Poor GPU performance when enter Play In Editor (PIE) mode

Development Platform & Builds Debugging, Optimization, & Profiling
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Hi all !
I’ve a GPU performance problem on my project and don’t found the cause.

There is the facts: When I am on Editor (or Simulate In Editor) mode, the framerate of my scene is at 60FPS (16ms of GPU Time) on my 4K screen. But when I go into Play in Editor mode, the GPU time go to 28ms (38 FPS) and I don’t found any reason for this for now, I don’t know where to search !

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I tryed:

  • Not possess my pawn
  • Hide my Landscape
  • Hide my pawn (the Grizzly)

Nothing of this make my GPU Time same between SIE and PIE mode, the render quality appear to be the same !

On the GPU debug stat, I see this differences :

GPU Passes (inclusive) SIE PIE ×
Lumen ScreenProbeGather ≈ 2.1 ms ≈ 5.8 ms 2.8×
DiffuseIndirect + AO ≈ 2.7 ms ≈ 6.9 ms 2.5×
Nanite VisBuffer ≈ 2.2 ms ≈ 4.2 ms 1.9×
ShadowDepths (VSM) ≈ 2.8 ms ≈ 4.7 ms 1.7×
Hair Strands (groom) ≈ 1 ms ≈ 3.3 ms 3.3×

(for the difference about the Groom rendering time, it’s caused by of the difference of FOV between editor and play mode (shorter FOV in PIE, more close to Groom asset) )

I tryed to compare scalability settings or screen percentage on both mode, with the command:
r.ScreenPercentage
all are the same (Epic preset and 100% screen percentage)

output of the command in SIE:
Cmd: r.ScreenPercentage
HISTORY Constructor: 0.000000
Scalability: 100.000000
r.ScreenPercentage = "100"
LastSetBy: Scalability

output of the command in PIE:
Cmd: r.ScreenPercentage
HISTORY Constructor: 0.000000
Scalability: 100.000000
r.ScreenPercentage = "100"
LastSetBy: Scalability

I tryed to make a “diff” between the output of the command DumpCVars in PIE and SIE mode, and the output are identiqual …

don’t know what to tryed now or where to search…

If someone have an Idea of what to do …
thanks you a lot !

2

Hi, did you try to print the actual render/viewport resolution? (There was a blueprint node for that, not at my PC right now). Cause when playing inside the editor it usually has a lower rendering resolution on my end (full HD on a 4k monitor). If playing inside a new editor window renders at 4k and in editor at full HD that would explain the difference in performance. Also in editor it’s usually not rendering the whole screen area, further reducing the actual render resolution.

Also I would recommend to test performance in a shipped build, or at least in standalone, not running in the editor as that will give you (arbitrary) wrong results.

3

Okay. I don’t know why, but the editor viewport resolution scale often go back to a default value that don’t render 100% and my BP override the renderscale to set it at 100% at runtime before apply DLSS.
I’m really confused why we didn’t see this early because this problems is not new…
So, that’s why we have a big Frame time difference.

We will have to work harder to optimise our landscape to reduce de GPU costs. Lumen is really hard to master for containing per frame costs. We hesitate to going back to standard light Pipeline.