[Spec Decode] Move ops.advance_step to flash attn advance_step (#8224)

vllm/attention/backends/flash_attn.py

@@ -16,7 +16,8 @@ from vllm.attention.backends.utils import (PAD_SLOT_ID, CommonAttentionState,
 from vllm.utils import async_tensor_h2d, make_tensor_with_pad
 
 if TYPE_CHECKING:
-    from vllm.worker.model_runner import ModelInputForGPUBuilder
+    from vllm.worker.model_runner import (ModelInputForGPUBuilder,
+                                          ModelInputForGPUWithSamplingMetadata)
 
 from vllm_flash_attn import flash_attn_varlen_func as _flash_attn_varlen_func
 from vllm_flash_attn import flash_attn_with_kvcache as _flash_attn_with_kvcache
@@ -302,14 +303,12 @@ class FlashAttentionMetadata(AttentionMetadata):
         )
         return self._cached_decode_metadata
 
-    def advance_step(self, num_seqs: int, num_queries: int):
+    def advance_step(self, model_input: "ModelInputForGPUWithSamplingMetadata",
+                     sampled_token_ids: Optional[torch.Tensor],
+                     block_size: int, num_seqs: int, num_queries: int):
         """
         Update metadata in-place to advance one decode step.
         """
-        # GPU in-place update is currently called separately through
-        # custom_ops.advance_step(). See draft_model_runner. TODO(will): Move
-        # this logic to the backend.
-
         # When using cudagraph, the num_seqs is padded to the next captured
         # batch sized, but num_queries tracks the actual number of requests in
         # the batch. For --enforce-eager mode, num_seqs == num_queries
@@ -347,6 +346,16 @@ class FlashAttentionMetadata(AttentionMetadata):
             self.seq_lens[i] += 1
         self.max_decode_seq_len = max(self.seq_lens)
 
+        ops.advance_step(num_seqs=num_seqs,
+                         num_queries=num_queries,
+                         block_size=block_size,
+                         input_tokens=model_input.input_tokens,
+                         sampled_token_ids=sampled_token_ids,
+                         input_positions=model_input.input_positions,
+                         seq_lens=self.seq_lens_tensor,
+                         slot_mapping=self.slot_mapping,
+                         block_tables=self.block_tables)
+
 
 class FlashAttentionMetadataBuilder(
         AttentionMetadataBuilder[FlashAttentionMetadata]):

vllm/spec_decode/draft_model_runner.py

@@ -2,7 +2,6 @@ from typing import List, Optional
 
 import torch
 
-from vllm import _custom_ops as ops
 from vllm.model_executor.layers.sampler import SamplerOutput
 
 try:
@@ -116,18 +115,9 @@ class TP1DraftModelRunner(ModelRunner):
         # Update attn_metadata
         attn_metadata = model_input.attn_metadata
         assert isinstance(attn_metadata, FlashAttentionMetadata)
-        attn_metadata.advance_step(num_seqs, num_queries)
-
-        # Update GPU tensors
-        ops.advance_step(num_seqs=num_seqs,
-                         num_queries=num_queries,
-                         block_size=self.block_size,
-                         input_tokens=model_input.input_tokens,
-                         sampled_token_ids=sampled_token_ids,
-                         input_positions=model_input.input_positions,
-                         seq_lens=attn_metadata.seq_lens_tensor,
-                         slot_mapping=attn_metadata.slot_mapping,
-                         block_tables=attn_metadata.block_tables)
+
+        attn_metadata.advance_step(model_input, sampled_token_ids,
+                                   self.block_size, num_seqs, num_queries)
 
         # Update sampling_metadata
         sampling_metadata = model_input.sampling_metadata

vllm/worker/multi_step_model_runner.py

@@ -13,7 +13,6 @@ except ModuleNotFoundError:
 
 import torch
 
-from vllm import _custom_ops as ops
 from vllm.distributed import get_pp_group
 from vllm.logger import init_logger
 from vllm.model_executor.layers.sampler import (PromptLogprobs, SampleLogprobs,
@@ -499,19 +498,11 @@ class MultiStepModelRunner(GPUModelRunnerBase[StatefulModelInput]):
 
         attn_metadata = frozen_model_input.attn_metadata
         assert isinstance(attn_metadata, FlashAttentionMetadata)
-        attn_metadata.advance_step(num_seqs, num_queries)
-
-        # Update GPU tensors
-        ops.advance_step(
-            num_seqs=num_seqs,
-            num_queries=num_queries,
-            block_size=self.block_size,
-            input_tokens=frozen_model_input.input_tokens,
-            sampled_token_ids=model_input.cached_outputs[-1].sampled_token_ids,
-            input_positions=frozen_model_input.input_positions,
-            seq_lens=attn_metadata.seq_lens_tensor,
-            slot_mapping=attn_metadata.slot_mapping,
-            block_tables=attn_metadata.block_tables)
+
+        attn_metadata.advance_step(
+            frozen_model_input,
+            model_input.cached_outputs[-1].sampled_token_ids, self.block_size,
+            num_seqs, num_queries)
 
         if frozen_model_input.seq_lens is not None:
             for i in range(num_queries):