[Bugfix][SpecDecode] apply sampling parameters to target probabilities for consistency in rejection sampling.

tests/spec_decode/e2e/test_mlp_correctness.py

@@ -203,7 +203,7 @@ def test_mlp_e2e_acceptance_rate(vllm_runner, common_llm_kwargs,
 @pytest.mark.parametrize("test_llm_kwargs", [{"seed": 5}])
 @pytest.mark.parametrize("output_len", [64])
 @pytest.mark.parametrize("batch_size", [1, 32])
-@pytest.mark.parametrize("temperature", [0.1, 1.0])
+@pytest.mark.parametrize("temperature", [1.0])
 @pytest.mark.parametrize("seed", [1])
 def test_mlp_e2e_seeded_correctness(vllm_runner, common_llm_kwargs,
                                     per_test_common_llm_kwargs,

tests/spec_decode/test_batch_expansion.py

@@ -90,6 +90,14 @@ def test_create_single_target_seq_group_metadata(k: int):
     )
 
     assert output.request_id == input_seq_group_metadata.request_id
+    assert output.sampling_params.repetition_penalty == \
+        input_seq_group_metadata.sampling_params.repetition_penalty
+    assert output.sampling_params.temperature == \
+        input_seq_group_metadata.sampling_params.temperature
+    assert output.sampling_params.top_p == \
+        input_seq_group_metadata.sampling_params.top_p
+    assert output.sampling_params.top_k == \
+        input_seq_group_metadata.sampling_params.top_k
     assert len(output.seq_data) == 1
     assert output.seq_data[target_seq_id].get_prompt_token_ids() == tuple(
         prompt_tokens)

vllm/spec_decode/batch_expansion.py

@@ -307,28 +307,16 @@ def _create_target_seq_group_metadata(
         token_ids_to_score = self._get_token_ids_to_score(
             proposal_token_ids[batch_index])
 
-        # Use simpler sampling parameters apart from for final token
-        # (in particular don't do seeded sampling) since those sampled tokens
-        # aren't used.
-        # We don't replace the sampling_params in the greedy case because
-        # this also controls whether the probs get modified in the sampler
-        # (see use of _modify_greedy_probs_inplace there).
         sampling_params = input_seq_group_metadata.sampling_params
-        non_bonus_sampling_params = DEFAULT_SIMPLE_SAMPLING_PARAMS \
-            if sampling_params.temperature else sampling_params
-
         target_seq_group_metadata_list: List[SequenceGroupMetadata] = []
-        last_index = len(token_ids_to_score) - 1
         for i, token_ids in enumerate(token_ids_to_score):
-            target_sampling_params = sampling_params if i == last_index \
-                else non_bonus_sampling_params
             target_seq_group_metadata_list.append(
                 self._create_single_target_seq_group_metadata(
                     input_seq_group_metadata,
                     input_seq_id,
                     next(target_seq_ids_iter),
                     token_ids,
-                    sampling_params=target_sampling_params,
+                    sampling_params=sampling_params,
                 ))
 
         return target_seq_group_metadata_list