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Check KV4 compatibility with attention backends and add KV4 support to the attention_backend doc (#14467)

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Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
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Ho-Ren (Jack) Chuang
2025-12-11 19:00:53 -08:00
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parent b62e7e3bfe
commit 10146af099
2 changed files with 108 additions and 25 deletions
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docs/advanced_features/attention_backend.md
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@@ -15,34 +15,34 @@ The support matrix is split into two parts: MHA (standard attention) and MLA (mu
### MHA Backends
| **Backend** | **Page Size > 1 (native)** | **FP8 KV Cache** | **Spec topk=1** | **Spec topk>1** | **Sliding Window** | **MultiModal** |
|---------------------------------|-----------------------------|------------------|-----------------|-----------------|--------------------|----------------|
| **FlashInfer** | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ |
| **FA3 (FlashAttention 3)** | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| **FA4 (FlashAttention 4)** | 128 | ❌ | ❌ | ❌ | ❌ | ❌ |
| **Triton** | ❌ | ❌ | ✅ | ✅ | ✅ | ✅ |
| **Torch Native (SDPA)** | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ |
| **FlexAttention (PyTorch)** | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **TRTLLM MHA** | 16, 32 or 64 | ✅ | ✅ | ❌ | ✅ | ❌ |
| **Dual Chunk FlashAttention** | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **AITER (ROCm)** | ✅ | ❌ | ✅ | ✅ | ❌ | ✅ |
| **Wave (ROCm)** | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **Ascend (NPU)** | ✅ | ❌ | ❌ | ❌ | ❌ | ✅ |
| **Intel XPU** | ✅ | ❌ | ❌ | ❌ | ✅ | ❌ |
| **Intel AMX (CPU)** | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **Backend** | **Page Size > 1 (native)** | **FP8 KV Cache** | **FP4 KV Cache** | **Spec topk=1** | **Spec topk>1** | **Sliding Window** | **MultiModal** |
|---------------------------------|-----------------------------|------------------|-----------------|-----------------|-----------------|--------------------|----------------|
| **FlashInfer** | ✅ | ✅ | ❌ | ✅ | ✅ | ✅ | ❌ |
| **FA3 (FlashAttention 3)** | ✅ | ✅ | ❌ | ✅ | ✅ | ✅ | ✅ |
| **FA4 (FlashAttention 4)** | 128 | ❌ | ✅ | ❌ | ❌ | ❌ | ❌ |
| **Triton** | ❌ | ❌ | ✅ | ✅ | ✅ | ✅ | ✅ |
| **Torch Native (SDPA)** | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ | ✅ |
| **FlexAttention (PyTorch)** | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ | ❌ |
| **TRTLLM MHA** | 16, 32 or 64 | ✅ | ✅ | ✅ | ❌ | ✅ | ❌ |
| **Dual Chunk FlashAttention** | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **AITER (ROCm)** | ✅ | ❌ | ❌ | ✅ | ✅ | ❌ | ✅ |
| **Wave (ROCm)** | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
| **Ascend (NPU)** | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ |
| **Intel XPU** | ✅ | ❌ | ❌ | ❌ | ❌ | ✅ | ❌ |
| **Intel AMX (CPU)** | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
### MLA Backends
| **Backend** | **Native Page Sizes** | **FP8 KV Cache** | **Chunked Prefix Cache** | **Spec topk=1** | **Spec topk>1** |
|----------------------------|---------------------------|------------------|--------------------------|-----------------|-----------------|
| **FlashInfer MLA** | 1 | ❌ | ✅ | ✅ | ❌ |
| **FlashMLA** | 64 | ✅ | ✅ | ✅ | ❌ |
| **Cutlass MLA** | 128 | ✅ | ✅ | ✅ | ❌ |
| **TRTLLM MLA (Blackwell)** | 32 or 64 | ✅ | ✅ | ✅ | ❌ |
| **FA3 (FlashAttention 3)** | n/a | ❌ | ✅ | ✅ | ⚠️ (page_size=1 only) |
| **Triton** | n/a | ❌ | ❌ | ✅ | ⚠️ (page_size=1 only) |
| **FA4** | 1 | ❌ | ❌ | ❌ | ❌ |
| **Ascend MLA (NPU)** | 128 | ❌ | ❌ | ❌ | ❌ |
| **Backend** | **Native Page Sizes** | **FP8 KV Cache** | **FP4 KV Cache** | **Chunked Prefix Cache** | **Spec topk=1** | **Spec topk>1** |
|----------------------------|---------------------------|------------------|------------------|--------------------------|-----------------|-----------------|
| **FlashInfer MLA** | 1 | ❌ | ✅ | ✅ | ✅ | ❌ |
| **FlashMLA** | 64 | ✅ | ❌ | ✅ | ✅ | ❌ |
| **Cutlass MLA** | 128 | ✅ | ✅ | ✅ | ✅ | ❌ |
| **TRTLLM MLA (Blackwell)** | 32 or 64 | ✅ | ✅ | ✅ | ✅ | ❌ |
| **FA3 (FlashAttention 3)** | n/a | ❌ | ❌ | ✅ | ✅ | ⚠️ (page_size=1 only) |
| **Triton** | n/a | ❌ | ❌ | ❌ | ✅ | ⚠️ (page_size=1 only) |
| **FA4** | 1 | ❌ | ✅ | ❌ | ❌ | ❌ |
| **Ascend MLA (NPU)** | 128 | ❌ | ❌ | ❌ | ❌ | ❌ |
```{note}
Multimodal attention is selected by `--mm-attention-backend`. The "MultiModal" column indicates whether a corresponding multimodal implementation exists for that backend family.
@@ -53,6 +53,10 @@ Multimodal attention is selected by `--mm-attention-backend`. The "MultiModal" c
- NSA is specifically designed for [DeepSeek V3.2 DSA](https://lmsys.org/blog/2025-09-29-deepseek-V32/).
```
```{note}
For the KV4 FA4 scenario, FA4 requires using a different --decode-attention-backend to run. Except for trtllm_mha being incompatible with FA4, all other decode backends behave as shown in the table.
```
```{tip}
Speculative decoding topk: `topk` is the number of draft tokens sampled per step from the draft model. `topk = 1` follows classic EAGLE; `topk > 1` explores multiple branches and requires backend support in both draft and verification paths.
```