Reduce CPU usage when Distant Horizons is present

[Excederus]

Is your feature request related to a problem? Please describe.
Using C2ME and DH together in more modded scenarios without changing any config causes massive lagspikes during vanilla chunk generation even on lower/reasonable view distances like 12. This is most likely caused by CPU usage, since my CPU is pinned to 100% all the time when generating chunks no matter DHs CPU Load setting. Reducing DHs CPU Load to Minimal Impact eliminates the FPS drops during initial generation but still causes minor to medium stutters while moving. Using ZGC also only helped a bit.

Describe the solution you'd like
When C2ME detects that DH is installed reduce the amount of CPU resources allocated to C2ME/chunk generation to prevent the CPU from getting pinned to 100% and causing FPS Drops/Stutters

Describe alternatives you've considered
Right now I don't think there really is an alternative to just removing either C2ME or DH

Additional context
Ryzen 5 7600X - 32GB 6000MHz RAM (8GB allocated to MC) - RTX 2070 - NVME
Currently testing with 65 mods (excluding libraries) however I observed that the performance issues get worse with each mod added. I previously had an instance with around 150 mods where simply walking in one direction caused FPS drops/Stutters to 10fps.

Some tests I did:
Any combination other than C2ME + DH: 130fps - 110fps (gradually decreasing with visible chunks)
C2ME + DH: 20fps during generation - jumps to 110fps when vanilla generation is done

Tests done at 32 view distance, 32 simulation distance, 256 LOD distance, Balanced DH CPU Load, Bliss Shaders

[ishland]

Try changing generator mode from Features to Internal Server

[Excederus]

Same settings as the other tests (except changing generator mode):
20-30fps during initial generation - 110fps when done and standing still - 15-20fps while moving - constant 100% CPU usage
Changing to view distance 12:
50-70fps with medium stutters while moving - constant 100% CPU usage
Additionally changing DH CPU Load to Minimal Impact:
110fps with very very rare micro stutter - 70-90% CPU usage

Basically not changing much, if any a minor improvement

[Excederus]

Recommendation from the DH discord to lower the "globalExecutorParallelism" from default (6) to 4 significantly reduced the stutters and increased average FPS during generation to ~45fps, while keeping 32 view distance and Balanced CPU Load in DH.

For anyone who comes here looking to fix FPS when using both mods:
C2ME seems to calculate your amount of CPU (v)-cores and then defaults to using half of them. So if you have a 2 core 4 thread CPU then setting it to 4 (like I did for my CPU) would use all your cores for C2ME and probably be even laggier than before. So check the number after Default in the comment above the variable and use half of that.
For example with a 4 core 8 thread CPU the comment most likely says "(Default: 4)" then set the variable to 2.

[mpustovoi]

Does config changing work in runtime?
I set the globalExecutorParallelism from 4 to "default" value while being in game and the FPS drops seem to have stopped, but the chunks started loading slower, or it's just a coincidence.

# (Default: 1) Configures the parallelism of global executor
globalExecutorParallelism = "default"

[ishland]

Does config changing work in runtime?

No. Config is only read and updated once on game startup.