I'm thinking of plugging in two GPUs in my simming rig... not SLI/Crossfire, just two GPUs. I currently have a 980Ti driving 5 monitors and I was just wondering if offloading the workload of two monitors would improve performance a bit. My three screens connect to the 980Ti via DP-to-DVI adapters, one touchscreen connects to the 980Ti via HDMI, and the other touchscreen connects via USB-to-DVI through a Targus docking station. I was thinking of adding a secondary card, whatever I can get for cheap (a 1GB GT 710 for £35 or a 2GB GT 710 for £40 sounds good), then connecting my two touchscreens to that GPU. My three big screens displays my sim, the two touchscreens only display Helios and Teamspeak.

Has anyone done something like this before?

I seem to recall back in the day people hooking up a 2nd monitor on a second card (because cards didn't support more than one monitor then) for the MFD in Falcon 4, but I never saw any concrete info about it beyond that it supposedly could be done.

My guess is that Windows can handle it fine but the individual applications need to be programmed for it, so YMMV depending on what you use.



The Jedi Master

It should work just fine for your additional touchscreens, if that's all you plan on doing with the second card.

Whether it'd actually improve performance noticeably is another question entirely, one that I don't know the answer to.

It may or it may not.... that's why I want to try it. Based on my FPS tests in BMS, it will give me at least a few FPS increases (3-5 average) but that's on a 5896x1080 resolution setup so that's not too bad...

What I wonder is if the cards I linked above can handle it. I think it should... but I could always be wrong. I think it should, after all, it's just two touchscreens with Helios and no graphically-intensive 3D stuff on it.

I managed to find a used GTX 660 Ti for cheap and have plugged it into my PC.... and immediately started running into issues.

1. My center touchscreen monitor would lose the "touch". Touching the center monitor and the PC thinks I'm touching my main display monitor. Going into Control Panel -> Tablet PC Settings -> Setup doesn't fix it because while I can skip the main monitors, when it asks me to "touch" the center touchscreen monitor, nothing happens on the touchscreen monitor and all the input registers on the main display monitor. Rebooting sometimes fixes the issues; otherwise, cold boot.

2. My center touchscreen monitor would lose the "touch" mid-flight.

3. Testing BMS, I have my own test routine and so far, I've tried it 3x and have not even managed to complete one run. My main screen or one of my touchscreens would go blue (is this the new Win10 BSOD?), there'd be a % counter, and the PC would reboot after that.

4. Booting up the PC, sometimes it would see both GPUs, sometimes it'll only see my 980 Ti and not the 660 Ti.

Managed to get a picture of the "blue screen" crash referred to in #3.




The funny thing was that this happened on my center touchscreen AFTER I managed one complete test in BMS. I was just on the BMS forums making a post when it happened. During the test, I did not even yet enter the 3D world when issue #2 happened and I lost touch control on the center touchscreen.

I wonder if the GTX 660 Ti I got is bad? But then again, why would I be having touchscreen issues? I'd see the point if I get display picture issues on the touchscreens as these are connected to the 660 Ti, but touch control AFAIK is transmitted via the USB cable.

FWIW, in the past when switching video cards I've needed to reinstall the drivers, even when the drivers ostensibly supported both cards.

Eg when going from a 570 to a 770, same drivers, but I needed to reinstall or I saw glitches, crashes, and other errors. So my process now is open new card, uninstall drivers on PC, shut down, swap cards, boot up, install same drivers again.

You didn't take out your old one, but you did add a new one.



The Jedi Master

Yeah, the 980 Ti is still powering the top three displays. The 660 Ti is just for the secondary touchscreens.

Opened up the PC again and repositioned the 660 Ti to the 8x slot. I initially had it on the lower, 4x slot to give my 980 Ti more breathing room but maybe that's the cause of the problems? So I now have it on the 8x slot and there's only a little space between it and the 980 Ti.... I guess it's good that the 980 Ti is bigger/wider so I can imagine it can still "breathe" even with the limited space due to the bigger fans and the slight overhang over the 660 Ti.

Well, the PC is more stable now. Not had a blue screen and managed to run several tests in BMS. I'm now more confused than ever.

The whole point of this exercise is to see whether it will improve performance and I was expecting a slight improvement or similar performance. What I got, however, was the opposite. I used to get 45-46fps average on my single GPU setup, with max fps at around 52-54. With my 2 GPUs, average is 41 fps and max dropped to 45-46 fps! I've even done a second round of testing and the numbers are consistent!

Why would I be getting worse performance? Why is a single-GPU setup giving better results than a 2-GPU setup?

Okay, done a few tests and trying to make sense of the results.

