Partially working Optimus in Win 10 Bootcamp (I think)

[Alarming0]

Hey everyone, so I've been trying to get my eGPU working on my girlfriend's iMac. An external monitor is working thus far, but of course I have run into the standard issues that people have while trying to run on the internal LCD on Macs with dGPUs (in my case a GT 750m). I used to run this eGPU on an Asus laptop (with Windows 7) via mPCIe and really wanted to use the internal screen in that case as well. One thing that DID NOT work for my previous laptop/eGPU was starting a game on the external monitor, setting it to windowed mode, and then moving the window onto the internal screen. On my laptop, doing this with e.g. afterburner open would let you watch the dGPU (GTX 560m) switch the load back and forth with the eGPU (GTX 950) (or split the load when you dragged the window onto both monitors). On the iMac in Win 10 Bootcamp this is not how it works, *switching the window between internal and external LCD continues to use the eGPU to render the game*, presumably engaging Optimus on some level and ultimately *just working*. I have confirmed the load on the eGPU to properly correspond to the expected load in the game as well as the GPU indicator task bar icon indicating that the eGPU is rendering the game.

 

The issue however is that when you do this the GPU takes a massive performance hit. I cannot tell if this is just the effect of Optimus (because I can't run Optimus benchmarks like firestrike because that would require me to switch the monitor which I don't think is possible) or if there is more to this performance hit. We're talking basically a straight 50% of the framerate in multiple games despite the same load. Is this expected Optimus performance? I only have a GTX 950 so I don't know if perhaps people with stronger GPUs might see better performance in this case. Alternatively, I was thinking that because I am unable to install Intel Graphics Drivers there may be some functionality that is lost. Sorry if this has been discussed, I looked everywhere for other threads like this one without luck.

 

EDIT: Ok after much testing I can safely say the following: The eGPU definitely continues to render the game and then transfers that to the iMac's internal screen. Doing this causes both the dGPU and CPU to throttle resulting in mostly unplayable experiences. If I can somehow stop this throttling I think this will result in functional eGPU on internal screen.

Edited May 14, 2016 by Alarming0

[Alarming0]

Update: Overclocking the iMac monitor shows that the framerate is being capped at 50% of the refresh rate most of the time. If only I could OC to 120hz lol

[Alarming0]

Just going to keep speculating: Looks like the dGPU is being used to display the output from the eGPU because it shows a constant ~30% load. I'm guessing that using the eGPU being in use throttles the dGPU, perhaps allowing it to use more load is the solution here.

Edited May 14, 2016 by Alarming0