chore: import upstream snapshot with attribution

docs/diffusion/performance/cache/cache_dit.md

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+# Cache-DiT
+
+SGLang integrates [Cache-DiT](https://github.com/vipshop/cache-dit), a caching acceleration engine for Diffusion Transformers (DiT), to achieve up to **1.69x inference speedup** with minimal quality loss.
+
+## Overview
+
+**Cache-DiT** uses intelligent caching strategies to skip redundant computation in the denoising loop:
+
+- **DBCache (Dual Block Cache)**: Dynamically decides when to cache transformer blocks based on residual differences
+- **TaylorSeer**: Uses Taylor expansion for calibration to optimize caching decisions
+- **SCM (Step Computation Masking)**: Step-level caching control for additional speedup
+
+## Basic Usage
+
+Enable Cache-DiT by exporting the environment variable and using `sglang generate` or `sglang serve` :
+
+```bash
+SGLANG_CACHE_DIT_ENABLED=true \
+sglang generate --model-path Qwen/Qwen-Image \
+    --prompt "A beautiful sunset over the mountains"
+```
+
+## Diffusers Backend
+
+Cache-DiT supports loading acceleration configs from a custom YAML file. For
+diffusers pipelines (`diffusers` backend), pass the YAML/JSON path via `--cache-dit-config`. This
+flow requires cache-dit >= 1.2.0 (`cache_dit.load_configs`).
+
+### Single GPU inference
+
+Define a `cache.yaml` file that contains:
+
+- DBCache + TaylorSeer
+
+```yaml
+cache_config:
+  max_warmup_steps: 8
+  warmup_interval: 2
+  max_cached_steps: -1
+  max_continuous_cached_steps: 2
+  Fn_compute_blocks: 1
+  Bn_compute_blocks: 0
+  residual_diff_threshold: 0.12
+  enable_taylorseer: true
+  taylorseer_order: 1
+```
+
+Then apply the config with:
+
+```bash
+sglang generate \
+  --backend diffusers \
+  --model-path Qwen/Qwen-Image \
+  --cache-dit-config cache.yaml \
+  --prompt "A beautiful sunset over the mountains"
+```
+
+- DBCache + TaylorSeer + SCM (Step Computation Mask)
+
+```yaml
+cache_config:
+  max_warmup_steps: 8
+  warmup_interval: 2
+  max_cached_steps: -1
+  max_continuous_cached_steps: 2
+  Fn_compute_blocks: 1
+  Bn_compute_blocks: 0
+  residual_diff_threshold: 0.12
+  enable_taylorseer: true
+  taylorseer_order: 1
+  # Must set the num_inference_steps for SCM. The SCM will automatically
+  # generate the steps computation mask based on the num_inference_steps.
+  # Reference: https://cache-dit.readthedocs.io/en/latest/user_guide/CACHE_API/#scm-steps-computation-masking
+  num_inference_steps: 28
+  steps_computation_mask: fast
+```
+
+- DBCache + TaylorSeer + SCM (Step Computation Mask) + Cache CFG
+
+```yaml
+cache_config:
+  max_warmup_steps: 8
+  warmup_interval: 2
+  max_cached_steps: -1
+  max_continuous_cached_steps: 2
+  Fn_compute_blocks: 1
+  Bn_compute_blocks: 0
+  residual_diff_threshold: 0.12
+  enable_taylorseer: true
+  taylorseer_order: 1
+  num_inference_steps: 28
+  steps_computation_mask: fast
+  enable_sperate_cfg: true # e.g, Qwen-Image, Wan, Chroma, Ovis-Image, etc.
+```
+
+### Distributed inference
+
+- 1D Parallelism
+
+Define a parallelism only config yaml `parallel.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+```
+
+Then, apply the distributed inference acceleration config from yaml. `ulysses_size: auto` means that cache-dit will auto detect the `world_size` as the ulysses_size. Otherwise, you should manually set it as specific int number, e.g, 4.
+
+Then apply the distributed config with: (Note: please add `--num-gpus N` to specify the number of gpus for distributed inference)
+
+```bash
+sglang generate \
+  --backend diffusers \
+  --num-gpus 4 \
+  --model-path Qwen/Qwen-Image \
+  --cache-dit-config parallel.yaml \
+  --prompt "A futuristic cityscape at sunset"
+```
+
+- 2D Parallelism
+
+You can also define a 2D parallelism config yaml `parallel_2d.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  tp_size: 2
+  attention_backend: native
+```
+Then, apply the 2D parallelism config from yaml. Here `tp_size: 2` means using tensor parallelism with size 2. The `ulysses_size: auto` means that cache-dit will auto detect the `world_size // tp_size` as the ulysses_size.
+
+- 3D Parallelism
+
+You can also define a 3D parallelism config yaml `parallel_3d.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: 2
+  ring_size: 2
+  tp_size: 2
+  attention_backend: native
+```
+Then, apply the 3D parallelism config from yaml. Here `ulysses_size: 2`, `ring_size: 2`, `tp_size: 2` means using ulysses parallelism with size 2, ring parallelism with size 2 and tensor parallelism with size 2.
