Misaki
d8a7b07624
- Refactor D3D12 backend and RenderGraph module - Update graphics RHI and core rendering components - Add Random.hlsl shader include - Regenerate API documentation and update user guides
54 lines
2.3 KiB
Markdown
54 lines
2.3 KiB
Markdown
# Performance and Memory
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GhostEngine's ECS is explicitly designed around maximum CPU efficiency and AOT compatibility.
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## Structure of Arrays (SoA)
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Traditional OOP patterns use Arrays of Structures (AoS), which causes cache misses when looping through objects to read a single field.
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GhostEngine ECS uses Structure of Arrays (SoA) at the chunk level. A 16KB unmanaged `Chunk` separates components into continuous blocks. When a `System` iterates a `ChunkView` and calls `GetComponentData<Position>()`, it receives a contiguous `Span<Position>`.
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Because modern CPUs pre-fetch continuous memory aggressively, an ECS query can be up to orders of magnitude faster than naive OOP equivalents.
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## Benchmark Example
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The internal `Ghost.Entities.Test` benchmarks demonstrate the raw speed comparison:
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```csharp
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// OOP Approach (~4000ns)
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for (var i = 0; i < _gameObjects.Length; i++)
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{
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_gameObjects[i].Position += new Vector4(_dt, _dt, _dt, 0);
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}
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// ECS Approach (~620ns)
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ref var query = ref _world.ComponentManager.GetEntityQueryReference(_queryIdentifier);
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foreach (var chunkView in query.GetChunkIterator())
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{
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var positions = chunkView.GetComponentDataRW<Position>();
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ref var address = ref MemoryMarshal.GetReference(positions);
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for (var i = 0; i < positions.Length; i++)
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{
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Unsafe.Add(ref address, i).value += new Vector4(_dt, _dt, _dt, 0);
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}
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}
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```
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**Results for 1,000,000 Entities:**
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- Over **98.5% cache hits**
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- Approximately **4x to 6x faster** execution times
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- **0 Bytes** allocated per frame (Zero Garbage Collection)
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## Versioning and Change Tracking
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Chunks maintain atomic version counters. Whenever `GetComponentDataRW<T>()` is called, the chunk updates its component version to match the current `World.Version`.
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Systems can rapidly bypass entire chunks without iterating them by checking `chunkView.HasChanged<T>(LastSystemVersion)`. This enables dirty-flag processing at near-zero cost.
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## Unmanaged Constraints
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To guarantee this performance, the engine strictly enforces unmanaged types.
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- You cannot put `string`, `class`, or managed arrays inside `IComponent`.
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- For bulk temporary allocations during system updates, you should use `VirtualStack.Scope` or `AllocationManager` alongside `UnsafeList<T>` to remain entirely off the .NET Garbage Collector heap.
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