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Researching new build: Ryzen 9 3900x + X570 PCIe optimizations

Mike D

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Hey all,

Really love this site! It has helped me a great deal in catching up and understanding current tech. The last time I built a PC (from CyberPower) was 2012! Quarantine has got me bored and looking to update/learn new things, so here I am.

Primary use for this machine is experimentation and learning for motion graphics (professional by day, have a company machine for that) and also gaming. Mostly AE, C4D, Octane/Embergen, RS, Houdini, Xparticles.

I think I've settled on a Ryzen 9 3900x as the CPU with the X570 mobo. My main concern right now is about optimizations with the PCIE lanes. I'm still a little new to this area but ideally I'd like to use 2 GPUS + 1-2 NVME in this build. From my researching it seems that only the 2080 TI and future 3000 cards even get close to using full bandwidth of cards and support PCIE 4. And I definitely want the NVME drives using full bandwidth, right?

What is the optimal setup for these devices? And how much concern should I have if they are using x16 or x8? Does my software even benefit from PCIE 4 vs 3 or x16/x8? Any info would be great! Maybe I'm obsessing too much on this detail.

Thanks!
 

Alex Glawion

CG Hardware Specialist @ CGDirector
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Hey Mike,
All currently available Nvidia GPUs are a maximum of pcie3 so havin a pcie4 motherboard will make no difference at the moment. Upcoming gens of course might support pcie4. The 2080Ti really is the only gpu at the moment that barely saturates a pcie3 x8 bandwidth, but even still you can easily run it at x8 with no slowdowns in most cases. GPU rendering is something done on the gpu, optimally the entire scene is loaded into the vram and no communication over the pcie bus has to be made, so you won't notice a difference between x8 and x16 in most scenes on a 2080ti.

I meant to write an article on this with benchmarks as it is asked often.

There are pcie4 gpus from AMD, but you will not be able to use those until there is official amd support for octane (still being developed currently and not as fast as CUDA yet).

Same with nvme ssds. If you're buying a pcie3 nvme ssd (like a samsung 970 evo plus) then of course you won't benefit from the pcie4 bus - the ssd will run in pcie3 mode. There are some pcie4 nvmes on the market though, which are a lot faster in sequential read / write so you can make use of your pcie4 M.2 bus for nvme drives. That's sequential though. Other workloads, random, or mixed read / write is still about the same speed as pcie3 nvme ssds, because this is mostly not bandwidth related.

I'll have @Jerry James chime in here to correct me if I am wrong, but as far as I know, although you can use multiple pcie4 nvme drives on an x570 Motherboard (even in addition to 2 or more gpus) the chipset is attached to the cpu through a x4 pcie4 link, so if you're using both pcie4 nvmes at full speed, the DMA link will be the bottleneck.
 

Jerry James

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Hey Mike, on an X570 motherboard that has PCIe bifurcation (giving you 16 lanes split between two x8/x8 slots direct to the CPU) you have more than enough bandwidth left for storage.

On the X570 Unify, for example, you can easily run two GPUs and a single NVMe M.2 off of just CPU lanes without even bringing in the chipset into the equation yet. Coming to the chipset lanes, unlike other platforms, the chipset link on X570 is PCIe 4.0 x4, which means it has more than enough bandwidth to handle two additional M.2 NVMe drives without throttling.

Running two PCI 4.0 drives full-tilt using the bottom two slots (the ones using the chipset) is another story though. We'll have to test to be sure about how much, but writing huge chunks of data to two PCIe 4.0 drives at the same time should theoretically throttle because they'll be starved for bandwidth.

That said, if you want 2x GPUs and 3x NVMe drives, X570 is more than up to the task for 99% realistic workloads out there.
 

Mike D

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Thank you both so much for taking the time to look into that. I really appreciate it.

I actually was looking at the X570 Unify just yesterday, perfect timing. I think I'm zeroing in on my full build. I'll post the specs once I'm sure to get your guys' opinion/approval. 🙏
 
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