Rendering framedrops on overlapping shadows since 2.8

[Noctrach]

  Not VR, but I'm seeing very curious behaviour on the rendering of overlapping shadows specifically.

This can be either:

• Object Shadows drawn on Terrain Object Shadows (disabling either will fix)
• Closely packed objects with their own shading (tightly packed groups of trees, even with all shadows turned off)

Maybe it can help trace down other performance issues in general. With object shadows enabled the game's render thread exhibits this kind of strange "frameskipping" at regular intervals:

Fullscreen mode:

So for testing, I added the script suggested by @BIGNEWY here

Behold, Borderless Windowed after using alt+enter - The framedrops are gone! (So is my framerate, but its at least stable)

Note that the spikes at the end are the screenshot event in both pictures. The stall happens exclusively in rendering. Both pictures are taken with sim paused, hence the CPU frametime of 0.15 ms until moment of screenshot.

Note how these spikes also disappear entirely when EITHER Shadows or Terrain Object Shadows are set to OFF
Flat Shadows still have the same impact when rendered in Fullscreen Exclusive
Large groups of trees may also still cause identical framespike patterns

These spikes also disappear if NO entities casting Terrain Object Shadows are present in FOV

(e.g. If you look down at an Apache and no trees are in frame --> No dropped frames)

These spikes however do happen if BOTH Shadows and Terrain Object Shadows are off, but tightly packed trees are nearby and inside FOV

My graphics settings:

  

My system: 5800X3D CPU, 32GB RAM, 6600 XT GPU

Edited November 16, 2022 by Noctrach

[Noctrach]

Addendum:

There's definitely a factor of the object/LOD mix that is together on-screen. E.g. removing either nearby trees or distant objects from the camera FOV will also completely eliminate the framedrops.

All shadows AND terrain object shadows turned off
Game in fullscreen (script removed)

 

Edited November 16, 2022 by Noctrach