[Sampler] Introduce logprobs mode for logging (#21398)

Signed-off-by: Lu Fang <lufang@fb.com>

tests/v1/sample/test_logprobs.py

@@ -12,6 +12,7 @@ from tests.v1.sample.utils import (
     assert_incr_detok_str_matches_non_incr_detok_str,
     compute_correct_cumulative_logprob, get_test_batch)
 from vllm import SamplingParams
+from vllm.config import LogprobsMode
 
 from ...conftest import HfRunner, VllmRunner
 
@@ -426,3 +427,45 @@ def test_zero_logprobs(vllm_model, example_prompts,
             # prompt token
             assert prompt_logprobs is not None
             assert len(prompt_token_ids) == len(prompt_logprobs)
+
+
+@pytest.mark.parametrize(
+    "logprobs_mode",
+    ["raw_logprobs", "raw_logits", "processed_logprobs", "processed_logits"])
+def test_logprobs_mode(logprobs_mode: LogprobsMode,
+                       monkeypatch: pytest.MonkeyPatch):
+    """Test with LLM engine with different logprobs_mode.
+    For logprobs, we should have non-positive values.
+    For logits, we should expect at least one positive values.
+    """
+    from vllm import LLM
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_USE_V1", "1")
+
+        llm = LLM(
+            "facebook/opt-125m",
+            max_logprobs=5,
+            enable_prefix_caching=False,
+            # 2 other llms alive during whole session
+            gpu_memory_utilization=0.05,
+            max_model_len=16,
+            logprobs_mode=logprobs_mode)
+        vllm_sampling_params = SamplingParams(logprobs=1)
+        results = llm.generate(["Hello world"],
+                               sampling_params=vllm_sampling_params)
+
+        total_token_with_logprobs = 0
+        positive_values = 0
+        for output in results[0].outputs:
+            for logprobs in output.logprobs:
+                for token_id in logprobs:
+                    logprob = logprobs[token_id]
+                    if "logprobs" in logprobs_mode:
+                        assert logprob.logprob <= 0
+                    if logprob.logprob > 0:
+                        positive_values = positive_values + 1
+                    total_token_with_logprobs = total_token_with_logprobs + 1
+        assert total_token_with_logprobs >= len(results[0].outputs)
+        if "logits" in logprobs_mode:
+            assert positive_values > 0
+        del llm