Tested with only ImmediatelyFast installed, using Fabric.

Screenshots:

Log: https://mclo.gs/PDdwRAE
Log spam is because of Hypixel.

@mrjasonn I think I found a fix. I can't test it tho due to not owning a mac. Can you test it: https://upload.raphimc.net/u/XI8WKg.jar

And also upload screenshots of F3 with and without the fix (fix_slow_buffer_upload_on_apple_gpu in the config file) to confirm that the fix is still improving performance (Hypixel lobby or any scene where there is more than just an empty world is a good place to test it)

Could not reproduce this:

This might be a MacOS exclusive bug. Do you have any other computer where you could test the same ImmediatelyFast version.
Also try setting debug_only_and_not_recommended_disable_universal_batching to true for testing (Make sure to set it to false again after testing because that option essentially disables large parts of the mod)

Can you test if your issue also exists in 1.21.5 with only ImmediatelyFast or if it is only 1.21.6

Could not reproduce this:

This might be a MacOS exclusive bug. Do you have any other computer where you could test the same ImmediatelyFast version. Also try setting debug_only_and_not_recommended_disable_universal_batching to true for testing (Make sure to set it to false again after testing because that option essentially disables large parts of the mod)

Yep, still happening with that config set. Tested on the same machine.
New log in case it is useful: https://mclo.gs/fLW5HRy

Try replacing your config with this one (Its everything disabled) and check again:

{
  "REGULAR_INFO": "----- Regular config values below -----",
  "font_atlas_resizing": false,
  "map_atlas_generation": false,
  "fast_text_lookup": false,
  "avoid_redundant_framebuffer_switching": false,
  "fix_slow_buffer_upload_on_apple_gpu": false,
  "COSMETIC_INFO": "----- Cosmetic only config values below (Does not optimize anything) -----",
  "dont_add_info_into_debug_hud": false,
  "EXPERIMENTAL_INFO": "----- Experimental config values below (Rendering glitches may occur) -----",
  "experimental_disable_error_checking": false,
  "experimental_disable_resource_pack_conflict_handling": false,
  "experimental_sign_text_buffering": false,
  "DEBUG_INFO": "----- Debug only config values below (Do not touch) -----",
  "debug_only_and_not_recommended_disable_universal_batching": true,
  "debug_only_and_not_recommended_disable_mod_conflict_handling": false,
  "debug_only_and_not_recommended_disable_hardware_conflict_handling": false,
  "debug_only_print_additional_error_information": false,
  "debug_only_use_last_usage_for_batch_ordering": false
}

If that fixes the issue, try reenabling settings one by one until you find out which setting exactly breaks it

Try replacing your config with this one (Its everything disabled) and check again:

{
  "REGULAR_INFO": "----- Regular config values below -----",
  "font_atlas_resizing": false,
  "map_atlas_generation": false,
  "fast_text_lookup": false,
  "avoid_redundant_framebuffer_switching": false,
  "fix_slow_buffer_upload_on_apple_gpu": false,
  "COSMETIC_INFO": "----- Cosmetic only config values below (Does not optimize anything) -----",
  "dont_add_info_into_debug_hud": false,
  "EXPERIMENTAL_INFO": "----- Experimental config values below (Rendering glitches may occur) -----",
  "experimental_disable_error_checking": false,
  "experimental_disable_resource_pack_conflict_handling": false,
  "experimental_sign_text_buffering": false,
  "DEBUG_INFO": "----- Debug only config values below (Do not touch) -----",
  "debug_only_and_not_recommended_disable_universal_batching": true,
  "debug_only_and_not_recommended_disable_mod_conflict_handling": false,
  "debug_only_and_not_recommended_disable_hardware_conflict_handling": false,
  "debug_only_print_additional_error_information": false,
  "debug_only_use_last_usage_for_batch_ordering": false
}

If that fixes the issue, try reenabling settings one by one until you find out which setting exactly breaks it

I have tested, and the slow buffer fix on Apple GPUs had caused the issue. Please fix it, but not remove it, as it really helps with lag.

Can you test if your issue also exists in 1.21.5 with only ImmediatelyFast or if it is only 1.21.6

It does not exist in 1.21.5.

@RaphiMC, potentially you could take a look at 1.21.6's code and you might find something out that may help fix the issue.

I am having this problem as well on macOS with my M4 pro. I have subscribed to this issue, but is there anything I can do to help with this?

I originally posted about this on the fabulously optimized Discord and I was linked to this issue.

@mrjasonn I think I found a fix. I can't test it tho due to not owning a mac. Can you test it: https://upload.raphimc.net/u/XI8WKg.jar

And also upload screenshots of F3 with and without the fix (fix_slow_buffer_upload_on_apple_gpu in the config file) to confirm that the fix is still improving performance (Hypixel lobby or any scene where there is more than just an empty world is a good place to test it)

Thank you for the fix. I tested on my Hypixel SMP where there are not constantly a different number of entities for consistency reasons, and here are the screenshots (keep in mind that because there are not a lot of entities, the fps is similar with and without fast buffer):

With

Without

There are zero entities in this scene. You could download this map https://www.planetminecraft.com/project/minecraft-benchmark-v3/ and test with/without the fix (Let FPS stabilize for a minute before taking the screenshot). I just need to know if the fix is even still needed and if it is working properly

There are zero entities in this scene. You could download this map https://www.planetminecraft.com/project/minecraft-benchmark-v3/ and test with/without the fix (Let FPS stabilize for a minute before taking the screenshot). I just need to know if the fix is even still needed and if it is working properly

Done.

With

Without

I am aware that the FPS looks similar, but I would still think that we should keep the fix as it would make a more meaningful impact in places such as big server lobbies with lots of people. The GPU utilisation is also much lower with the fix whilst having a higher frame rate than without the fix, which is nice to see.

Thank you. Seems like the fix is still needed and works (It even achieves higher FPS, despite that more chunks are rendered in the image with the fix enabled compared to the one with the fix disabled).