[dominicafonso]

I'm facing a number of options around the 4-8 core, ~48GB RAM range and would appreciate some advice. Due to licensing costs and limitations we are running current release Star-CCM+ on only 4 cores.



While I've read in to the benefits of a high memory bandwidth, I wonder if this is irrelevant at low core counts on modern systems and more focus should be on cpu and memory speed.



The options I see available are:


Consumer grade

Ryzen 5 5600X (£350) - 6 core, 3.7GHz, 6x512KB L2, 1x32MB L3, ECC Memory - NO, Memory Channels 2, Memory bandwidth 48GB/s, Memory speed 3200MHz, Memory configuration required for 100% channel usage 2x16GB (Dual ranked) or 4x8GB (Single ranked). 4 ranks improves performance in certain applications, despite not increasing bandwidth (sorry for the gaming reference https://www.techspot.com/article/197...er-for-gaming/)



Workstation (1P) grade
EPYC 7232P (£580) - 8 core, 3.1GHz, 8x512KB L2, 2x16MB L3, ECC Memory -YES, Memory Channels 4, Memory bandwidth 95GB/s, Memory speed 3200MHz, Memory configuration required for 100% channel usage 4x8GB. Do memory ranks have any impact on EPYC performance?


Server (1P/2P) grade

EPYC 7262 (£600) - 8 core, 3.2GHz, 8x512KB L2, 8x16MB L3, ECC Memory -YES, Memory Channels 8, Memory bandwidth 190GB/s, Memory speed 3200MHz, Memory configuration required for 100% channel usage 8x8GB. Do memory ranks have any impact on EPYC performance?


Some observations on these builds. The Ryzen based system is comfortably the cheapest due to cpu and motherboard prices and brings the highest CPU speed and lowest memory configuration. There is also a shared 32MB L3 cache, is that benefit as each core can access all 32MB?



The 1P EPYC doubles the memory bandwidth for no increase in memory allocation/price (4 sticks) but loses 16% on cpu clock speed. The L3 cache comes in 2 shared blocks of 16MB each.


Finally, probably the textbook solution, the EPYC 7262 has the highest price tag and the most memory channels available. 8 sticks of ram would be required to take advantage of the memory channels though so that would double the memory cost as 8x4GB doesn't seem to be an option. Each core gets 16MB of L3 cache which is a big upgrade.


The price difference between the 2 extremes would cover the license cost of running on more cores, so for the same budget the options are Ryzen with 6 licenses or EPYC with 4 licenses.


Any advice on these or other configurations would be appreciated.

[flotus1]

Comparing Zen2 and Zen3 architectures based on specs like core frequency and cache size won't be very helpful. And is no longer necessary, since Epyc Milan has already been launched. You can't buy single CPUs yet, but the larger OEMs should be able to ship systems rather soon.
The absolute best choice for your requirements is the EPYC 72F3. Or if you absolutely have to save money on the CPU: EPYC 7313P

If you can not or do not want to run memory at higher transfer rates, getting 2 ranks per channel is always the better option. Regardless of the platform.

With licenses for only 4 threads, and a very limited budget, I would probably still choose Intels X299 lineup. They are slower than AMDs Zen3 Ryzen CPUs in single-threaded tasks, but quickly overtake them with better scaling in memory intensive applications. Buying a Ryzen CPU and investing in more parallel licenses probably won't pay off.

[dominicafonso]

Originally Posted by flotus1

Comparing Zen2 and Zen3 architectures based on specs like core frequency and cache size won't be very helpful. And is no longer necessary, since Epyc Milan has already been launched. You can't buy single CPUs yet, but the larger OEMs should be able to ship systems rather soon.
The absolute best choice for your requirements is the EPYC 72F3. Or if you absolutely have to save money on the CPU: EPYC 7313P

If you can not or do not want to run memory at higher transfer rates, getting 2 ranks per channel is always the better option. Regardless of the platform.

With licenses for only 4 threads, and a very limited budget, I would probably still choose Intels X299 lineup. They are slower than AMDs Zen3 Ryzen CPUs in single-threaded tasks, but quickly overtake them with better scaling in memory intensive applications. Buying a Ryzen CPU and investing in more parallel licenses probably won't pay off.

Thanks for your time on this. I think I see where you are coming from but I don't think the budget is there for your recommendations. X299 seems to be on a par with epyc Rome for price and according to the chart on your hardware wip thread slightly slower than the ryzn 5600x at 4 cores, so I'm surprised by your preference.

At the £1000 mark I feel I'll get the best performance from a ryzen 5600x and am struggling for alternatives. The question is, what is the next price point that delivers a significant performance gain at 4 cores? From what I have seen, a £2000 system really needs 6-8 licenses to be justified.

