Has Bare Feats helped you? How about donating to Bare Feats?

BARE FEATS LAB - real world Mac speed tests

iMac Pro with FOUR GPUs!

August 16th, 2019 by rob-ART morgan, mad scientist
Correction August 20th: Blender renders using OpenCL.

We connected THREE eGPUs to the iMac Pro. How fast can GPU intensive apps run when all four GPUs are 'cooking'?

V64+VegaF+Dual VII = Radeon Pro Vega 64 GPU + Radeon Vega Frontier Edition GPU+ dual AMD Radeon VII GPUs
V64 + Dual VII = Radeon Pro Vega 64 GPU + dual AMD Radeon VII GPUs
Dual VII = Dual Radeon VII GPUs
Vega64 + VII = Radeon Pro Vega 64 GPU + Radeon VII GPU
Radeon VII = one Radeon VII GPU
Pro Vega 64 = Radeon Pro Vega 64 GPU

TEST MULE: 2017 iMac Pro 8-core 3.2GHz Xeon W-2140B, 32GB of 2666MHz DDR4 ECC memory, Internal Radeon Pro Vega 64 (16GB HBM2) GPU, 1TB PCIe-based flash storage. The Vega and VII GPUs were installed in eGPU Boxes and connected to the iMac Pro's Thunderbolt 3 Ports.


Rendered the BMW (bmw27_gpu.blend) demo scene using only GPU(s) redering using OpenCL. (LOWER time in seconds = FASTER.)

Blender benchmark showing eGPU effect on 2013 Mac Pro


Three Nodes of Noise Reduction was applied to the Candle Project "Parrot" clip. The GPU intensive effect is rendered on the fly using Metal during looping playback. (HIGHER frames per second = FASTER.)

DaVinci Resolve showing eGPU effect on 2013 Mac Pro


Though the optional factory AMD Radeon Pro Vega 64 is powerful, we wanted to show how the iMac Pro can benefit from adding eGPUs with even more powerful GPUs. We chose tests that fully stress the GPU (and that can use all available).

The beauty of Blender and DaVinci Resolve is that they give you full control of what GPUs will be used for rendering. And they don't require additional displays to take advantage of the external GPUs. Blender renders with OpenCL. Resolve gives you the choice of Metal and OpenCL.

Not every pro app takes advantage of multiple GPUs -- especially if they are external. Not all let you choose the active GPU(s). Not every app makes good use of GPUs. And each model of Mac reacts differently to the presence of eGPUs. It is a mixed bag so you must experiment. But then nobody wants to invest in faster GPUs with or without eGPU boxes without knowing the benefits or lack thereof. A chart would be helpful. I'll get started on it.

We hesitated to add the Vega Frontier as a third eGPU box since it is forced to share a Thunderbolt 3 controller with the eGPU box connected to the adjacent Thunderbolt 3 port. (The iMac Pro has four Thunderbolt 3 ports, each pair sharing a controller.) If two GPUs using a shared controller saturate the bandwidth, the performance gain can be limited. It's probably best to stick with just two eGPUs on the iMac Pro -- one on each Thunderbolt 3 controller. Ditto for the recent models of iMac, MacBook Pro, Mac mini with four Thunderbolt 3 ports.

As for eGPU boxes, we used a mix: AKiTiO Node Pro (500W), Sonnet Breakaway eGFX (650W), and OWC Mercury Helios FX (650W). They handled the Vega Frontier and VII GPUs -- each with 300W TDP.

Comments? Suggestions? Feel free to email me, Follow me on Twitter @barefeats.

USA readers can help BareFeats earn a commission by
clicking THIS TEXT LINK or on any of our Apple display ads when considering a purchase.

Readers in Australia can support us by clicking our link to the Apple Store AU.

Trans International sells Mac memory and other Mac upgrades.

Other World Computing sells Mac memory, storage, eGPUs, and used Macs.

B&H Photo Video sells Apple products, GPUs, eGPUs, displays, storage, etc.

BARE FEATS LAB - 75th Birthday Donations for Rob-ART

Has Bare Feats helped you? How about helping Bare Feats?

copyright 2019 Rob Art Morgan
"BARE facts on Macintosh speed FEATS"