Hey youll prob never respond because its afew years later but did u ever figure this out... im having identical issues and im still playing on 1.12.2 so i shouldnt be too far ahead version wise. Anyway ye i literally cant run minecraft with more than 30-40 mods before it starts dropping to like 30 fps and without shaders and those more i can run minecraft at like 1000+ with shaders and without mods i can run at 300+ but with mods it drops significantly which i get but not really because theres no difference in how it looks othwr than shaders and my pc isnt even close to getting near even 50% used on any spec so ye i have 0 clue why it lags. I would think ram but i add more ram and it ether doesnt do anything or it lags more because it then has a bigger garbage collector... i just wanna run a modpack without lagging like i have a crazy good pc and should be able to run 60 fps on mc like i can run 150 fps on destiny full graphics which looks crazy good yet i cant run mc above 30 fps and it looks like blocks
Hey, yeah well I now have a completely new computer now but I do know how to solve these isssues. First off, 1.12.2 isn't as optimized as newer forge versions, so it already is on a lower level. my advice would be to install performance mods (my go to combo is optifine, TexFix, betterfps, vanillafix, unloader, and performant if it is compatible with the rest of the mods), and just try removing mods like recurrent complex or similar large structure mods (in older versions they can make a lot of lag occur.) if you just want to post your mod list I can see if I can figure it out, too.
Let me know if you need any more help, and happy holidays if you celebrate :D
So ye im basically only on 1.12.2 because of tektopia, my whole modpack revolves around that mod. i do know that mod has some lag but it cant be the main source because even without the mod its just not performing. i also have better fps, vanilla fix, phosphor, optifine obviously, foam fix. but ye i have abunch of other mods that cause lag but ive seen other people play modpacks with these mods and not have any problem on like a 1080ti, and i have a 2070 super with 32 gb of ram and a ryzen 5 3800x so like im so confused my computer isnt bad by any means and ye idk i tried downscaling how many mods but at like 30 mods (including like secondary mods and performance mods) it starts dropping to 30 fps then at 50 mods its at 10-30... like maybe it will hit 50 fps for like a second but ye idk i wish there was a way to make minecraft actually utilize my pc..... when i open task manager it says like 10 % cpu 20-30% gpu and so on.... idk it shouldnt be lagging if its not even using my hardware
How many cores are designated in your java arguments? (the "UseG1GC" in the arguments means you are use one core.)
Are you using OpenJ9 java or the bundled/default one?
Have you set forge's force threaded chunk rendering option to true?
What settings do you have in you options? (render distance, max fps, smooth lighting, details, animations, performance, etc.)
Have you ever run BetterFPS' jar file, ran the "test algorithms" option, and changed to the algorithm it recommends? (this one is super important)
I have managed to solve most of these problems through lots of tinkering. I ended up moving on from 1.12.2 for the most part because 1.16.4 runs better and many newer mods wont backport to 1.12.2. I am still waiting for a village management/colony mod that isnt as extremely buggy or laggy as tektopia or MineColonies, maybe one day someone will make one. If Tektopia ever updates to a newer version, or a decent alternative to it comes out on newer versions, I highly recommend moving forward. For now I will try to help you however I can with this.