Increased mouse sensitivity when playing Minecraft

[Oregano1963]

Describe the issue
When using Graal CE 24, the mouse sensitivity increases when playing Minecraft. This is independent of modloader, jvm arguments, and game version.

Steps to reproduce the issue
Please include both build steps as well as run steps

1. Be on NixOS
2. Download Prism Launcher (prismlauncher)
3. Download Graal CE 24 (graalvmPackages.graalvm-ce)
4. Go to any version, any modpack, and make a world.
5. Move your mouse around using regular java (provided by launcher) and with Graal CE

Describe GraalVM and your environment:

• GraalVM version (latest snapshot builds can be found here), or commit id if built from source: CE 24.0.1
• JDK major version: 24
• OS: NixOS 25.05
• Architecture: AMD64

More details
Add any other information about the problem here. Especially important are stack traces or log output. Feel free to link to gists or to screenshots if necessary.

1.21.7 with no mods: https://mclo.gs/mFiPfMb

[davleopo]

Thank you @Oregano1963 for the report. Has been a while since we had a mine minecraft issue. Did you only try on nixos or is it only reproducing on nix?

How long till the sensitivity increases?
Ill have a look.

[Oregano1963]

Thank you @Oregano1963 for the report. Has been a while since we had a mine minecraft issue. Did you only try on nixos or is it only reproducing on nix?

How long till the sensitivity increases? Ill have a look.

I only have NixOS so I've only tried it there. It's never normal when on Graal--it's super sensitive from the moment I enter a world.

[davleopo]

Ok thanks.
Ill try to reproduce it.

Tracked internally as GR-67218 .

[gergo-]

Hi @Oregano1963 , thanks for this bug report. I tried to reproduce this locally, but I can't see the difference in mouse sensitivity. Is this a huge effect that should be immediately obvious to anyone, or do you think one would have to be an experienced Minecraft player who is really used to the game? Is the effect as big as the difference between changing the mouse sensitivity in the options from 100% to hyperspeed? Or even larger? How does it behave if you set the sensitivity to 10%?

I have only tried the demo world so far, can you verify locally that you are also seeing this in the demo world? (I'm not sure if this is easy to try without removing your linked account from the launcher's account manager.)

Just to be sure that we are really testing the same version (if I read the nix package definition correctly, it just downloads one of our packages), could you please post the output of <path to GraalVM>/bin/java -version and <path to GraalVM>/bin/java -Xinternalversion?

I saw from the log you posted that your CPU supports AVX-512 instructions. On the remote chance that this is related, could you try setting -XX:UseAVX=2 in the "Java arguments" field in the launcher properties and see if this makes a difference?

Also, could you please try setting -XX:-UseJVMCICompiler in the "Java arguments" field? This would confirm that disabling the Graal JIT compiler makes the problem go away, i.e., this is related to something the compiler does. (This setting is not meant for day-to-day use since it makes GraalVM behave like a non-Graal VM.)

[gergo-]

Also, forgot to ask: Did you notice this after a recent update to either Minecraft or GraalVM?

[Oregano1963]

Is this a huge effect that should be immediately obvious to anyone

Yes. It's like changing the sensitivity to 130%. Even at 10% sensitivity, it's noticeable.

/bin/java -version:
openjdk version "24.0.1" 2025-04-15
OpenJDK Runtime Environment GraalVM CE 24.0.1+9.1 (build 24.0.1+9-jvmci-b01)
OpenJDK 64-Bit Server VM GraalVM CE 24.0.1+9.1 (build 24.0.1+9-jvmci-b01, mixed mode, sharing)

/bin/java -Xinternalversion:
OpenJDK 64-Bit Server VM (24.0.1+9-jvmci-b01) for linux-amd64 JRE (24.0.1+9-jvmci-b01), built on 2025-03-10T11:12:06Z with gcc 13.2.0

-XX:UseAVX=2 Didn't change the sensitivity
-XX:-UseJVMCICompiler Does make it normal again

I recently downloaded GraalCE--this has nothing to with recent updates to either.

[gergo-]

Thanks for the info, that helps narrow things down a bit.

Yes. It's like changing the sensitivity to 130%.

I was afraid you would say something like this... I find the difference between 100% and 130% really subtle, so I'm not convinced I can pick out the difference. I'll ask around if someone on the team has a keener eye.

In the meantime, if you're motivated, it would be great if you could check if the problem is still present on newer development builds. The newest one is https://github.com/graalvm/graalvm-ce-dev-builds/releases/download/26.0.0-dev-20250708_0030/graalvm-community-java26-linux-amd64-dev.tar.gz.

[gergo-]

@Oregano1963 some team members suggested that the visual difference you're seeing might be related to different frame rates. Have you checked how many FPS you are getting in various configurations? I used a mod called "FPS - Display" to display frame rates. (I was running windowed, with fabulous graphics, VSync off.) On my machine, Oracle GraalVM (formerly known as GraalVM Enterprise Edition) seems to be slightly faster than GraalVM CE and the JDK bundled with the launcher, but I don't think there is a convincing difference between the latter two. Maybe there is one on your machine.

[Oregano1963]

I actually had tried using test builds but Nix isn't FHS compliant so those don't work--they'd have to be packaged specifically for NixOS.

As for framerates, the issue is independent of framerates as I tried with both the default 120fps as well as unlimited (vsync on and off) and 60fps.

I tried on performance pack with Sodium Extras (fps display) and got the same result at multiple framerates.