iMac Pro + eGPU advice needed

Hi there!

I´m on an iMac Pro (18 Core, 64 GB, VEGA 64) with an external attached NVIDIA TITAN Xp with 12GB VRAM (via Thunderbolt3 / Sonnet eGFX-Box).
With help from the awesome guys of egpu.io i managed to get this setup running under mac OS 10.13.4 and showing up for use in Resolve.

That´s the good news...
Bad news:
Performance within Resolve 15b isn´t blowing me away. In fact it isn´t much of a difference between using the internal VEGA64 only (Open CL), TITAN Xp only (CUDA) and using both GPUs together (Open CL).
Using the GPU-History-Panel within Activity-Monitor i can see that the GPUs are used heavily during playback according to the chosen settings in Resolve - so generally it works.
Playback (R3D-Raw 5K with medium compression is smooth in either configuration) BUT using OFX such as BorisFX or even some Resolve internal FX will slow-down playback a lot.
My good old MacPro (Trashcan, 12-Core, D700) nearly shows the same performance in this project.

I hoped to gain more realtime-performance with the new iMac Pro + eGPU.

Now the question:
I know it´s not the perfect solution to mix two different GPUs (AMD internal + NVIDIA external).
Does it make sense to swap the TITAN Xp against an AMD VEGA 64 Frontier performance-wise?
Or any other hardware-suggestions (no, i don´t wanna switch to Win/Linux) ?

THANKS in advance,

Daniel

You need to find out if OFX plugins will use more than 1 GPU in Resolve. This is not so obvious at all and will most likely also depend on the plugin itself.
Try first Resolve own processing, RED debayering etc. Also mixing GPU types may be bad idea. Another thing is that 1 GPU is internal and 2nd external which means a lot of data copying- in this case TB3 is actually quite slow.
I think external GPU is good when internal GPU is slow and then you switch to external. In this case your mix maybe be nothing good at all and pure waste fo money.

+ most OFX if they are not optmised for GPU use one thread of one core only.... it's kinda sad to see 47 threads sitting, and one running at 40%
<sigh>
and turn on node cache

thanks for your input, guys.

Of course i tried different settings (GPU debayering on/off, Use Display GPU for processing on/off,etc.) and i can confirm that using the GPU für RED Debayering speeds up playback a lot.
Maybe this is the point and i´m expecting too much:
When GPUs are processing the RAW debayering + grading there´s maybe not much "juice" left for an OFX Transition.
In case of a transition we are talking of this realtime-action:
Debayering two 5K-RAW-Video-Streams, processing 2 x grading-trees with some nodes AND on top of that computing the OFX-Transition...


Anyway i´m going to try swapping the TITAN against an AMD-GPU and see if this will help gaining performance.
Also i´m going to talk to BorisFX if there´s something i can do to optimise playback or if there are some optimisations from their side in the pipeline...
We´ll see...

it is not a good idea mixing two different brands gpus.