[Attention] FlashAttn MLA (#14258)

Signed-off-by: Lucas Wilkinson <lwilkinson@neuralmagic.com>
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Signed-off-by: Matthew Bonanni <mbonanni001@gmail.com>
Co-authored-by: Matthew Bonanni <mbonanni001@gmail.com>
Co-authored-by: Matthew Bonanni <mbonanni@redhat.com>

vllm/v1/attention/backends/short_conv_attn.py

@@ -58,8 +58,9 @@ class ShortConvAttentionMetadataBuilder(
         state_indices_tensor = common_attn_metadata.block_table_tensor[:, 0]
 
         num_decodes, num_prefills, num_decode_tokens, num_prefill_tokens = (
-            split_decodes_and_prefills(common_attn_metadata,
-                                       decode_threshold=1))
+            split_decodes_and_prefills(
+                common_attn_metadata,
+                decode_threshold=self.reorder_batch_threshold))
         has_initial_states = None
         if num_prefills > 0:
             #[batch,]
@@ -78,4 +79,4 @@ class ShortConvAttentionMetadataBuilder(
             has_initial_states=has_initial_states,
             state_indices_tensor=state_indices_tensor,
         )
-        return attn_metadata
+        return attn_metadata
\ No newline at end of file

vllm/v1/attention/backends/xformers.py

@@ -3,7 +3,7 @@
 """Attention layer with XFormersAttention."""
 
 from dataclasses import dataclass
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, ClassVar, Optional
 
 import torch
 
@@ -197,6 +197,8 @@ class XFormersAttentionMetadata:
 class XFormersAttentionMetadataBuilder(
         AttentionMetadataBuilder[XFormersAttentionMetadata]):
 
+    reorder_batch_threshold: ClassVar[int] = 1
+
     def __init__(
         self,
         kv_cache_spec: AttentionSpec,
@@ -212,9 +214,10 @@ class XFormersAttentionMetadataBuilder(
 
     def reorder_batch(self, input_batch: "InputBatch",
                       scheduler_output: "SchedulerOutput") -> bool:
-        return reorder_batch_to_split_decodes_and_prefills(input_batch,
-                                                           scheduler_output,
-                                                           decode_threshold=1)
+        return reorder_batch_to_split_decodes_and_prefills(
+            input_batch,
+            scheduler_output,
+            decode_threshold=self.reorder_batch_threshold)
 
     def build(
         self,
@@ -223,8 +226,9 @@ class XFormersAttentionMetadataBuilder(
         fast_build: bool = False,
     ) -> XFormersAttentionMetadata:
         num_decodes, num_prefills, num_decode_tokens, num_prefill_tokens = (
-            split_decodes_and_prefills(common_attn_metadata,
-                                       decode_threshold=1))
+            split_decodes_and_prefills(
+                common_attn_metadata,
+                decode_threshold=self.reorder_batch_threshold))
 
         num_actual_tokens = common_attn_metadata.num_actual_tokens
         q_start_loc = common_attn_metadata.query_start_loc