Dual EPYC 7742s for 3D Rendering (part of a Render Farm)

jtabc

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Jul 31, 2022
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I do a lot of CPU rendering in Cinema 4D. I render 4K high-framerate animations, so they take a long time. Currently I have a bunch of mid 2010s laptops and a desktop hooked up and I use my own Python-based render manager to distribute workloads to each machine. Even with 7 laptops and the desktop, it's still not really fast enough for what I need to do (full animations typically take weeks or months to render).

I'm wanting as many cores as possible for as cheap as possible. While the new Threadripper 5995wx would have the best performance on its own, I cannot justify the $7,000 price.

I'm seeing a lot of AMD EPYC 7742s on Ebay for $2,000 or lower (not engineering/qualification samples). The supermicro motherboards, like this one or this one, are usually only around $400-$500.

I'm considering buying one or two of these since they should speed up my workload a lot, but what I don't understand is what kind of RAM I need, the frequency, and how much. The 3D rendering workload itself uses very little RAM, but my understanding is that the performance of these CPUs can be limited if not every DIMM slot on the motherboard is populated, and I've also heard that you should use higher rank RAM (at least dual rank) or the performance can be a lot worse.

I've seen a huge difference in Cinebench R23 scores, for example, for Dual 7742s in benchmarks online. I've seen some as low as 63,000, which is about what you'd expect with just a single 3990x, and some as high as 99,000. This is a big difference, especially if those are the speeds I would expect when running for a long period of time. I'm not sure what configurations could lead to such huge performance differences, but this is obviously important if I intend to buy and use these for Cinema 4D rendering.

Could somebody please provide some insight into what might be causing such a huge difference in those scores? I think it's related to RAM, but I'm not sure. If I were to buy two 7742s, what configuration of RAM would I need (rank, number of individual DIMMs, and frequency) to get the best performance?
 

MBastian

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Jul 17, 2016
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The performance of the older (Zen 1 and 2) CPUs do suffer if you do not provide each 8 core chiplet with its own local RAM. Also frequency is important as the memory clock is synchronized with the Infinity Fabric frequency. With Zen 3 AMD introduced a central memory controller. I'd advice to stay away from these old parts. For the price of one 7742, with motherboard and memory you could probably build three 5950X based render nodes, each having a R23 score of roundabout 24-29k. If you can wait a bit for the Zen 4 launch there should be some good bargains on Ebay when enthusiasts unload their old Zen3/DDR4 stuff.
 

RolloZ170

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Apr 24, 2016
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I've seen a huge difference in Cinebench R23 scores, for example, for Dual 7742s in benchmarks online
they do not scale like intel scalables. for that reason AMD build single processors with more&more cores....
i have tested 24Core Platinum CB R20 with only one 8GB RDIMM and 6x 8GB RDIMMs - there is no score difference, also dual conf. misses only 10%.
i don't want you to go to/with intel - but i.e. think about what MBastian say'd.
 

jtabc

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Jul 31, 2022
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The performance of the older (Zen 1 and 2) CPUs do suffer if you do not provide each 8 core chiplet with its own local RAM. Also frequency is important as the memory clock is synchronized with the Infinity Fabric frequency. With Zen 3 AMD introduced a central memory controller. I'd advice to stay away from these old parts. For the price of one 7742, with motherboard and memory you could probably build three 5950X based render nodes, each having a R23 score of roundabout 24-29k. If you can wait a bit for the Zen 4 launch there should be some good bargains on Ebay when enthusiasts unload their old Zen3/DDR4 stuff.
To make sure I'm understanding, what you're saying is that for Milan CPUs (such as the 7763), you could get away with fewer sticks of RAM without impacting performance than you can for Rome (like the 7742)?

The reason I'm hesitant to build several smaller systems like several 5950x machines is that I think the overall efficiency would be a lot lower since so many independent systems would draw more power for a given level of performance (you would have multiple motherboards and coolers that you would only have one of with a 64 core chip).
 

Spartus

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I've also heard that Cinebench really doesn't scale well to 256 threads so it might be under-representing what dual 64 core CPUs are capable of compared to a bunch of smaller systems.
 

RolloZ170

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Apr 24, 2016
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with Milan only 6 DIMM - you get 75% of bandwidth, with Rome less(50..
you could get away with fewer sticks of RAM without impacting performance than you can for Rome (like the 7742)?
with 6 instead of 8 DIMMs you would expect 75% of bandwidth...right for 7003, not if you have 7002(rome)
 

mirrormax

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Apr 10, 2020
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You want 8dimms, dual rank 3200 ecc.
for cpu get the QS 7742 rome, or 7763 milans, first ones are down in price again to around 2k now and they are basically unlocked retail cpus, and ive seen the milans for 2500$ i think but havnt tested those nor seen anyone else on here.
scores vary widely based on bios settings, cooling and motherboard. ive done 100k with dual 7742, but thats with a custom watercooled setup and overclocked(QS are overclockable)
around 80-84k is more common.
but if you can do 2 or more renders at once you can split them up between the cpus and get the full 100% scaling without the penalty of cross cpu latency.
 

Sean Ho

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I assume this is only for the rendering, and you already have a workstation for modelling? Would you consider Redshift or Octane and (possibly multiple) GPU rendering?
 

bayleyw

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Jan 8, 2014
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Pricing-wise, I think the sweet spot for used RDIMMs is 2400MHz, which you can usually run at 2666MHz (Supermicro boards, at least, let you pick your RAM speed up to the maximum supported by the CPU).
As I was just saying here, you get really weird pathologies with suboptimal memory population on Rome, so its not really worth doing anything other than 8 DIMMs per socket. CB wasn't one of the impacted programs (I got about 49K regardless of memory configuration on a 1P 64c @2.5GHz), but its really just not worth dealing with any possible performance regressions.
The first image you posted is not a 7742, it is a weird pre-release 77xx engineering sample with an unlocked multiplier and a really low power limit.

@MBastian also has a fair point: if you are rendering animations where each frame fits in 64GB, by far the cheapest route is a bunch of stock 5950X with 4x16 UDIMM and midrange boards. You don't even need a GPU, except for initial setup, if the farm runs remote. Because of how CB scales you really get diminishing returns after the first 32 cores, a 7742 is only twice as fast as a 5950X despite having four times the cores. The production rendering guys use TR Pro/Epyc because the norm in the high end rendering industry is to construct enormous scenes (hundreds of GB) - its cheaper to buy more RAM than to teach the artists how to deal with draw distances and level of detail.
 
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i386

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I'm seeing a lot of AMD EPYC 7742s on Ebay for $2,000 or lower (not engineering/qualification samples).
With used epyc and threadripper pro cpus you gotta be careful: they could be vendor locked and might not work with your mainboard(s)
 

NablaSquaredG

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If the CPU is cheap enough, it might be worth buying a Barebone from the vendor it was locked to ;)
 

i386

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dell, lenovo, hpe*... (semi) new barebones... cheap? :D

*sth updated the post about vendors locking their system with amd psb, seems that hpe uses something different
 

RolloZ170

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Apr 24, 2016
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dell, lenovo, hpe*... (semi) new barebones... cheap?
at least the Dell systemboards (R6415,R7415) are cheap(from $265..$599)
but the ebay scalpers ask the same for front-panel/PIB and other required stuff..:(