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single i7 MUCH faster than dual xeon E5-2650 v3 !!! |
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December 14, 2014, 06:24 |
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#1 | ||||||||||||
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,975
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Greetings to all!
I'll be trying to answer on this post the questions posed by acasas and by Chris Lee: @acasas: Quote:
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The essential concept is that you have to think that mores cores will be running slower, but they will also be responsible for lesser RAM to be crunched. Then you have to take into account for the total available memory bandwidth. Beyond that, it starts depending on the complexity of your case... this to say that in some crazy situations, overscheduling a 12 core machine with 18-36 processes might provide results slightly faster, because of an alignment in memory accesses. Quote:
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OpenFOAM xeon benchmark there you might find that a system with 12 cores @ 2.5GHz that costs roughly 1000 USD gives a better bang-for-your-buck than 8 cores @ 3.9 GHz that cost 2000 USD (not sure of the exact values). But the 8 core system gives the optimum performance of RAM bandwidth and core efficiency, but the 12 core system costs a lot less and spends a lot less in electrical power consumption, while running only at 76% CPU compute performance of the 8 core system. In such a case, you might want to weigh in an additional and very important factor: how fast do you want your meshes to be generated, if they can only be generated in serial mode, not in parallel? Quote:
For comparison, the i7-4960X with 6 cores would be using 32 GB, with 5.33 GB per core at roughly 9.95 GB/s. Now that I look more closely at the 3 CPUs you proposed for comparison, the only major difference is:
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And don't forget about the time it takes to generate the mesh, when using a CPU that has more cores, but less top speed when running in single core. ------------------- @acasas: Quote:
Best regards, Bruno |
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January 13, 2015, 12:58 |
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#2 |
Member
Antonio Casas
Join Date: May 2013
Location: world
Posts: 85
Rep Power: 13 |
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January 15, 2015, 04:58 |
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#3 |
Member
Antonio Casas
Join Date: May 2013
Location: world
Posts: 85
Rep Power: 13 |
Hi guys, I came up with some results over, what from now on I would like to call the "Erik´s Benchmark" , wich you can find at http://www.cfd-online.com/Forums/har...quad-xeon.html
Model: Geometry: 1m x 1m x 5m long duct Mesh: 100 x 100 x 500 "cubes" all 1x1x1cm (5M cells) Flow: Default Water enters @ 10m/s at 300K, goes out other side at 0Pa. Walls are 400K. High Resolution Turbulence and advection Everything else default. Double Precision: ON 20 iterations (you must reduce your convergence criteria or it will converge in less iterations.) I did perform the "Erik´s Benchmark" over a single i7 3820 and over a dual xeon E5-2650 v3, both under Windows 7 Pro 64 bits On the i7 3820 @ 3.6 Ghz and DDR3 SDRAM PC·-12800 @ 800 MHZ, with 4 real cores and 8 threads, and with affinity fully set, it took 1598 sec wall time. On the dual Xeon E5-2650 v3, 20 real cores, no hyper threading, overclocking on, RAM memory DDR4-2133 (1066 MHz), it took 533 sec wall time. On the dual Xeon for other amount of cores, affinity was not automatically set, so the run time wouldn´t be useful for this benchmark comparison. In some cases the computer was almost not doing any progress until I did set manually the affinity for every single core on the task manager for the "solver-pcmpi.exe" tasks. If any of you guys, would like I do run this "Erik´s Benchmark" over my dual Xeon for any other amount of cores than 20, and post in here the results, please, could you explain how to establish or set the affinity "in advanced" before running the test. Is there any way to program or define the affinity for the solver-pcmpi.exe in advance? thank´s a lot |
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