+
+- Ulysses Anything Attention
+
+To enable Ulysses Anything Attention, you can define a parallelism config yaml `parallel_uaa.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  ulysses_anything: true
+```
+
+- Ulysses FP8 Communication
+
+For device that don't have NVLink support, you can enable Ulysses FP8 Communication to further reduce the communication overhead. You can define a parallelism config yaml `parallel_fp8.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  ulysses_float8: true
+```
+
+- Async Ulysses CP
+
+You can also enable async ulysses CP to overlap the communication and computation. Define a parallelism config yaml `parallel_async.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  ulysses_async: true # Now, only support for FLUX.1, Qwen-Image, Ovis-Image and Z-Image.
+```
+Then, apply the config from yaml. Here `ulysses_async: true` means enabling async ulysses CP.
+
+- TE-P and VAE-P
+
+You can also specify the extra parallel modules in the yaml config. For example, define a parallelism config yaml `parallel_extra.yaml` file that contains:
+
+```yaml
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  extra_parallel_modules: ["text_encoder", "vae"]
+```
+
+
+### Hybrid Cache and Parallelism
+
+Define a hybrid cache and parallel acceleration config yaml `hybrid.yaml` file that contains:
+
+```yaml
+cache_config:
+  max_warmup_steps: 8
+  warmup_interval: 2
+  max_cached_steps: -1
+  max_continuous_cached_steps: 2
+  Fn_compute_blocks: 1
+  Bn_compute_blocks: 0
+  residual_diff_threshold: 0.12
+  enable_taylorseer: true
+  taylorseer_order: 1
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  extra_parallel_modules: ["text_encoder", "vae"]
+```
+
+Then, apply the hybrid cache and parallel acceleration config from yaml.
+
+```bash
+sglang generate \
+  --backend diffusers \
+  --num-gpus 4 \
+  --model-path Qwen/Qwen-Image \
+  --cache-dit-config hybrid.yaml \
+  --prompt "A beautiful sunset over the mountains"
+```
+
+### Attention Backend
+
+In some cases, users may want to only specify the attention backend without any other optimization configs. In this case, you can define a yaml file `attention.yaml` that only contains:
+
+```yaml
+attention_backend: "flash" # '_flash_3' for Hopper
+```
+
+### Quantization
+
+You can also specify the quantization config in the yaml file, required `torchao>=0.16.0`. For example, define a yaml file `quantize.yaml` that contains:
+
+```yaml
+quantize_config: # quantization configuration for transformer modules
+  # float8 (DQ), float8_weight_only, float8_blockwise, int8 (DQ), int8_weight_only, etc.
+  quant_type: "float8"
+  # layers to exclude from quantization (transformer). layers that contains any of the
+  # keywords in the exclude_layers list will be excluded from quantization. This is useful
+  # for some sensitive layers that are not robust to quantization, e.g., embedding layers.
+  exclude_layers:
+    - "embedder"
+    - "embed"
+  verbose: false # whether to print verbose logs during quantization
+```
+Then, apply the quantization config from yaml. Please also enable torch.compile for better performance if you are using quantization. For example:
+
+```bash
+sglang generate \
+  --backend diffusers \
+  --model-path Qwen/Qwen-Image \
+  --warmup \
+  --cache-dit-config quantize.yaml \
+  --enable-torch-compile \
+  --dit-cpu-offload false \
+  --text-encoder-cpu-offload false \
+  --prompt "A beautiful sunset over the mountains"
+```
+
+### Combined Configs: Cache + Parallelism + Quantization
+
+You can also combine all the above configs together in a single yaml file `combined.yaml` that contains:
+
+```yaml
+cache_config:
+  max_warmup_steps: 8
+  warmup_interval: 2
+  max_cached_steps: -1
+  max_continuous_cached_steps: 2
+  Fn_compute_blocks: 1
+  Bn_compute_blocks: 0
+  residual_diff_threshold: 0.12
+  enable_taylorseer: true
+  taylorseer_order: 1
+parallelism_config:
+  ulysses_size: auto
+  attention_backend: native
+  extra_parallel_modules: ["text_encoder", "vae"]
+quantize_config:
+  quant_type: "float8"
+  exclude_layers:
+    - "embedder"
+    - "embed"
+  verbose: false
+```
+Then, apply the combined cache, parallelism and quantization config from yaml. Please also enable torch.compile for better performance if you are using quantization.