[flotus1]

The results reported in our little OpenFOAM benchmarking thread have to be taken with a grain of salt. They were run by different people with varying degrees of diligence. The benchmark spans several versions of OpenFOAM, and each of them may be compiled differently. A plethora of operating systems was used. And most of the time, there is only one data point for a specific hardware configuration.
For the Ryzen 5 5600x results in particular: they were achieved with elaborate manual optimizations for memory timings and frequency. Hence the disclaimer I put in the chart. If I had to guess, there was probably an overclock involved too. OP did not specify.

Long story short: if you don't want to jump through these hoops (or maybe the importance of your work doesn't allow it) your out-of-the-box results with a Ryzen 5 5600x will be slower.

As for the prices: An I7-9800x with 8 cores can be had for 350€ new retail. Which is pretty close to retail prices of a Ryzen 5 5600x.

[dominicafonso]

OK, I'll try to keep that all in mind.

I haven't found that chip widely available and the x299 motherboards seems to be at least £100 more than the ryzen options. I'll do some more searching though.

Thanks for your time.

[flotus1]

Last time I checked prices, X299 boards could be had for a more reasonable 150€ upwards. No idea what happened that suddenly made them so expensive. Maybe the overall shortage in some PC components spilled over to this market segment

I wish the choice for "the best" platform for your requirements was more clear cut. But it just isn't. Yet that also means that you won't make a huge mistake choosing either of them, at least for 4 cores.
Maybe throw some pre- and post-processing into the mix to make the decision easier. These don't scale as well as the solvers do, creating a strong argument for the CPU with higher single-threaded performance.

[dominicafonso]

This is where I have settled. I've aimed for the fastest possible 4 cores without an abundance of redundant cores. I'm hoping the memory performance scaling shown here OpenFOAM benchmarks on various hardware continues at higher memory speeds.
The motherboard and psu are mid range and the gpu is entry level.

I wish I could buy prebuilt without a case!

Case
CORSAIR 175R RGB MID TOWER GAMING CASE
Processor (CPU)
AMD Ryzen 5 3600XT Six Core CPU (3.8GHz/35MB CACHE/AM4)
Motherboard
ASUS® TUF GAMING B550-PLUS (DDR4, USB 3.2, 6Gb/s) - ARGB Ready!
Memory (RAM)
32GB Corsair VENGEANCE DDR4 3600MHz (4 x 8GB)
Graphics Card
2GB NVIDIA GEFORCE GT 1030
1st M.2 SSD Drive
512GB INTEL® 660p M.2 NVMe PCIe SSD (up to 1500MB/sR | 1000MB/sW)
Power Supply
CORSAIR 550W TXm SERIES™ SEMI-MODULAR 80 PLUS® GOLD, ULTRA QUIET

Operating System
NO OPERATING SYSTEM REQUIRED

Price: £897.00 including VAT and Delivery

[flotus1]

There is quite the difference in performance between a Ryzen 5 3600XT and a Ryzen 5 5600x. And a Ryzen 5 3600XT is just a more expensive 3600.

[dominicafonso]

Originally Posted by flotus1

There is quite the difference in performance between a Ryzen 5 3600XT and a Ryzen 5 5600x. And a Ryzen 5 3600XT is just a more expensive 3600.

I saw the 3600XT with a higher clock speed and lower price and thought I was on to a winner. I also assumed the 5600x had a higher price due to being new and not necesssarily its performance. I can knock a bit out of the motherboard at the cost of losing support for >3200MHz RAM and the gpu can be swap to make way for the the 5600x


Case
CORSAIR 175R RGB MID TOWER GAMING CASE
Processor (CPU)
AMD Ryzen 5 5600X Six Core CPU (3.7GHz-4.6GHz/35MB CACHE/AM4)
Motherboard
ASUS® PRIME B450-PLUS (DDR4, USB 3.1, 6Gb/s) - RGB Ready!
Memory (RAM)
32GB Corsair VENGEANCE DDR4 3600MHz (2 x 16GB)
Graphics Card
1GB NVIDIA GEFORCE GT 730 - DVI, HDMI, VGA
1st M.2 SSD Drive
512GB INTEL® 660p M.2 NVMe PCIe SSD (up to 1500MB/sR | 1000MB/sW)
Power Supply
CORSAIR 550W TXm SERIES™ SEMI-MODULAR 80 PLUS® GOLD, ULTRA QUIET


Processor Cooling
STANDARD AMD CPU COOLER

Operating System
NO OPERATING SYSTEM REQUIRED

Price: £893.00 including VAT and Delivery

[Simbelmynë]

So as Flotus1 has already pointed out, in order to achieve the results seen in the OF benchmarking thread with Zen2/Zen3, you will probably need to manually adjust the timings of your memory. In order to hit maximum performance you need good memory that can handle low latencies at 3600 MHz. With Zen 3 you may be able to push it even further to about 4000 MHz 1:1 ratio with the infinity fabric, but there may (or may not) be some serious diminishing returns at that stage. I would look at memory that can handle 3600 MHz @ CL 16 at the very minimum.



A 1 GB VRAM GPU is not something I would settle on. 4 GB cards should be attainable on the used market since Ethereum has gone beyond 4 GB for some time now.