Question Dual display with mixed graphics cards?

Feb 22, 2020
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Greetings, I have a bit of a conundrum. I have a Radeon VII and a GTX 1080 Ti in my system and am running dual displays. For some reason both displays only work when connected to different cards. Any suggestions or ideas on why this is happening?
 

Wolfshadw

Titan
Moderator
Should not be an issue connecting both displays to a single card. I'd remove one card and reconnect both displays to the other card and try and discover why it's not working.

Are you getting no display on the second monitor or the same screen?

-Wolf sends
 
Feb 22, 2020
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Each card individually powers both displays. When both monitors are connected to the radeon 7 the primary monitor doesn't display and while trying to auto detect the secondary monitor loses image intermittently, consistent behavior with the primary monitor changing resolutions or tabbing in/out of a fullscreen program. *when both cards are installed * sorry for not clarifying that in my initial response.
 

Wolfshadw

Titan
Moderator
1) Please list the relevant components:
a. Model number of the Primary Display
b. Model number of the Secondary Display
c. Model number of the GTX 1080 Ti
d. Model number of the Radeon VII
e. Model number of the Power Supply
f. Model number of the Motherboard.

  1. Pick one card and install it into the top PCI-Ex16 expansion slot. Leave the other card uninstalled outside of the system.
  2. Make sure you have the necessary power connectors from the power supply to the graphics card.
  3. Connect both displays to the graphics card outputs.
  4. Boot up your system and tell us what you see.
-Wolf sends
 
Feb 22, 2020
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Both displays are Asus vg248 monitors using display port.
TURBO-GTX1080TI-11G for the Asus 1080.
RX-VEGMA3FD6 for the radeon 7.
220-T2-0850-X1 for the EVGA supernova PSU.
Motherboard is Asus x99-deluxe II.

Both cards were fully tested and gamed on individually by me for several months using all of the same components before I attempted to run both cards in the system and each performed as I expected. Only when running both cards and both displays connected to the radeon 7 has there been an issue. I have NOT tried connecting both displays to the 1080 while both cards are installed. System seems stable with displays on separate cards.
 
Feb 22, 2020
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i7-6900K, radeon in top slot and 1080 in bottom most slot. If I remember correctly that is the recommended configuration for my motherboard to have both cards functioning at 16x lanes.
 

Wolfshadw

Titan
Moderator
The Intel Core I7-6900K processor has a max # of PCI Express lanes of 40, so you should use the configuration as described in your manual.

Motherboard Manual Pg 1-8


The second card should be in PCIEX16_3 to allow for the full X16 throughput.

-Wolf sends
 
Feb 22, 2020
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That doesn't address the problem though as the known 16x card having both displays connected to it did not result in both displays working correctly. Not sure why slot 3 is the recommended slot when it's also shared with the m.2 port.
 

Wolfshadw

Titan
Moderator
Ok, so with only the Radeon VII installed in PCIEX16_1 (the GTX 1080Ti is NOT in the system at all), and both displays are connected to it, you get dual-display working.
With only the GTX 1080Ti installed in PCIEX16_1 (the Radeon VII is NOT in the system at all) and both displays are connected to it, you get dual-display working.
With Both cards installed; the Radeon VII installed in PCIEX16_1 and the GTX 1080Ti installed in PCIEX16_5 and one display connected to each card, you get dual-display working.

It's only with both cards installed; the Radeon VII installed in PCIEX16_1 and the GTX 1080Ti installed in PCIEX16_5 and both displays connected to the Radeon VII that you're having issues with dual-displays.

Is the above assessment correct?

-Wolf sends

Edit:

Not sure why slot 3 is the recommended slot when it's also shared with the m.2 port.
It's a trade off. You can use one feature or the other. You cannot use both.
 
Feb 22, 2020
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I didn't move the card because I haven't had time to get to my computer, it will have to wait until tomorrow.
To be honest, I wasn't expecting this experiment to do anything amazing. The goal was to see if I could use the nvidia card for extra processing power as if it were a Tesla card, not as an extra display adapter. The radeon vii doesn't even support crossfire so there's no reason to get a second one even if I can get these two cards behaving together and get a minor system performance boost.
If moving the 1080 doesn't help and no solution for getting both displays on the radeon is found then I'll likely pull the 1080 and shelve it as an emergency backup.
 

Wolfshadw

Titan
Moderator
Even if you could get both displays running off of the Radeon VII with the GTX 1080Ti installed, you would not get any performance improvement from it. Only if you added another display (or three) would it be of any use.

-Wolf sends
 
Feb 22, 2020
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Okay, testing that I've done this morning. Both displays plugged into 1080 resulted in no working displays. Moved 1080 up to slot 3 and behavior did not change.

Removing 1080 now as a semi failed experiment despite marginal processing improvement since I cannot find a way to use only the radeon 7 for graphics with both cards in.
 

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