Ferrite

Ferrite

What you get: A performance mod for Minecraft 26.1.2 (mojmap, JDK 25). Built natively against 26.1's deobfuscated source rather than recompiled from the 1.21.11 codebase, so the parity and tick-cost numbers below are measured on 26.1.2 directly. It's a Fabric (Java) mod that calls into native Rust via JNI for the hot paths. Java handles Minecraft integration and mixins, Rust does the heavy per-tick math where the win is big enough to justify crossing the JNI boundary. The 1.21.11 line continues separately on the main branch.

Live now:

• Cramming (/ferrite cramming on|off|status, default on). Rust port of the mob-vs-mob cramming loop. ~65% entity-tick reduction at high mob density. Every MobEntity subclass (villager halls, mob farms). Vanilla 1:1 parity: same push math, same passenger-of-same-vehicle skip, same maxEntityCramming damage (gamerule + 1-in-4 random). /gamerule maxEntityCramming 0 stays at 20 TPS for unbounded farms.
• Redstone (/ferrite redstone ac on). Space Walker's Alternate Current. ~10× fewer cascades, ~6× faster contraptions at same load. Bit-correct on 150,000+ oracle checks, works on existing worlds. Per-cascade Rust BFS adds another ~30% wire-cost cut on heavy builds.
• Hopper extract hint (default on). Per-source-inventory hint tracks the first non-empty slot; extract loops start there instead of iterating from slot 0 every fire. ~23 µs/call at avgStartIdx=16 (~60% reduction), ~110 µs/call at avgStartIdx=53 (~85%) on partially-drained chests. Validator shadow-runs reported 0 stale events across 450+ extracts.
• Hopper highway (/ferrite hopper highway on, default off). Per-slot independent cooldowns + round-robin destination routing. Aggregate per-hopper throughput climbs from vanilla 1/(8 ticks) to up to 5/(8 ticks). 3.1× chain throughput under back-pressure on a 100-hopper test chain. Per-tick item count stays ≤ 1 so comparator transition rate is preserved. For hopper-heavy storage; leave off for sorters tuned to vanilla 8-tick clocks.
• World creation pre-gen (toggle on Create World "More" tab, default off). Pre-generates a configurable 5-50 chunk radius around spawn before the player loads in, runs through Ferrite's optimized chunkgen pipeline. Cancel writes a snapshot, next world load auto-resumes. Boss bar reports progress to the host. Dedicated servers: -Dferrite.pregen.radius=N first-launch only. Validated 53-104 chunks/sec depending on server load (steady ~80/s, ~50/s when competing with active player), TPS 20 holding under flight.
• Density function port: 50/50 bit-exact on 26.1.2 (vs the 41/42 baseline on 1.21.11). Building blocks for the future Rust DF compiler are now in tree.
• Logging gate (/ferrite log monitors on|off|status). Runtime toggle for the periodic monitor reports. About 5 lines/sec across 24 buckets in normal play; turn off on long sessions or I/O-bound hardware to cut log volume without losing the counters.

Logs tick breakdowns every 5s so the next port targets real bottlenecks.

Measured results

Cramming (1000+ active mobs)

metric	vanilla	Ferrite	reduction
tickCramming avg	~14 ms	0.03 ms	~99%
Entity.move() avg	~20 ms	~10 ms	~50% (secondary effect)
total entity tick	~60 ms	~21 ms	~65%

Redstone (lag machine)

metric	vanilla default	Ferrite (AC)	change
cascades per tick	~127,000	~8,250	~15× fewer
gate ticks per tick	~663	~2,780	~4× more
wire cost / gate tick	~0.378 ms	~0.062 ms	~84% less
effective TPS	~4	~5.6	+40%
oracle mismatches	—	0 / 149,669 checked	bit-for-bit correct

Measurement details in CHANGELOG.md and the full investigation path in docs/PROFILING.md in github.

