Int8 Quantization Support for DiT (Z-Image & Qwen-Image) (#1470)

Signed-off-by: juboyu <767868009@qq.com>
Signed-off-by: JuboYu <767868009@qq.com>
Signed-off-by: Alicia <115451386+congw729@users.noreply.github.com>
Co-authored-by: Alicia <115451386+congw729@users.noreply.github.com>
Co-authored-by: WeiQing Chen <40507679+david6666666@users.noreply.github.com>

docs/user_guide/diffusion/quantization/int8.md

@@ -0,0 +1,75 @@
+# Int8 Quantization
+
+## Overview
+
+Int8 quantization converts BF16/FP16 weights to Int8 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/FP16. See the [per-model table](#supported-models) for which case applies.
+
+## Configuration
+
+1. **Python API**: set `quantization="int8"`. 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="int8")
+
+# Skip sensitive layers
+omni = Omni(
+    model="<your-model>",
+    quantization_config={
+        "method": "int8",
+        "ignored_layers": ["<layer-name>"],
+    },
+)
+
+outputs = omni.generate(
+    "A cat sitting on a windowsill",
+    OmniDiffusionSamplingParams(num_inference_steps=50),
+)
+```
+
+2. **CLI**: pass `--quantization int8` and optionally `--ignored-layers`.
+
+```bash
+# All layers
+python text_to_image.py --model <your-model> --quantization int8
+
+# Skip sensitive layers
+python text_to_image.py --model <your-model> --quantization int8 --ignored-layers "img_mlp"
+
+# Online serving
+vllm serve <your-model> --omni --quantization int8
+```
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `method` | str | — | Quantization method (`"int8"`) |
+| `ignored_layers` | list[str] | `[]` | Layer name patterns to keep in BF16/FP16 |
+| `activation_scheme` | str | `"dynamic"` | `"dynamic"` (no calibration) |
+
+
+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` | All layers | None |
+
+## Combining with Other Features
+
+Int8 quantization can be combined with cache acceleration:
+
+```python
+omni = Omni(
+    model="<your-model>",
+    quantization="int8",
+    cache_backend="tea_cache",
+    cache_config={"rel_l1_thresh": 0.2},
+)
+```

docs/user_guide/diffusion/quantization/overview.md

@@ -7,12 +7,20 @@ vLLM-Omni supports quantization of DiT linear layers to reduce memory usage and
 | Method | Guide |
 |--------|-------|
 | FP8 | [FP8](fp8.md) |
+| Int8 | [Int8](int8.md) |
 | GGUF | [GGUF](gguf.md) |
 
-## Device Compatibility
+## Device Compatibility for FP8
 
 | GPU Generation | Example GPUs | FP8 Mode |
 |---------------|-------------------|----------|
 | Ada/Hopper (SM 89+) | RTX 4090, H100, H200 | Full W8A8 with native hardware |
 
 Kernel selection is automatic.
+
+## Device Compatibility for Int8
+
+| Device Type | Generation | Example | Int8 Mode |
+|-------------|---------------|-------------------|----------|
+| NVIDIA GPU | Ada/Hopper (SM 89+) | RTX 4090, H100, H200 | Full W8A8 with native hardware |
+| Ascend NPU | Atlas A2/Atlas A3 | Atlas 800T A2/Atlas 900 A3 | Full W8A8 with native hardware |