
<blockquote cite="mid:1438592787.955484558@f398.i.mail.ru"
type="cite">
New special supercomputer microprocessors (like IBM Power BQC and
Fujitsu SPARC64 XIfx) have 2**N +2 cores (N=4 for 1st, N=5 for
2nd), where 2 last cores are redundant, not for computations, but
only for other work w/Linux or even for replacing of failed
computational core.<br>
<br>
Current Intel Haswell E5 v3 may also have 18 = 2**4 +2 cores. Is
there some sense to try POWER BQC or SPARC64 XIfx ideas (not
exactly), and use only 16 Haswell cores for parallel computations
? If the answer is "yes", then how to use this way under Linux ?<br>
<br>
Mikhail Kuzminsky, <br>
Zelinsky Institute of Organic Chemistry RAS,<br>
Moscow<br>
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