[Model Runner V2] Refactor get_cudagraph_and_dp_padding (#32625)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

vllm/v1/worker/gpu/dp_utils.py

@@ -6,6 +6,12 @@ import torch.distributed as dist
 from vllm.distributed.parallel_state import get_dp_group
 
 
+def make_num_tokens_across_dp(dp_size: int, num_tokens: int) -> torch.Tensor | None:
+    if dp_size == 1:
+        return None
+    return torch.full((dp_size,), num_tokens, dtype=torch.int32, device="cpu")
+
+
 def get_batch_metadata_across_dp(
     num_tokens: int,
     cudagraph_size: int,
@@ -22,10 +28,39 @@ def get_batch_metadata_across_dp(
     return tensor[0], tensor[1]
 
 
-def make_num_tokens_across_dp(
-    dp_size: int,
+def get_cudagraph_and_dp_padding(
     num_tokens: int,
-) -> torch.Tensor | None:
+    cudagraph_size: int | None,
+    dp_size: int,
+    dp_rank: int,
+) -> tuple[bool, int, torch.Tensor | None]:
     if dp_size == 1:
-        return None
-    return torch.full((dp_size,), num_tokens, dtype=torch.int32, device="cpu")
+        if cudagraph_size is not None:
+            return True, cudagraph_size, None
+        else:
+            return False, num_tokens, None
+
+    if num_tokens == 0:
+        cudagraph_size = 0
+    elif cudagraph_size is None:
+        cudagraph_size = -1
+    num_tokens_across_dp, cudagraph_size_across_dp = get_batch_metadata_across_dp(
+        num_tokens, cudagraph_size, dp_size, dp_rank
+    )
+    if torch.all(num_tokens_across_dp == 0).item():
+        # All ranks have zero tokens to run.
+        return False, 0, None
+
+    if torch.all(cudagraph_size_across_dp != -1).item():
+        # All ranks use CUDA graph or have zero tokens.
+        # Use CUDA graph for all ranks.
+        # Pad all ranks to the maximum CUDA graph size.
+        max_cudagraph_size = int(cudagraph_size_across_dp.max().item())
+        num_tokens_across_dp[:] = max_cudagraph_size
+        return True, max_cudagraph_size, num_tokens_across_dp
+    else:
+        # Some ranks do not use CUDA graph. Use eager mode for all ranks.
+        # No padding is needed except for ranks that have no tokens to run.
+        num_tokens_across_dp = torch.clamp(num_tokens_across_dp, min=1)
+        num_tokens_after_padding = int(num_tokens_across_dp[dp_rank].item())
+        return False, num_tokens_after_padding, num_tokens_across_dp

vllm/v1/worker/gpu/model_runner.py

@@ -2,7 +2,6 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import gc
 import time
-from collections.abc import Iterable
 from copy import deepcopy
 from typing import Any
 
@@ -37,7 +36,7 @@ from vllm.v1.worker.gpu.block_table import BlockTables
 from vllm.v1.worker.gpu.buffer_utils import UvaBufferPool
 from vllm.v1.worker.gpu.cudagraph_utils import CudaGraphManager
 from vllm.v1.worker.gpu.dp_utils import (
-    get_batch_metadata_across_dp,
+    get_cudagraph_and_dp_padding,
     make_num_tokens_across_dp,
 )
 from vllm.v1.worker.gpu.input_batch import (
@@ -877,60 +876,6 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         )
         return draft_tokens
 
