Adding 2 Rendering Windows doesn't effect main thread but a 3rd kills it

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Are you using Developer Mode or made changes in it?

Yes, on for monitoring.

Have you disabled/removed all your mods and addons?

Yes - no difference

Brief description of the issue:

Using the EXERMENTAL multi monitor setup, if I add an additional 1 display (to create a total of 2) then I get near zero FPS hit. My main thread time goes from 11ms with 1 display to around 12ms with 2 displays. If I add a third (as you do with a proper triple monitor setup then FPS is reduced by approx. 50% with my main thread time going from 12ms to 30ms. This drop occurs only when adding the third window, not the second and occurs regardless of the rendering size of the windows (i.e 4k or 2k). I

It doesn’t matter where the 3rd window is positioned or adjusted to - adding the third halves the main thread time.

Provide Screenshot(s)/video(s) of the issue encountered:

Can if required

Detailed steps to reproduce the issue encountered:

Simply add an additional rendering window and then add a third.

Many issues may be due to an outdated graphics card. Please state your Graphics Card Driver Manufacturer (NVIDIA, Intel, AMD) and Version (Learn how to find your current graphics card driver version):

7900X3D, CL30 6000Mhz RAM, 4090.

PC specs and/or peripheral set up if relevant:

3 x 4k 55" TVs. It doesn’t matter which display is displaying which window - its always adding a 3rd that kills main thread time.

Build Version # when you first started experiencing this issue:

All builds

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Do you have the same issue if you follow the OP’s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

Do you have FrameGeneration on? Without it I have quite pleasant triple screen experience.
When FG is ON everything is ok only up to 2 windows like you described. 7800x3d 4090.

with FG ON

with FG OFF

Thats interesting. I do run with FG on, although note it only works on the main screen not the two side monitors anyway.

I wonder why putting FG on would increase the main thread time? I thought that was purely GPU driven…

With 3 screens with FG ON the main screen is driving others - if you have 40 raw fps ( smooth 80 with FG ) on the main window then other windows have to have choppy 40fps and mainthread goes high because of waiting doing nothing despite you have resources to generate more frames - there is no cpu bottleneck. That’s why I fly without FG and get 50-60 fps on all windows.

this is exaple when fps is artificialy limited, main thread goes high but cpu is almost idle