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How it works

Cramming

LivingEntity.tickCramming is intercepted with a Mixin. The first mob's tickCramming call in a given server tick triggers a batch: every mob's position and bounding box is packed into a direct ByteBuffer, Rust builds a 2-block spatial hash, iterates pairs with an array-index guard, applies the vanilla push formula (Chebyshev distance, exact bit-for-bit replica), and returns accumulated (dx, dz) velocity deltas. Java then applies each delta via entity.addVelocity. All subsequent tickCramming calls that tick are cancelled no-ops.

One JNI call per tick. No world state, no snapshot. The win is algorithmic — O(N·k) with spatial hashing where k is local density, instead of vanilla's per-mob level.getEntities(bbox) query-plus-iterate.

Redstone

A @Redirect(NEW) mixin swaps RedstoneWireBlock's redstoneController field from DefaultRedstoneController to FerriteRedstoneController (a subclass) at construction time. With /ferrite redstone ac on, the Ferrite controller routes wire updates through the ported Alternate Current algorithm: build the connected wire network as a graph, find power sources, do one BFS-style settle that touches each wire at most twice, write all power changes in one pass via a chunk-section bypass that skips lighting/heightmap/block-entity bookkeeping. With AC off, the controller delegates to super.update(...) and is byte-for-byte equivalent to vanilla.

Pure Java; no JNI. The win is algorithmic — replacing vanilla's per-wire recursive re-evaluation (which can revisit the same wire dozens of times per cascade) with one settle per cascade, plus skipping the redundant block updates a wire would normally emit between intermediate power levels.

A shadow-compute RedstoneOracle validates every sampled cascade against vanilla's own calculateWirePowerAt, so any algorithm divergence surfaces immediately in [redstone-oracle] log lines.

How to help

If you run mob farms, crowded multiplayer servers, or singleplayer worlds with lots of mobs or animals:

1. Install Ferrite + Fabric API
2. Play normally for 10+ minutes
3. Open .minecraft/logs/latest.log, search for [ferrite]
4. Share representative [cramming-dispatch] and [movement-internals] lines in a GitHub issue or CurseForge comment

Low-end hardware (4-core CPU, integrated graphics) is especially useful — the [chunkgen] and [client-lag] logs on that profile decide what gets optimized next.

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Requirements

• Minecraft 26.1.2 (this build) / Minecraft 1.21.11 (separate main branch builds)
• Java 25 (Temurin recommended; CI builds against JDK 25)
• Fabric Loader 0.18.4+
• Fabric API 0.147.0+26.1.2
• Works in singleplayer and multiplayer
• Server-side compatible, can be installed on a server without requiring players to have the mod

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Platform verification

platform	status
Windows x86_64	✅ Developed and tested throughout
Linux x86_64	✅ Verified — WSL Ubuntu 24.04, OpenJDK 21, server loads /tmp/rust_mod_*.so, initEngine returns Rayon pool size, reaches "Done" with no errors
macOS (universal)	⚠️ Binary confirmed structurally correct (lipo -info shows both x86_64 + arm64 slices); runtime load not yet verified on real Apple hardware

The macOS .dylib is a fat binary produced by lipo -create on the CI macos-latest runner. Happy to mark it verified once a Mac user confirms System.load succeeds — a log snippet showing Loaded rust_mod from /tmp/rust_mod_*.dylib is enough.

The native library is bundled for Windows, Linux, and macOS. If it fails to load on your platform, Ferrite falls back to vanilla behavior automatically — no crashes, no broken worlds. ARM Linux isn't bundled yet.

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Credits

• The redstone wire algorithm is adapted from Space Walker's Alternate Current (MIT). Full attribution in LICENSES.md. The port is Yarn-remapped for 1.21.11 and installed transparently as a DefaultRedstoneController subclass; design and algorithm remain entirely Space Walker's.
• The JNI / native-loading scaffolding was originally forked from Brayan-724/rust-mod-probe — the PoC that demonstrated calling Rust from Fabric.

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License

MIT