-    def get_cudagraph_and_dp_padding(
-        self,
-        total_num_scheduled_tokens: int,
-        num_tokens_per_request: Iterable[int],
-    ) -> tuple[CUDAGraphMode, int, torch.Tensor | None]:
-        dp_size = self.parallel_config.data_parallel_size
-        if dp_size == 1:
-            # No DP. Only consider CUDA graphs.
-            if total_num_scheduled_tokens == 0:
-                # Special case: no tokens to run.
-                return CUDAGraphMode.NONE, 0, None
-
-            cudagraph_size = self.cudagraph_manager.get_cudagraph_size(
-                total_num_scheduled_tokens, num_tokens_per_request
-            )
-            if cudagraph_size is not None:
-                # Use full CUDA graph.
-                return CUDAGraphMode.FULL, cudagraph_size, None
-            # Fall back to eager mode.
-            # TODO(woosuk): Support piecewise CUDA graphs.
-            return CUDAGraphMode.NONE, total_num_scheduled_tokens, None
-
-        # Consider DP padding and CUDA graph.
-        if total_num_scheduled_tokens == 0:
-            # Special handling is needed for 0.
-            cudagraph_size_before_dp: int | None = 0
-        else:
-            cudagraph_size_before_dp = self.cudagraph_manager.get_cudagraph_size(
-                total_num_scheduled_tokens, num_tokens_per_request
-            )
-            if cudagraph_size_before_dp is None:
-                cudagraph_size_before_dp = -1
-
-        assert cudagraph_size_before_dp is not None
-        dp_rank = self.parallel_config.data_parallel_rank
-        num_tokens_across_dp, cudagraph_size_across_dp = get_batch_metadata_across_dp(
-            total_num_scheduled_tokens,
-            cudagraph_size_before_dp,
-            dp_size,
-            dp_rank,
-        )
-        if all(cudagraph_size_across_dp >= 0):
-            # If all ranks can use CUDA graph, pad to the maximum number of tokens
-            # across DP and use CUDA graph.
-            num_tokens_after_padding = int(cudagraph_size_across_dp.max().item())
-            cudagraph_mode = CUDAGraphMode.FULL
-        else:
-            # If any of the ranks cannot use CUDA graph, use eager mode for all ranks.
-            # No padding is needed except for ranks that have no tokens to run.
-            num_tokens_across_dp = torch.clamp(num_tokens_across_dp, min=1)
-            num_tokens_after_padding = num_tokens_across_dp[dp_rank]
-            cudagraph_mode = CUDAGraphMode.NONE
-        return cudagraph_mode, num_tokens_after_padding, num_tokens_across_dp
-
     @torch.inference_mode()
     def execute_model(
         self,
@@ -951,10 +896,17 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 # No need to run the model.
                 return EMPTY_MODEL_RUNNER_OUTPUT
 
-        cudagraph_mode, num_tokens_after_padding, num_tokens_across_dp = (
-            self.get_cudagraph_and_dp_padding(
+        # Get the CUDA graph size. None means no CUDA graph is used.
+        cudagraph_size = self.cudagraph_manager.get_cudagraph_size(
+            scheduler_output.total_num_scheduled_tokens,
+            scheduler_output.num_scheduled_tokens.values(),
+        )
+        use_cudagraph, num_tokens_after_padding, num_tokens_across_dp = (
+            get_cudagraph_and_dp_padding(
                 scheduler_output.total_num_scheduled_tokens,
-                scheduler_output.num_scheduled_tokens.values(),
+                cudagraph_size,
+                self.parallel_config.data_parallel_size,
+                self.parallel_config.data_parallel_rank,
             )
         )
         if num_tokens_after_padding == 0:
@@ -1006,7 +958,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             # FIXME(woosuk): Fix warmup for LoRA.
 
         # Run model.
-        if cudagraph_mode == CUDAGraphMode.FULL:
+        if use_cudagraph:
             # Run CUDA graph.
             # NOTE(woosuk): Here, we don't need to pass the input tensors,
             # because they are already copied to the CUDA graph input buffers.
@@ -1015,7 +967,6 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             )
         else:
             # Run PyTorch model in eager mode.
-            # TODO(woosuk): Support piecewise CUDA graph.
             positions = input_batch.positions
             if self.uses_mrope:
                 assert input_batch.mrope_positions is not None
@@ -1024,7 +975,8 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 input_batch.attn_metadata,
                 self.vllm_config,
                 num_tokens=input_batch.num_tokens_after_padding,
-                cudagraph_runtime_mode=cudagraph_mode,
+                # TODO(woosuk): Support piecewise CUDA graph.
+                cudagraph_runtime_mode=CUDAGraphMode.NONE,
                 num_tokens_across_dp=num_tokens_across_dp,
             ):
                 hidden_states = self.model(