[Feature]: FP8 Quantization Support for DiT (#1034)

Signed-off-by: lishunyang <lishunyang12@163.com>
Signed-off-by: SYLAR <125541396+lishunyang12@users.noreply.github.com>

docs/user_guide/diffusion/quantization/fp8.md

@@ -0,0 +1,77 @@
+# FP8 Quantization
+
+## Overview
+
+FP8 quantization converts BF16/FP16 weights to FP8 at model load time. No calibration or pre-quantized checkpoint needed.
+
+Depending on the model, either all layers can be quantized, or some sensitive layers should stay in BF16. See the [per-model table](#supported-models) for which case applies.
+
+Common sensitive layers in DiT-based diffusion models include **image-stream MLPs** (`img_mlp`). These are particularly vulnerable to FP8 precision loss because they process denoising latents whose dynamic range shifts significantly across timesteps, and unlike attention projections (which benefit from QK-Norm stabilization), MLPs have no built-in normalization to absorb quantization error. In deep architectures (e.g., 60+ residual blocks), small per-layer errors compound and degrade output quality. Other layers such as **attention projections** (`to_qkv`, `to_out`) and **text-stream MLPs** (`txt_mlp`) are generally more robust due to normalization or more stable input statistics.
+
+## Configuration
+
+1. **Python API**: set `quantization="fp8"`. To skip sensitive layers, use `quantization_config` with `ignored_layers`.
+
+```python
+from vllm_omni import Omni
+from vllm_omni.inputs.data import OmniDiffusionSamplingParams
+
+# All layers quantized
+omni = Omni(model="<your-model>", quantization="fp8")
+
+# Skip sensitive layers
+omni = Omni(
+    model="<your-model>",
+    quantization_config={
+        "method": "fp8",
+        "ignored_layers": ["<layer-name>"],
+    },
+)
+
+outputs = omni.generate(
+    "A cat sitting on a windowsill",
+    OmniDiffusionSamplingParams(num_inference_steps=50),
+)
+```
+
+2. **CLI**: pass `--quantization fp8` and optionally `--ignored-layers`.
+
+```bash
+# All layers
+python text_to_image.py --model <your-model> --quantization fp8
+
+# Skip sensitive layers
+python text_to_image.py --model <your-model> --quantization fp8 --ignored-layers "img_mlp"
+
+# Online serving
+vllm serve <your-model> --omni --quantization fp8
+```
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `method` | str | — | Quantization method (`"fp8"`) |
+| `ignored_layers` | list[str] | `[]` | Layer name patterns to keep in BF16 |
+| `activation_scheme` | str | `"dynamic"` | `"dynamic"` (no calibration) or `"static"` |
+| `weight_block_size` | list[int] \| None | `None` | Block size for block-wise weight quantization |
+
+The available `ignored_layers` names depend on the model architecture (e.g., `to_qkv`, `to_out`, `img_mlp`, `txt_mlp`). Consult the transformer source for your target model.
+
+## Supported Models
+
+| Model | HF Models | Recommendation | `ignored_layers` |
+|-------|-----------|---------------|------------------|
+| Z-Image | `Tongyi-MAI/Z-Image-Turbo` | All layers | None |
+| Qwen-Image | `Qwen/Qwen-Image`, `Qwen/Qwen-Image-2512` | Skip sensitive layers | `img_mlp` |
+
+## Combining with Other Features
+
+FP8 quantization can be combined with cache acceleration:
+
+```python
+omni = Omni(
+    model="<your-model>",
+    quantization="fp8",
+    cache_backend="tea_cache",
+    cache_config={"rel_l1_thresh": 0.2},
+)
+```

docs/user_guide/diffusion/quantization/overview.md

@@ -0,0 +1,17 @@
+# Quantization for Diffusion Transformers
+
+vLLM-Omni supports quantization of DiT linear layers to reduce memory usage and accelerate inference.
+
+## Supported Methods
+
+| Method | Guide |
+|--------|-------|
+| FP8 | [FP8](fp8.md) |
+
+## Device Compatibility
+
+| GPU Generation | Example GPUs | FP8 Mode |
+|---------------|-------------------|----------|
+| Ada/Hopper (SM 89+) | RTX 4090, H100, H200 | Full W8A8 with native hardware |
+
+Kernel selection is automatic.

docs/user_guide/diffusion_acceleration.md

@@ -1,6 +1,6 @@
 # Diffusion Acceleration Overview
 
-vLLM-Omni supports various cache acceleration methods to speed up diffusion model inference with minimal quality degradation. These methods include **cache methods** that intelligently cache intermediate computations to avoid redundant work across diffusion timesteps, and **parallelism methods** that distribute the computation across multiple devices.
+vLLM-Omni supports various acceleration methods to speed up diffusion model inference with minimal quality degradation. These include **cache methods** that intelligently cache intermediate computations to avoid redundant work across diffusion timesteps, **parallelism methods** that distribute the computation across multiple devices, and **quantization methods** that reduce memory footprint while preserving accuracy.
 
