Configuring multiple GPU for Resolve Studio

Hi folks, I am using Resolve Studio 12.5.5 and my PC has 2 AMD Radeon R9 390 series GPUs. Because I have 2 GPUs, I can set it up in AMD CrossFireX configuration. However, when I enable AMD CRossFireX, Resolve only display 1 video card (see Figure 2 in the attached picture) on its System Preference display. If I disable the AMD CrossFireX, it then shows I have two video cards (see Figure 1 in the attached picture). What does this mean and how does this work in Resolve? Does Resolve uses the CrossFireX and treat it as one video card with multiple GPU and combine the total VRAMs to boost performance? Or is it better to disable CrossFireX and will Resolve use both cards independently? If anyone has good experience with this, can you please help demystify and show which is the appropriate way to configure and get both cards so that it is best utilize by Resolve (with or without CrossFireX enabled)? Thanks!

GPU and DaVinci Resolve.jpg (227.37 KiB) Viewed 6654 times

There's over 70 views in the last hour but 0 response. Is this something that no one encountered or unusual setup?

[Peter Chamberlain]

We don't use or need Crossfire to get maximum performance from multiple GPUs. Same for SLI with NVIDIA, just leave them off.

Got it. I also checked the "Use Display GPU as compute". Will this make it perform much better? How do I know which GPU card has what load? Both cards has 8Gb of VRAM. Will Resolve use both cards VRAM?

No one answered in the 1st place because this is a well known case of RTFM... and there are a looooot of threads about Resolve not using any SLI or Crossfire here on the forum as well

However, about your second question (very very discussed too here around) : keep "Use Display GPU as compute" ticked, this will have the GUI card help the computing one if needed.
The GUI card is the one hooked up to the monitor...
It can use 8 Go vram in your case (if your cards had different vram, you may want to leave it unticked, because the maximum vram limit would be the "max of the weakest card")

And for the pre allocated system memory: advises to leave to 4000 (Unless you know what you're doing).

Okay Sam... Both cards have 8gb VRAM.
Jean, the 12000 is the default value for the prealloc system memory when Resolve was installed. I have not made any changes to it. Why change it to 4000?

EDIT: I did some research on the prealloc system memory and depending on how much RAM there is Resolve sets the prealloc accordingly. The more memory you have the bigger the allocation. In my case I have > 32gb of RAM so it set it to 12000.

viewtopic.php?f=21&t=56896&p=326554&hilit=system+memory#p326371
viewtopic.php?f=21&t=56896&p=326554&hilit=system+memory#p326554

Because the manual says (page 97): the default is 4GB and if you have 64 to 128 GB RAM you can increase it. Only affects images. At me also the default is 4GB(and i have 32GB RAM on my PC). Surprised whether it's 12GB on your computer?

Alright Jean. I'll change it to 4 and give it a shot. I read the manual but nothing really indicates how to correctly calculate it and with Resolve setting it at 12 on my PC without me changing it, I wonder how it came to that number. Still a mystery for me. Thanks!