+
+## Advanced Configuration
+
+### DBCache Parameters
+
+DBCache controls block-level caching behavior:
+
+| Parameter | Env Variable              | Default | Description                              |
+|-----------|---------------------------|---------|------------------------------------------|
+| Fn        | `SGLANG_CACHE_DIT_FN`     | 1       | Number of first blocks to always compute |
+| Bn        | `SGLANG_CACHE_DIT_BN`     | 0       | Number of last blocks to always compute  |
+| W         | `SGLANG_CACHE_DIT_WARMUP` | 4       | Warmup steps before caching starts       |
+| R         | `SGLANG_CACHE_DIT_RDT`    | 0.24    | Residual difference threshold            |
+| MC        | `SGLANG_CACHE_DIT_MC`     | 3       | Maximum continuous cached steps          |
+
+### TaylorSeer Configuration
+
+TaylorSeer improves caching accuracy using Taylor expansion:
+
+| Parameter | Env Variable                  | Default | Description                     |
+|-----------|-------------------------------|---------|---------------------------------|
+| Enable    | `SGLANG_CACHE_DIT_TAYLORSEER` | false   | Enable TaylorSeer calibrator    |
+| Order     | `SGLANG_CACHE_DIT_TS_ORDER`   | 1       | Taylor expansion order (1 or 2) |
+
+### Combined Configuration Example
+
+DBCache and TaylorSeer are complementary strategies that work together, you can configure both sets of parameters
+simultaneously:
+
+```bash
+SGLANG_CACHE_DIT_ENABLED=true \
+SGLANG_CACHE_DIT_FN=2 \
+SGLANG_CACHE_DIT_BN=1 \
+SGLANG_CACHE_DIT_WARMUP=4 \
+SGLANG_CACHE_DIT_RDT=0.4 \
+SGLANG_CACHE_DIT_MC=4 \
+SGLANG_CACHE_DIT_TAYLORSEER=true \
+SGLANG_CACHE_DIT_TS_ORDER=2 \
+sglang generate --model-path black-forest-labs/FLUX.1-dev \
+    --prompt "A curious raccoon in a forest"
+```
+
+### SCM (Step Computation Masking)
+
+SCM provides step-level caching control for additional speedup. It decides which denoising steps to compute fully and
+which to use cached results.
+
+**SCM Presets**
+
+SCM is configured with presets:
+
+| Preset   | Compute Ratio | Speed    | Quality    |
+|----------|---------------|----------|------------|
+| `none`   | 100%          | Baseline | Best       |
+| `slow`   | ~75%          | ~1.3x    | High       |
+| `medium` | ~50%          | ~2x      | Good       |
+| `fast`   | ~35%          | ~3x      | Acceptable |
+| `ultra`  | ~25%          | ~4x      | Lower      |
+
+**Usage**
+
+```bash
+SGLANG_CACHE_DIT_ENABLED=true \
+SGLANG_CACHE_DIT_SCM_PRESET=medium \
+sglang generate --model-path Qwen/Qwen-Image \
+    --prompt "A futuristic cityscape at sunset"
+```
+
+**Custom SCM Bins**
+
+For fine-grained control over which steps to compute vs cache:
+
+```bash
+SGLANG_CACHE_DIT_ENABLED=true \
+SGLANG_CACHE_DIT_SCM_COMPUTE_BINS="8,3,3,2,2" \
+SGLANG_CACHE_DIT_SCM_CACHE_BINS="1,2,2,2,3" \
+sglang generate --model-path Qwen/Qwen-Image \
+    --prompt "A futuristic cityscape at sunset"
+```
+
+**SCM Policy**
+
+| Policy    | Env Variable                          | Description                                 |
+|-----------|---------------------------------------|---------------------------------------------|
+| `dynamic` | `SGLANG_CACHE_DIT_SCM_POLICY=dynamic` | Adaptive caching based on content (default) |
+| `static`  | `SGLANG_CACHE_DIT_SCM_POLICY=static`  | Fixed caching pattern                       |
+
+## Environment Variables
+
+All Cache-DiT parameters can be configured via environment variables.
+See [Environment Variables](../../environment_variables.md) for the complete list.
+
+## Supported Models
+
+SGLang Diffusion x Cache-DiT supports almost all models originally supported in SGLang Diffusion:
+
+| Model Family | Example Models              |
+|--------------|-----------------------------|
+| Wan          | Wan2.1, Wan2.2              |
+| Flux         | FLUX.1-dev, FLUX.2-dev      |
+| Z-Image      | Z-Image-Turbo               |
+| Qwen         | Qwen-Image, Qwen-Image-Edit |
+| Hunyuan      | HunyuanVideo                |
+
+## Performance Tips
+
+1. **Start with defaults**: The default parameters work well for most models
+2. **Use TaylorSeer**: It typically improves both speed and quality
+3. **Tune R threshold**: Lower values = better quality, higher values = faster
+4. **SCM for extra speed**: Use `medium` preset for good speed/quality balance
+5. **Warmup matters**: Higher warmup = more stable caching decisions
+
+## Limitations
+
+- **SGLang-native pipelines**: Distributed support (TP/SP) is not yet validated; Cache-DiT will be automatically
+  disabled when `world_size > 1`.
+- **SCM minimum steps**: SCM requires >= 8 inference steps to be effective
+- **Model support**: Only models registered in Cache-DiT's BlockAdapterRegister are supported
+
+## Troubleshooting
+
+### SCM disabled for low step count
+
+For models with < 8 inference steps (e.g., DMD distilled models), SCM will be automatically disabled. DBCache
+acceleration still works.
+
+## References
+
+- [Cache-DiT](https://github.com/vipshop/cache-dit)
+- [SGLang Diffusion](../index.md)