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Odd interaction between eGPU and Thunderbolt monitor, disabling external GPU  

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LackingUtility
(@lackingutility)
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Joined: 1 year ago
Posts: 10
December 19, 2018 5:31 am  

I've got a Mid 2015 Macbook Pro with an internal AMD Radeon R9, and I hooked it up to a Sonnet eGFX with an NVidia GTX 1060, and everything's been working beautifully. I was running 3 external monitors off the 1060, plus the laptop's internal, and everyone was totally happy.

But then I decided to hook up my Thunderbolt Display, too. Why, if 4 monitors are good, 5 monitors are better! Suddenly, performance was crawling. I looked in the About screen, and low and behold, the Radeon R9 was trying to run all 5 monitors, and the GTX 1060 wasn't even showing up. Unplug the Thunderbolt Display, reload the About screen, and there's the GTX running 4 monitors again. Doesn't even need a reboot - plug in Thunderbolt Display, all 5 on the Radeon; unplug it, all (remaining) 4 on the GTX.
Screenshots attached.

Anyone have any ideas?
Running High Sierra 10.13.3, and NVidia Web Driver 387.10.10.10.25.156

Screen Shot 2018 12 19 at 12.21.14 AM
Screen Shot 2018 12 19 at 12.21.26 AM
Screen Shot 2018 12 19 at 12.22.39 AM
Screen Shot 2018 12 19 at 12.22.32 AM
Screen Shot 2018 12 19 at 12.23.41 AM

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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LackingUtility
(@lackingutility)
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Joined: 1 year ago
Posts: 10
December 19, 2018 5:35 am  

Additional bit of info... If I close the lid on the MBP, then the GTX powers the three monitors it's connected to and the Radeon powers the Thunderbolt. Much improved (but at the loss of the internal monitor).

Screen Shot 2018 12 19 at 12.35.11 AM

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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theitsage
(@itsage)
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Posts: 3939
December 21, 2018 5:48 pm  

"About this Mac" doesn't always show the correct information as far as which GPU powers which display. Can you open up System Information and go the Graphics/Displays tree to take screen caps? The Radeon R9 M370x dGPU should power the internal display and Thunderbolt Display while the GTX 1060 eGPU should power all monitors directly connected to its ports. The sluggish behavior you observed when the Thunderbolt monitor was connected might be due to shared bandwidth on a single Thunderbolt 2 controller. Download and run CL!ng to check with and without Thunderbolt Display connected.

Best ultrabooks for eGPU use

eGPU enclosure buying guide

94 external GPU build guides


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LackingUtility
(@lackingutility)
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Joined: 1 year ago
Posts: 10
December 23, 2018 9:51 pm  

"About this Mac" doesn't always show the correct information as far as which GPU powers which display. Can you open up System Information and go the Graphics/Displays tree to take screen caps? The Radeon R9 M370x dGPU should power the internal display and Thunderbolt Display while the GTX 1060 eGPU should power all monitors directly connected to its ports.

You're exactly right... Display info is incorrect, but the System Info>Graphics/Displays tree properly lists the internal and TB Display off the R9, and the three externals off the GTX. Thanks!

The sluggish behavior you observed when the Thunderbolt monitor was connected might be due to shared bandwidth on a single Thunderbolt 2 controller. Download and run CL!ng to check with and without Thunderbolt Display connected.

That looks like it, too... Device to Device transfer drops by about 5GB/s when the TB Display is connected.

Welp, good to know it's just a bus limitation that I can address with my next upgrade, and not a bug.

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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theitsage
(@itsage)
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December 23, 2018 11:30 pm  

@lackingutility Thank you for the update of your findings. Glad you got to the bottom of it.

Best ultrabooks for eGPU use

eGPU enclosure buying guide

94 external GPU build guides


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joevt
(@joevt)
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Posts: 341
December 24, 2018 1:06 am  

What does "Device to Device transfer drops by about 5GB/s" mean?

Pending: Add my system information and expected eGPU configuration to my signature to give context to my posts


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