2 GPUs, 3 screens plugged into 980 Ti, no Helios, no YAME - min 44, max 56, avg 50
2 GPUs, 5 screens plugged in (3 to 980 Ti, 2 to 660 Ti), no Helios, no YAME - min 44, max 56, avg 50
2 GPUs, 5 screens plugged in (3 to 980 Ti, 1 to Targus, 1 to motherboard), no Helios, no YAME - min 45, max 56, avg 50
From these tests, we can see that the addition of the two touchscreens does not really affect the FPS numbers regardless of where the touchscreens are plugged in. During testing, the touchscreens simply showed my desktop wallpaper, so there was minimal load.

2 GPUs, 5 screens plugged in (3 to 980 Ti, 2 to 660 Ti), Helios, YAME - min 36, max 45, avg 41
2 GPUs, 5 screens plugged in (3 to 980 Ti, 1 to Targus, 1 to motherboard), Helios, YAME - min 38, max 47, avg 42
Again, we can see that with the added load of Helios and YAME, the performance is the same regardless of where the touchscreens are plugged in. There is an average drop of 8fps though, due to the additional workload.

1 GPU (980 Ti only), 5 screens plugged in (3 to 980 Ti, 1 to Targus, 1 to motherboard), Helios, YAME - min 40, max 50, avg 45
This is where things get blown out of the water. Minimum FPS is higher, max FPS is higher, average FPS is higher. Sure, there's still a drop in performance due to the added load of Helios and YAME, but **REMOVING** the 660 Ti improves performance? What?!?!??


Here's a graph of the average FPS numbers over the tests:


On the first graph, the green line was when the touchscreens were plugged in via Targus and direct to the motherboard. It's interesting to note that the green line is most of the time mid-way between the blue and red lines.

On the second graph, the green line is for the test with the 980 Ti only. It is blatantly obvious that the two-GPU setup was nowhere near the single-GPU performance numbers! Also note that the FPS numbers were WORSE when the touchscreens were plugged into the 660 Ti (blue line)!!

Why was the 980 Ti hampered by the presence of the 660 Ti?
Why were the framerates better when the touchscreens were plugged into the USB/motherboard compared to when they were plugged into the 660 Ti?

While this puts the final nail in the coffin regarding the decision to use one or two GPUs, I cannot help but wonder why the 980 Ti was hampered by the presence of the 660 Ti. Remember that on both with and without Helios/YAME tests, I've tested with the screens plugged into the 660 Ti and with the screens plugged into USB (Targus) and motherboard but it was only when I removed the 660 Ti from the PC itself that the FPS numbers went up by a good bit.

Are the PCI lanes limited on your motherboard specifically when a 2nd GPU is added?

How can I determine that? The motherboard is a Z170X Gaming 7 board by Gigabyte so I wouldn't have though there would be a limit to the second lane...

Someone suggested that it might be PhysX that is interfering with my FPS numbers so ran a few tests with PhysX set to the 980 Ti, then to the 660 Ti, then to the 660 Ti with the Dedicated box ticked. With the monitors on the 980 Ti + Targus + Motherboard configuration, it was interesting to see that the 660 Ti seemed to not run at all according to HWiNFO records. When the two touchscreens were plugged into the 660 Ti, it's usage increased to a max of 20%. However, on all tests with the 660 Ti plugged in, my frames were at 41-42fps average.

Unplugged the 660 Ti and naturally, PhysX was set to run on the only card available, the 980 Ti. Monitors were plugged on the 980 Ti + Targus + Motherboard configuration and frames were at 45-46fps average.

I think this also shows that when the usage of the 660 Ti was zero (0% on Core Load max) and I was still getting 41-42fps average, this means that the PCI lane to the 660 Ti is not being used at all but I still get the framerate drop.

Bought a new cable for my monitor so now my setup is as follows:
3 primary displays connects to the 980 Ti via DVI-to-DP adapter cable
1 touchscreen (L) connects to the motherboard via DVI-to-DP adapter cable
1 touchscreen (R) connects to the motherboard via HDMI cable

Windows sees all screens and the two touchscreens are controlled via the motherboards Intel GPU. The weird thing is that when I turn off the left touchscreen (DVI-to-DP), it "disappears" from Windows entirely, as if it's not connected at all. If I turn off the right touchscreen, it's still there and Windows still sees it, unaware that it's just powered off. Ironically, the left touchscreen is the "primary display" as far as the Intel GPU is concerned.

When properly configured, my setup looks like this under Windows Display Settings


[2] is my nVidia Surround screens, [3] is the L touchscreen, and [1] is the R touchscreen. When I turn off [3], it disappears from this screen altogether and I'm just left with [1][2]. What makes it even weirder is that sometimes, when I boot up the computer, it won't see [1] at all.... but then I turn on the L touchscreen and Windows sees that. I leave the L touchscreen on, boot up a couple more times, and sometimes it'll see the R touchscreen and my setup is okay, most of the time it'll only see the L touchscreen and I'll have to add the R touchscreen via the Intel GPU control page.