Overview

This repository contains performance benchmarks comparing several Rust Entity-Component-System (ECS) libraries using Criterion. We evaluate common operations across Bevy ECS, Hecs, Flecs ECS, Legion, and Specs to understand their relative strengths and trade-offs.

The five benchmark scenarios are:

1. Spawn – measuring raw entity creation cost (100,000 entities).
2. Simple Iteration – spawning entities with Position and Velocity and performing a simple update loop.
3. Fragmented Iteration – spawning a few types of components (A, B, C, Data) to simulate data fragmentation, then iterating over one component.
4. Heavy Compute – spawning entities with a Transform matrix and performing a CPU-heavy inner loop per entity.
5. CRUD Add/Remove – measuring the cost of adding and removing a component (B) on entities that already have another component (A).

Each section below embeds the violin plot generated by Criterion, highlighting the distribution of iteration times for that test.

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1. Spawn Benchmark

Entities Created: 100,000

This chart shows the distribution of times taken to spawn 100,000 entities for each ECS implementation.

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2. Simple Iteration Benchmark

Operations:

• Spawn 100,000 entities with Position and Velocity.
• Iterate and update each Position by its corresponding Velocity.

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3. Fragmented Iteration Benchmark

Setup:

• Spawn FRAGMENTED_ENTITIES_PER_TYPE entities per component type (A, B, C) each paired with Data.
• Iterate over all Data components and perform a simple multiplication.

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4. Heavy Compute Benchmark

Setup:

• Spawn 1,000 entities with a 4×4 Transform matrix.
• Perform HEAVY_COMPUTE_ITERATIONS (100) inner-loop additions on the first element of the matrix.

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5. CRUD Add/Remove Benchmark

Operations:

• Spawn 100,000 entities with component A.
• Add component B to each entity.
• Remove component B from each entity.

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Running the Benchmarks

Run all benchmarks with:

cargo bench

Results will appear in the target/criterion directory.