[wildfire230]

Hi all,


I'm looking to build a general purpose workstation that can double as a bit of a powerhouse for OpenFOAM CFD simulations. Could you please take a quick look at my build details and let me know if everything makes sense? I wanted to keep it below $5k. I wanted to get a lot of cores, but still keep the single core speed quite high, since this will also be a general purpose office machine, so I settled on the i9-9920x, which has 12 cores, quad-channel memory capable, single core base speed 3.5 GHz, up to 128 GB DDR4-2666. Does this seem like a logical choice? For OpenFOAM you want the number of cores to be an integer multiple of the number of memory channels for maximum parallel speed up, correct?


Here is a link to the part list: https://pcpartpicker.com/list/7cd9jy


Or here are the parts written out:


Intel Core i9-9920x 3.5 GHz 12-Core Processor
Corsair H150i PRO Liquid CPU Cooler
EVGA X299 FTW K EATX LGA2066 Motherboard
Corsair Vengeance LPX 128 GB (8 x 16 GB) DDR4-2666 Memory
Samsung 970 Evo 1 TB M.2-2280 NVME Solid State Drive (For the OS)
MSI GeForce GTX 1660 6 GB Gaming X Video Card
Corsair 760T Black ATX Full Tower Case
Corsair 1000 W 80+ Platinum Certified Fully Modular ATX Power Supply


I don't have any specific needs for a super powerful gpu, but I may end up running dual 1440p monitors, and I thought the GeForce GTX 1660 could handle that.


If anyone has any critiques or feedback it would be greatly appreciated!


Thanks

[flotus1]

For OpenFOAM you want the number of cores to be an integer multiple of the number of memory channels for maximum parallel speed up, correct?

No idea where you got that from, but no. The thing worth keeping in mind is that you won't see much benefit with more than ~3 cores per memory channel, as a general rule of thumb. So buying an expensive 18-core CPU with only 4 memory channels is not a good use of budget for a CFD machine. It doesn't matter at all whether the ratio is an integer or not.

The build looks reasonable overall, but of course I have a few nitpicks:
1) The power supply could easily be downsized to save some cash, at least for the current configuration. It won't need more than a 600W PSU of decent quality.
2) and most importantly: get faster RAM...like much faster. In fact, the fastest you can comfortably afford.
Not 100% sure about the prices overseas, but here I can buy 16GB DIMMs of DDR4-3600 starting at 85€ including tax. More like 110€/16GB if you want CL16 out of the box. If this sounds too expensive, maybe reconsider if you need 128GB straight away or could start with 4x16GB instead? What are you going to do with it that requires this amount of RAM?

A word of warning: rumor has it that AMD will release new Threadripper CPUs based on Epyc ROME towards the end of 2019. Based on the alleged specifications, it is safe to assume that it will wipe the floor with anything Intel has to offer in the HEDT market. Even if it should not have the full 8 memory channels, it would still be a better option than X299. So if you don't absolutely need the workstation right now, waiting until the end of the year would be a good idea to avoid buyers remorse.

[wildfire230]

Hi Alex,


Thanks for the feedback. Is it alright to use faster ram? The specs on the i9-9920x show that it supports DDR4-2666. I was under the impression this was the upper limit in terms of speed for the processor.


Thanks again

[flotus1]

It is the lower limit that Intel guarantees to run, and a very conservative estimate. These CPUs can run RAM a lot faster than this. When X299 was introduced, Some motherboard manufacturers showcased 128GB of DDR4-4000.

[wildfire230]

Thanks again. So how can you practically identify the upper limit on ram speed? Is it a limit of the motherboard?


One other quick question, how important is the CAS latency for OpenFOAM performance? I'm seeing DDR4-3600 kits at C18.

[flotus1]

No, the upper limit depends on the individual CPU, since it technically is overclocking. And on the type of motherboard. Here EVGA is probably a safe choice.
Spending vast amounts more money on low latency memory is probably usually the best use of money. DDR4-3600 with CL18 is fine if CL16 would 20% more. Memory prices are pretty volatile, so making a definitive recommendation is difficult. If you want to optimize further, you can still do manual overclocking.