[V1] Aggregate chunked prompt logprobs in model runner (#14875)

Signed-off-by: Nick Hill <nhill@redhat.com>

vllm/v1/engine/logprobs.py

@@ -115,7 +115,6 @@ class LogprobsProcessor:
         num_prompt_tokens, num_logprobs = logprobs.shape
 
         # Pythonize the torch tensors.
-        # TODO(rob): experiment with doing this in EngineCore?
         prompt_token_ranks = ranks.tolist()
         prompt_logprobs = logprobs.tolist()
         token_ids = token_ids.tolist()

vllm/v1/engine/output_processor.py

@@ -105,9 +105,7 @@ class RequestState:
         finished = finish_reason is not None
         final_only = self.output_kind == RequestOutputKind.FINAL_ONLY
 
-        # In follow up, we will switch to invariant where EngineCore
-        # does not stream partial prefills.
-        if not finished and (self.is_prefilling or final_only):
+        if not finished and final_only:
             # Only the final output is required in FINAL_ONLY mode.
             return None
 
@@ -285,19 +283,7 @@ class OutputProcessor:
             finish_reason = engine_core_output.finish_reason
             stop_reason = engine_core_output.stop_reason
 
-            # TODO(andy): prompt logprobs + chunked prefill can
-            # result in engine core returning an output for a
-            # partial prefill (in order to send back partial
-            # prompt logprobs.) This breaks the invariant that
-            # process_outputs is only operating on engine core
-            # outputs associated with non-partial completions.
-            # Currently this is handled by having `is_prefilling`
-            # check for new decoded tokens, indicating that
-            # the completion is not partial.
-            #
-            # Follow up will aggregate partial prompt logprobs
-            # in the EngineCore.
-            req_state.is_prefilling = not new_token_ids
+            req_state.is_prefilling = False
 
             # 2) Detokenize the token ids into text and perform stop checks.
             stop_string = req_state.detokenizer.update(
@@ -306,8 +292,7 @@ class OutputProcessor:
                 finish_reason = FinishReason.STOP
                 stop_reason = stop_string
 
-            # 3) Compute sample and prompt logprobs for request,
-            #    if required.
+            # 3) Compute sample and prompt logprobs for request, if required.
             req_state.logprobs_processor.update_from_output(engine_core_output)
 
             # 4) Create and handle RequestOutput objects.