MacOS - Max number of GPUs
 
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highpass
(@highpass)
Eminent Member
Joined: 3 years ago
 

This isn't specifically eGPU related but I thought someone here might be able to answer.

Apparently recent versions of MacOS can only address 3 Nvidia GPUs + 1 AMD GPU. Is this true and can anyone elaborate on why?

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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Flint Ironstag
(@flint-ironstag)
Estimable Member
Joined: 3 years ago
 

This is probably due to the fact that no currently shipping Mac has traditional PCIe slots.  The limitation seems to be in the method (enumeration I understand it's called) of allocating resources to GPUs at boot time.  On TB equipped Macs, that limit seems to be 2 eGPUs.  1 per bus, 2 on the same bus in the same enclosure, doesn't matter.

Occasionally a thread pops up somewhere about using a cMP to drive massive video walls.  You might also check the Octane forums - a few years ago there were some cMP users stacking Nvidia cards in.  There's not a ton of info out there on the theoretical max.  At one point in the Mac Pro's lifespan, you could configure it with 4 GPUs from Apple.  Then Magma, CUBIX, etc. had the aftermarket PCIe expansion chassis.

If 4 GPUs is indeed the limit again, this will need to be addressed on mMP at least.

MP 6,1 | 4c | d700
MP 6,1 | 6c | d500


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highpass
(@highpass)
Eminent Member
Joined: 3 years ago
 

Hi Flint

As far as I can tell the history is thus:

Prior to 10.8/10.9, a cMP could run 5 total Nvidia GPUs (1 internal for boot, 4 in a Cubix).
Since then the limit changed to 3 total, however addressed

...indeed you are right about Octane users. There is a thread somewhere (on InsanelyMac, which is down right now) wherein a hackintosh user did some dabbling around and got 4x Nvidia working. I wonder if the same process can be applied to a cMP. I realise this is typical cMP talk of smacking square pegs into round holes, but so what.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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Flint Ironstag
(@flint-ironstag)
Estimable Member
Joined: 3 years ago
 

I think it's an interesting topic.  It's also telling that I can't email Apple, or any PCIe expansion chassis manufacturer, and get an answer to this question.  Pretty sure HP would tell me:

"we support x number of y cards in z box".  

Or support at Magma or CUBIX could tell me the same thing.  Found one of Tutor's threads.  It's not Mac specific, but there's a ton of good information, and I think there's discussion about cMPs.  Also try searching for cMP PCIe splitters / risers.  Some folks were looking into these for the mining craze.  Not sure how far they got.

https://render.otoy.com/forum/viewtopic.php?f=40&t=43597

[edit] old bare feats article: 5GPUs in cMP + CUBIX.

http://barefeats.com/gpu680v7.html

Just checked eBay - they sure want a lot of money for them!  But if you bought the whole shebang new in 2010 (!!!), it's presumably paid for itself many times over, and is still faster than TB3, so not too bad.  A while back @mcarver316 found them on sale at Amazon for $400, but I haven't seen them since.

[edit] also forgot about Cyclone - there's a seller on eBay that appears to be stripping their boxes down to the backplanes and selling the components.  If you have a cMP, this might be a cheapish way to load up.

https://www.ebay.com/itm/Cyclone-Microsystems-5-Slot-PCI-Express-Gen-2-x16-Expansion-System-Kit-Mac-PC/142698306871?hash=item21397b5d37:g:IGQAAOSweExaF1TA

MP 6,1 | 4c | d700
MP 6,1 | 6c | d500


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Aled Brown
(@gelert42)
Trusted Member
Joined: 3 years ago
 

It's like groundhog day this thread! I keep reading the same post over and over and over  Roll

2019 MBP15 2.4GHz i9 32GB with VEGA 20 dGPU - macOS 10.15
2019 LG 5K Mk2 94W Thunderbolt 3 Monitor (USB-C in)
Radeon Pro WX9100 16GB + Sonnet Breakaway 650W eGPU
Radeon RX 580 8GB + Sonnet Developer 350W eGPU


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highpass
(@highpass)
Eminent Member
Joined: 3 years ago
 

......Insanelymac is finally back up. Here is what one user altered to enable more than 3 GPUs. 

The user's post:  http://www.insanelymac.com/forum/topic/329008-3-gpus-work-4-gpus-fail-with-34couldn39t-allocate-runtime-area34/#entry2533997

The solution:  https://nickwoodhams.com/x99-hackintosh-osxaptiofixdrv-allocaterelocblock-error-update/

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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Chippy McChipset
(@chippy-mcchipset)
Reputable Member
Joined: 3 years ago
 

Would be curious if you could hook up 4 eGPU to the new iMac Pro. That is 4 ports on two controllers (each with a full set of PCIe lanes per TB3 spec) AFAIK, so in theory should be possible (once Apple offers official support).

Thunderbolt 3 Macs, Sonnet and OWC eGPUs, 4K Displays, etc


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Tutor
(@tutor)
New Member
Joined: 2 years ago
 

Whereas for a real MacPro 2009 to pre-cylinder/trashcan series (running pre-OS 10.8) max no. of Nvidia GPUs workable was 4 , now its 3.  Obviously, Apple OS has reduced GPU Input/Output (io) space.  I can, however, run additionally as a fourth GPU card an AMD 480.

To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.

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Chippy McChipset
(@chippy-mcchipset)
Reputable Member
Joined: 3 years ago
 

Upon further review I do think the practical answer to this question is "it depends on how many Thunderbolt 3 controllers your computer has." I don't think there's anything about 10.13.4 or later that prevents more than (for example) two eGPUs being used, but at the same time I don't know any Mac with more than two TB3 controllers. As soon as you connect two eGPU to ports on the same controller, each one is going to start cutting into the other one's performance most likely.

As a curiosity though I would like to see render benchmarks comparing two eGPU to four on Macs that don't have any inherent bandwidth limitations (a couple models have 20Gbps limitations on one of their TB3 ports).

Thunderbolt 3 Macs, Sonnet and OWC eGPUs, 4K Displays, etc


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Flint Ironstag
(@flint-ironstag)
Estimable Member
Joined: 3 years ago
 

Rominator / MVC has posted a MBP with 6 GPUs running (integrated, discrete, + 4 Titan Xp eGPU).

http://forum.netkas.org/index.php/topic,13703.0.html

MP 6,1 | 4c | d700
MP 6,1 | 6c | d500


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