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8-12 core workstation for Star CCM+

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Old   March 14, 2019, 09:44
Question 8-12 core workstation for Star CCM+
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Hello,

I am currently looking to buy/build a workstation for Star CCM+, and was hoping to get a little advice.

Background: We will not upgrade our licenses before early 2020. We already have a 16 core machine which works quite well - we would like to have one more workstation, but only have 8 cores worth of licenses left for this machine. We could go with something like 12 cores and then re-allocate licenses from existing machine, but this might not be very cost effective.
Current workstation is running 2xE5-2630 v3 (8cores 2.4 Ghz 20 mb cache).

The budget is ~5000-6000 euro for the entire workstation.

Aside from CPU, we need 250 GB SSD + 8 TB HD for data storage and a basic GPU.

I am currently considering:
1) AMD Epyc 7251 single CPU (8 cores, 2.1 GHz, 32 MB cache)
2) Intel Xeon Gold 6134 Skylake SP (8 cores, 3.2 Ghz, 24.75 MB cache)
My gut feeling is that I would get more speed with the Gold 6134, even though there's less memory bandwidth.

I am very open for suggestions!

BR
/Henrik
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Old   March 14, 2019, 14:41
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AMD Epyc 7371 is by far the best CFD workstation CPU.
It has 8 memory channels and is currently the highest frequency 16-core CPU. With a price of around 1700$ it should fit comfortably into your budget.
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Old   March 14, 2019, 15:09
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Thanks Flotus. Markes total sense to go for high clockspeed AND high bandwidth.

In a single CPU motherboard using 8x8GB of ram, would I take full advantage of the CPU even when running only E.g. 8 or 12 cof the 16 cores?

BR
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Old   March 14, 2019, 15:10
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AMD Epyc 7261 is the fastest 8 core AMD processor. The lowest frequency is 2.5 GHz and it got 64 MB cache. You should choose that over the 7251.
I don’t know if it will be faster than the Intel alternative for you usage.

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Old   March 14, 2019, 15:18
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Quote:
Originally Posted by HBH_aero View Post
In a single CPU motherboard using 8x8GB of ram, would I take full advantage of the CPU even when running only E.g. 8 or 12 cof the 16 cores?
Definitely. You just have to make sure the threads are evenly distributed across the 4 NUMA nodes. But that should be the default behavior anyway.
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Old   March 14, 2019, 16:46
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Quote:
Originally Posted by HBH_aero View Post
In a single CPU motherboard using 8x8GB of ram, would I take full advantage of the CPU even when running only E.g. 8 or 12 cof the 16 cores?

BR
Henrik

Not sure I understand the question. If you have 16 cores on your single EPYC CPU, then you will see improved results up to 16 cores. So no, you would not take full advantage of the CPU.



On the contrary a 8700k will only benefit from 4 of the 6 cores for CFD, at least when 3200 MHz memory is used. Or put in a different way - The 8700k is memory bottle-necked above 4 cores (there is definitely more CPU power available, but it cannot be used).


(the above analysis is based on the motorbike benchmark, so it may vary depending on your application)
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Old   March 14, 2019, 17:04
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In this context, making full use of the CPU means getting the maximum possible performance out of those 8 licenses.
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Old   March 15, 2019, 02:05
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Ah, ok I see, then I guess the 12 cores OP mentiones is 8+4 licenses. At least for us, ANSYS provides the option to run on 4 cores for each serial license, so it then makes sense.
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Old   March 15, 2019, 03:36
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Hi Simbelmynė,

The license system from Siemens for Star CCM+ is a little complicated. We have a total of 18 cores distributed on 2 solver jobs. We already have an 'old' machine running up to 16 cores. So I am looking to employ 8-12 cores on this new workstation. As Flotus said, what I mean by 'full advantage' is basically whether I would see pretty linear scale-up from 8 to 16 cores on an Epyc 7371.

I will update this thread in a week or so, when I have a suggestion for a full workstation :-) .

I guess I should go for dual channel 2666 MHz ram?
Do I have the freedom to go for a motherboard with 2 CPU 'slots' so that I could upgrade my machine later on?

Thank you all - I don't know how I would have approached this without a forum like this.
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Old   March 15, 2019, 13:04
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Quote:
what I mean by 'full advantage' is basically whether I would see pretty linear scale-up from 8 to 16 cores on an Epyc 7371
That would be a bit of a stretch. Scaling will definitely not be linear beyond 8-12 cores. But there is currently no single-CPU that will get you closer than this one.
Apart from a lower-clocked 16-core Epyc CPU. Due to the lower performance per core, scaling in bandwidth-intensive applications will be better. But of course overall performance would be worse
For (super-)linear scaling up to 16 threads you would need 2 of these CPUs.

Quote:
I guess I should go for dual channel 2666 MHz ram?
Dual-ranked would be ideal.

Quote:
Do I have the freedom to go for a motherboard with 2 CPU 'slots' so that I could upgrade my machine later on?
That would be a very good idea, I'd recommend that.
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Old   March 15, 2019, 14:30
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For bandwith intensive applications combined with an expensive license, it could be a good option to distribute the load over two cpu’s and then get 16 memory channels. Even with just 8 to 12 active cores two Epyc 7261 would be faster than one 7371 for such applications, but not as fast as two 7371.
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Old   March 18, 2019, 12:09
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Hi all,

So, I have been in touch with a few local retailers. Apparently the 7371 seems to out of stock everywhere (I am based in Denmark). I will most likely go forward with a 7261.

Ill update next week when I get a full workstation offer from a retailer :-)
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