Add FA Unified Attention 2D

- Add VLLM_V1_USE_FA_UNIFIED_ATTN_2D 环境变量
- 0: Triton attention, 1: FA unified attention

vllm/envs.py

@@ -310,6 +310,7 @@ if TYPE_CHECKING:
     VLLM_USE_LIGHTOP_RMS_ROPE_CONCAT: bool = False
     VLLM_USE_CUDA_GRAPH_SIZES: bool = False
     VLLM_USE_LIGHTOP_FUSED_TOPP_TOPK: bool = False
+    VLLM_V1_USE_FA_UNIFIED_ATTN_2D: bool = False
 
 
 def get_default_cache_root():
@@ -1940,6 +1941,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_USE_LIGHTOP_FUSED_TOPP_TOPK":
         lambda: (os.environ.get("VLLM_USE_LIGHTOP_FUSED_TOPP_TOPK", "False").lower() in
                     ("true", "1")),
+    #If set to 1/True, enable the flash attention unified path.
+    "VLLM_V1_USE_FA_UNIFIED_ATTN_2D":
+        lambda: (os.environ.get("VLLM_V1_USE_FA_UNIFIED_ATTN_2D", "False").lower() in
+                    ("true", "1")),
 }
 
 # --8<-- [end:env-vars-definition]

vllm/model_executor/models/config.py

@@ -426,7 +426,7 @@ class HybridAttentionMambaModelConfig(VerifyAndUpdateConfig):
                 dtype=kv_cache_dtype,
             ).page_size_bytes
         else:
-            kernel_block_alignment_size = 16
+            kernel_block_alignment_size = 64
             if (
                 current_platform.is_device_capability_family(100)
                 and model_config.get_head_size() == 256

vllm/v1/attention/ops/triton_unified_attention.py

@@ -12,6 +12,10 @@ import torch
 from vllm.logger import init_logger
 from vllm.platforms import current_platform
 from vllm.triton_utils import tl, triton
+from vllm import envs
+from flash_attn import (
+    varlen_fwd_unified,
+)
 
 logger = init_logger(__name__)
 float8_info = torch.finfo(current_platform.fp8_dtype())
@@ -982,6 +986,9 @@ def unified_attention(
         or max_seqlen_q > 1
         or num_seqs > seq_threshold_3D
     ):
+        # print(f"[2D Triton] k shape: {k.shape}, v shape: {v.shape}")
+        if not envs.VLLM_V1_USE_FA_UNIFIED_ATTN_2D:
+            # print("Running Triton kernel")
             kernel_unified_attention_2d[
                 (
                     total_num_q_blocks,
@@ -1038,6 +1045,30 @@ def unified_attention(
                 USE_FP8=output_scale is not None,
             )
         else:
+            # print("Running FA kernel")
+            varlen_fwd_unified(
+                q=q,
+                k=k,
+                v=v,
+                cu_seqlens_q=cu_seqlens_q,
+                seqused_k=seqused_k,
+                block_table=block_table,
+                max_seqlen_q=max_seqlen_q,
+                max_seqlen_k=max_seqlen_k,
+                softmax_scale=softmax_scale,
+                causal=causal,
+                softcap=softcap,
+                window_size=window_size,
+                alibi_slopes=alibi_slopes,
+                use_alibi_sqrt=use_alibi_sqrt,
+                qq_bias=qq_bias,
+                s_aux=sinks,
+                mm_prefix_range=mm_prefix_range,
+                return_softmax_lse=False,
+                out=out,
+            )
+    else:
+        # print(f"[3D Triton] k shape: {k.shape}, v shape: {v.shape}")
         kernel_unified_attention_3d[
             (total_num_q_blocks, num_kv_heads, num_par_softmax_segments)
         ](