[Misc] Avoid accessing req_ids inside a loop (#23159)

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

vllm/v1/worker/gpu_model_runner.py

@@ -1748,6 +1748,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         # NOTE(woosuk): As an exception, when using PP, the scheduler sends
         # the sampled tokens back, because there's no direct communication
         # between the first-stage worker and the last-stage worker.
+        req_ids = self.input_batch.req_ids
         for req_idx, sampled_ids in enumerate(valid_sampled_token_ids):
             if not sampled_ids:
                 continue
@@ -1763,7 +1764,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                                            start_idx:end_idx] = sampled_ids
             self.input_batch.num_tokens_no_spec[req_idx] = end_idx
             self.input_batch.num_tokens[req_idx] = end_idx
-            req_id = self.input_batch.req_ids[req_idx]
+            req_id = req_ids[req_idx]
             req_state = self.requests[req_id]
             req_state.output_token_ids.extend(sampled_ids)
 
@@ -1843,6 +1844,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         elif self.speculative_config.use_eagle():
             assert isinstance(self.drafter, EagleProposer)
             # TODO(woosuk): Refactor the loop.
+            req_ids = self.input_batch.req_ids
             next_token_ids: list[int] = []
             for i, token_ids in enumerate(sampled_token_ids):
                 if token_ids:
@@ -1851,7 +1853,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 else:
                     # Partial prefill (rare case).
                     # Get the next token id from the request state.
-                    req_id = self.input_batch.req_ids[i]
+                    req_id = req_ids[i]
                     req_state = self.requests[req_id]
                     seq_len = (req_state.num_computed_tokens +
                                scheduler_output.num_scheduled_tokens[req_id])
@@ -1914,6 +1916,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         sampled_token_ids: list[list[int]],
     ) -> list[list[int]]:
         # TODO(woosuk): Optimize.
+        req_ids = self.input_batch.req_ids
         draft_token_ids: list[list[int]] = []
         for i, sampled_ids in enumerate(sampled_token_ids):
             num_sampled_ids = len(sampled_ids)
@@ -1924,7 +1927,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
 
             # Skip requests that require sampling parameters that are not
             # supported with speculative decoding.
-            req_id = self.input_batch.req_ids[i]
+            req_id = req_ids[i]
             if req_id in self.input_batch.spec_decode_unsupported_reqs:
                 draft_token_ids.append([])
                 continue