 ## Supported Acceleration Methods
 
@@ -14,6 +14,10 @@ vLLM-Omni currently supports two main cache acceleration backends:
 
 Both methods can provide significant speedups (typically **1.5x-2.0x**) while maintaining high output quality.
 
+vLLM-Omni also supports quantization methods:
+
+3. **[FP8 Quantization](diffusion/quantization/overview.md)** - Reduces DiT linear layers from BF16 to FP8, providing ~1.28x speedup with minimal quality loss. Supports per-layer skip for sensitive layers.
+
 vLLM-Omni also supports parallelism methods for diffusion models, including:
 
 1. [Ulysses-SP](diffusion/parallelism_acceleration.md#ulysses-sp) - splits the input along the sequence dimension and uses all-to-all communication to allow each device to compute only a subset of attention heads.
@@ -35,6 +39,12 @@ vLLM-Omni also supports parallelism methods for diffusion models, including:
 | **TeaCache** | `cache_backend="tea_cache"` | Simple, adaptive caching with minimal configuration | Quick setup, balanced speed/quality |
 | **Cache-DiT** | `cache_backend="cache_dit"` | Advanced caching with multiple techniques (DBCache, TaylorSeer, SCM) | Maximum acceleration, fine-grained control |
 
+### Quantization Methods
+
+| Method | Configuration | Description | Best For |
+|--------|--------------|-------------|----------|
+| **FP8** | `quantization="fp8"` | FP8 W8A8 on Ada/Hopper, weight-only on older GPUs | Memory reduction, inference speedup |
+
 ## Supported Models
 
 The following table shows which models are currently supported by each acceleration method:
@@ -58,10 +68,18 @@ The following table shows which models are currently supported by each accelerat
 
 ### VideoGen
 
-| Model | Model Identifier | TeaCache | Cache-DiT | Ulysses-SP | Ring-Attention |CFG-Parallel |
+| Model | Model Identifier | TeaCache | Cache-DiT | Ulysses-SP | Ring-Attention | CFG-Parallel |
 |-------|------------------|:--------:|:---------:|:----------:|:--------------:|:----------------:|
 | **Wan2.2** | `Wan-AI/Wan2.2-T2V-A14B-Diffusers` | ❌ | ✅ | ✅ | ✅ | ✅ |
 
+### Quantization
+
+| Model | Model Identifier | FP8 |
+|-------|------------------|:---:|
+| **Qwen-Image** | `Qwen/Qwen-Image` | ✅ |
+| **Qwen-Image-2512** | `Qwen/Qwen-Image-2512` | ✅ |
+| **Z-Image** | `Tongyi-MAI/Z-Image-Turbo` | ✅ |
+
 
 ## Performance Benchmarks
 
@@ -272,12 +290,30 @@ outputs = omni.generate(
 )
 ```
 
+### Using FP8 Quantization
+
+```python
+from vllm_omni import Omni
+from vllm_omni.inputs.data import OmniDiffusionSamplingParams
+
+omni = Omni(
+    model="<your-model>",
+    quantization="fp8",
+)
+
+outputs = omni.generate(
+    "A cat sitting on a windowsill",
+    OmniDiffusionSamplingParams(num_inference_steps=50),
+)
+```
+
 ## Documentation
 
 For detailed information on each acceleration method:
 
 - **[TeaCache Guide](diffusion/teacache.md)** - Complete TeaCache documentation, configuration options, and best practices
 - **[Cache-DiT Acceleration Guide](diffusion/cache_dit_acceleration.md)** - Comprehensive Cache-DiT guide covering DBCache, TaylorSeer, SCM, and configuration parameters
+- **[FP8 Quantization Guide](diffusion/quantization/overview.md)** - FP8 quantization for DiT models with per-layer control
 - **[Tensor Parallelism](diffusion/parallelism_acceleration.md#tensor-parallelism)** - Guidance on how to enable TP for diffusion models.
 - **[Sequence Parallelism](diffusion/parallelism_acceleration.md#sequence-parallelism)** - Guidance on how to set sequence parallelism with configuration.
 - **[CFG-Parallel](diffusion/parallelism_acceleration.md#cfg-parallel)** - Guidance on how to set CFG-Parallel to run positive/negative branches across ranks.