<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Christoph<div class=""><br class=""></div><div class="">Some answers to your questions. But there are more knowledgable people out there!</div><div class=""><br class=""></div><div class="">The MITgcm scales well and is routinely run on thousands of cores. </div><div class="">example:</div><div class=""><a href="https://people.nas.nasa.gov/~chenze/ECCO/SC05/ecco_sc05.pdf" class="">https://people.nas.nasa.gov/~chenze/ECCO/SC05/ecco_sc05.pdf</a></div><div class=""><br class=""></div><div class="">(Obviously if you try to run a small model domain on many cores it will be inefficient.)</div><div class=""><br class=""></div><div class=""><div>In my experience with forward model runs <font face="Verdana" class="">memory isn’t a bottleneck. </font></div><div><br class=""></div><div>I am not sure what size runs you are talking about, but for runs with great than a few hundred cores I think the bottleneck is primarily with the interconnects and I/O to the NFS. Hopefully people will correct me if I am wrong. </div><div><br class=""></div><div>Matt</div><div><br class=""></div><div><blockquote type="cite" class=""><div class="">On Apr 9, 2019, at 6:13 AM, Christoph Stappert <<a href="mailto:cstappert@gmx.de" class="">cstappert@gmx.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><div style="font-family: Verdana;font-size: 12.0px;" class=""><div class="">Hello everyone,</div>
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<div class="">I am currently building a workstation to run some MITgcm simulations, and I am wondering which of the different CPU models I am considering would be best suited for the task:</div>
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<div class="">Ryzen 7 1700 (8x 3.0 GHz, dual-channel RAM): A consumer-grade CPU and siginificantly cheaper than the others. However, while it does have ECC, the ECC feature is not officially supported by AMD, so I am reluctant to use this CPU in scientific computing.</div>
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<div class="">Xeon E-2146G (6x 3.5 GHz, dual-channel RAM): This is the option I am leaning towards at the moment.</div>
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<div class="">Ryzen Threadripper 1950X (16x 3.4 GHz, quad-channel RAM): More CPU cores than the other two options, but also more expesive. I am wondering, how big would the performance gain actually be in practice?</div>
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<div class="">I have read in some messages on this list that MITgcm does not scale well with an increasing number of CPU cores and that memory bandwidth is an issue. However, these messages were more than 10 years old, so I am not sure if this still applies to the latest generation of CPUs and to the latest version of the software. I was not able to find any newer messages on hardware recommendations, performance and such.</div>
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<div class="">My specific questions are:</div>
<div class="">- How well does MITgcm scale with an increasing number of CPU cores (4, 8, 16, 32...)? At which point would I stop seeing a significant increase in performance?</div>
<div class="">- Is there a bottleneck with memory bandwidth in today's CPUs? Does a higher number of RAM channels significantly increase performance?</div>
<div class="">- Are L2 cache and L3 cache a major bottleneck?</div>
<div class="">- Does MITgcm benefit from using AVX-512 or other Intel-specific features (since AMD hasn't really been a factor in scientific computing in the last couple of years)?</div>
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<div class="">Of course, I could just get all the CPU models under consideration and do my own benchmarks, but unforunately, I do not currently have the budget or the time for this. So I was hoping that someone here might have some insights based on their knowledge of the MITgcm code or some personal experience using different kinds of hardware.</div>
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<div class="">Thank you and kind regards,</div>
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<div class="">Christoph</div>
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