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eGPU benefit on internal monitor?


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#1 jgwdoc

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Posted 16 July 2018 - 07:44 PM

I'm a little confused by the various Apple support documents on the new Blackmagic eGPU. It seems like it only provides acceleration for applications run on an external monitor?
Is there any benefit if you're trying to run an application (game) on the internal monitor of a MBP?  Is there a way to tell the MBP to use the external GPU for all functions?
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#2 Cougar

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Posted 16 July 2018 - 08:46 PM

Only internal GPUs can power internal monitors. There's kind of sort of a way around this, but it requires developers to add support for it and it would hurt performance. See "Internal Display" here: https://9to5mac.com/...-of-egpu-video/

#3 jgwdoc

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Posted 16 July 2018 - 09:41 PM

Thanks. That was my impression, but some of the commentary on the Apple support site is confusing. It seems like there are a few hacks that might essentially fool the machine into thinking the internal monitor is actually external, but probably not worth the trouble and might crash with each OS update.
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#4 Sneaky Snake

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Posted 17 July 2018 - 03:55 PM

Even if it works your performance is significantly worse compared to an external monitor. The reason being that the TB cable has limited bandwidth and if you have to pipe all of the display data back over the TB cable to your internal screen it uses up some of that precious bandwidth.

Internal Display data path: Computer -> TB cable -> eGPU -> TB cable -> Internal Display
External Display data path: Computer -> TB cable -> eGPU -> HDMI/DP -> External Display

Various benchmarks of eGPU's on Youtube (Razer Core for example) showcase this performance loss.
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#5 jgwdoc

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Posted 18 July 2018 - 09:55 PM

The thing I find confusing is whether applications run on the internal screen of the MBP are themselves able to use the external GPU, regardless of whether the internal screen is accelerated or not? Perhaps my question just reflects my ignorance, but is the eGPU only able to accelerate applications that output through an external screen?
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