Iris 1.7.1 for Versions 1.21 and 1.20.5&6 very poor performance
I've been using Iris shaders since 1.20.1 and until/including 1.20.4 I've had great performance (150-160FPS). Since 1.20.5 the performance has been very poor (9-12FPS) and I don't know why. I assumed it had something to do with the devs wanting to wait until 1.21 and then fix the performance or smth (that's why I waited on saying anything), but nothing has changed.
The only mods I'm running in both versions are:
The shader seen in both screenshots is Complementary Reimagined (unchanged, set to: medium; integrated PBR+).
I am not running any resource packs, plain vanilla.
Both screenshots are made on the same seed, newly generated for each version. I've made sure that I've been in each world for long enough so that minecraft isn't generating new chunks anymore.
The game is set to 16 chunks render & simulation distance.
Minecraft was running with 90 FOV.
My resolution is 1440p.
PC stats:
Does anyone know of any fixes to this problem?
Devs, does this help or do you need more information?
The only mods I'm running in both versions are:
- Iris
- Fabric
- Sodium
The shader seen in both screenshots is Complementary Reimagined (unchanged, set to: medium; integrated PBR+).
I am not running any resource packs, plain vanilla.
Both screenshots are made on the same seed, newly generated for each version. I've made sure that I've been in each world for long enough so that minecraft isn't generating new chunks anymore.
The game is set to 16 chunks render & simulation distance.
Minecraft was running with 90 FOV.
My resolution is 1440p.
PC stats:
- 12th Gen Intel Core i5-12600K 3.69 GHz
- Windows 10 Pro
- 16gb Ram (of which I've given minecraft 8gb for both versions)
- AMD Radeon RX 6800 XT
(I've had to force windows to treat the javaw file as high priority a while back so minecraft actually uses the graphics card)
Does anyone know of any fixes to this problem?
Devs, does this help or do you need more information?


Solution
I've figured it out!
In the video it was enough to set the javaw file to high performance. Since 1.20.5 one has to set the other java file named java in that folder to high performance too.
In the video it was enough to set the javaw file to high performance. Since 1.20.5 one has to set the other java file named java in that folder to high performance too.