[None][feat] Return logprobs incrementally in torch backend (#8785)

Signed-off-by: Dong Cao <docao@nvidia.com>

tensorrt_llm/_torch/pyexecutor/llm_request.py

@@ -1,4 +1,4 @@
-from copy import deepcopy
+from copy import copy, deepcopy
 from dataclasses import dataclass
 from typing import Any, Dict, List, Optional, Union
 
@@ -327,7 +327,8 @@ class PyResult:
 
     @property
     def log_probs(self) -> list[TokenLogprobs] | None:
-        return self._log_probs and self._log_probs.log_probs
+        return self._log_probs and hasattr(
+            self._log_probs, 'log_probs') and self._log_probs.log_probs
 
     @property
     def cum_log_probs(self) -> list[float] | None:
@@ -589,10 +590,21 @@ class LlmRequest(tensorrt_llm.bindings.internal.batch_manager.LlmRequest):
         """
         result, is_final = super().create_serialized_result(
             use_fast_logits, mpi_world_rank)
+
+        # Performs a deep copy of py_result._log_probs to eliminate race conditions that may occur between IPC communication and the overriding of newly generated log_probs in streaming mode.
+        if self.streaming and self.py_result.log_probs and self.sampling_config.beam_width <= 1:
+            py_result = copy(self.py_result)
+            py_result._log_probs = deepcopy(self.py_result._log_probs)
+
+            for log_prob in self.py_result.log_probs:
+                log_prob.clear()
+        else:
+            py_result = self.py_result
+
         return LlmResponse(
             request_id=self.py_request_id
             if self.is_child else self.parent_request_id,
-            result=LlmResult(result, self.py_result, is_final),
+            result=LlmResult(result, py_result, is_final),
             client_id=self.py_client_id) if len(result) > 0 else None
 
     @property

tensorrt_llm/executor/result.py

@@ -272,6 +272,8 @@ class GenerationResultBase:
         self._done = False
         self.metrics_dict = {}
         self.trace_headers: Optional[dict[str, str]] = None
+        # torch backend will use trtllm sampler in beam search mode, but it does not support return logprobs incrementally
+        self.use_trtllm_sampler = sampling_params.use_beam_search and sampling_params.best_of > 1
 
         if ray_queue is not None:
             if has_event_loop():
@@ -378,20 +380,27 @@ class GenerationResultBase:
             # each streamed response_tensors.log_probs[src_idx]
             # contains a streamwise monotonically growing list of logprobs.
             # so we need to accumulate only the new ones unique to that particular streamed response
-            assert output._last_logprobs_len <= len(
-                response_tensors.log_probs[src_idx]
-            ), (f"_last_logprobs_len ({output._last_logprobs_len}) > log_probs length ("
-                f"{len(response_tensors.log_probs[src_idx])})")
-            output.logprobs += response_tensors.log_probs[src_idx][
-                output._last_logprobs_len:]
+            if self.use_trtllm_sampler:
+                assert output._last_logprobs_len <= len(
+                    response_tensors.log_probs[src_idx]
+                ), (f"_last_logprobs_len ({output._last_logprobs_len}) > log_probs length ("
+                    f"{len(response_tensors.log_probs[src_idx])})")
+                output.logprobs += response_tensors.log_probs[src_idx][
+                    output._last_logprobs_len:]
+            else:
+                output.logprobs += response_tensors.log_probs[src_idx]
+
             # overcome some WAR in the cpp executor
-            if finish_reasons[src_idx] != tllm.FinishReason.CANCELLED:
+            if finish_reasons[
+                    src_idx] != tllm.FinishReason.CANCELLED and self.use_trtllm_sampler:
                 # Check if logprobs is a list (not a dict or other structure)
                 if len(output.logprobs) > output.length:
                     # LlmResult holds a reference to LogProbStorage, which may be updated by the worker before the result is serialized.
                     # Therefore, we treat extra logprobs/logits as expected and only consume what's needed.
                     output.logprobs = output.logprobs[:output.length]
-                assert len(output.logprobs) == output.length
+            assert len(
+                output.logprobs
+            ) == output.length, f"logprobs length: {len(output.logprobs)} != output.length: {output.length}"
 
         if response_tensors.generation_logits is not None:
             output.generation_logits = response_tensors.generation_logits[