[Bugfix] handle prompt_logprobs in _apply_min_tokens_penalty (#3876)

Signed-off-by: Travis Johnson <tsjohnso@us.ibm.com>

tests/samplers/test_sampler.py

+import itertools
 import random
 from typing import List, Optional, Tuple
 from unittest.mock import patch
@@ -194,11 +195,15 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
 
     def create_sampling_params(min_tokens,
                                eos_token_id=0,
-                               stop_token_ids=None):
+                               *,
+                               stop_token_ids: Optional[List[str]] = None,
+                               prompt_logprobs: Optional[int] = None):
         sampling_params = SamplingParams(
             min_tokens=min_tokens,
             max_tokens=9999,  # keep higher than max of min_tokens
             stop_token_ids=stop_token_ids,
+            # requesting prompt_logprobs changes the structure of `logits`
+            prompt_logprobs=prompt_logprobs,
         )
         sampling_params.eos_token_id = eos_token_id
         return sampling_params
@@ -217,9 +222,9 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
 
         expected_penalization = []
         sequence_metadata_list = []
+        # 20% chance to generate seq group metadata list with all prompts
+        is_prompt = random.random() < 0.2
         while batch_size > 0:
-            # 20% chance to generate prompt seq group with single sequence
-            is_prompt = random.random() < 0.2
             num_seqs = 1 if is_prompt else random.randint(1, batch_size)
 
             eos_token_id = random.randint(0, VOCAB_SIZE - 1)
@@ -240,7 +245,7 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
             seq_group_penalization = []
             for _ in range(num_seqs):
                 num_input = random.randint(1, 100)
-                num_generated = random.randint(1, 100) if not is_prompt else 0
+                num_generated = 0 if is_prompt else random.randint(1, 100)
                 seq_data[next(seq_id_counter)] = create_sequence_data(
                     num_input=num_input, num_generated=num_generated)
                 seq_group_penalization.append(num_generated < min_tokens)
@@ -292,6 +297,21 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
         ]
     }
 
+    prompt_with_penalization_and_prompt_logprobs = {
+        "expected_penalization": [False, False, True],
+        "seq_group_metadata_list": [
+            SequenceGroupMetadata(
+                request_id="test_1",
+                is_prompt=True,
+                seq_data={
+                    next(seq_id_counter): create_sequence_data(num_input=3),
+                },
+                sampling_params=create_sampling_params(1, prompt_logprobs=3),
+                block_tables={},
+            ),
+        ]
+    }
+
     stop_penalizing_after_min_tokens = {
         "expected_penalization": [False],
         "seq_group_metadata_list": [
@@ -309,8 +329,34 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
     }
 
     stop_token_ids = [42, 99, 42, 0]  # intentional duplication
-    simple_combination = {
-        "expected_penalization": [True, False, False],
+    prompt_combination = {
+        "expected_penalization": [False, True, False],
+        "seq_group_metadata_list": [
+            SequenceGroupMetadata(
+                request_id="test_2",
+                is_prompt=True,
+                seq_data={
+                    next(seq_id_counter): create_sequence_data(num_input=2),
+                },
+                sampling_params=create_sampling_params(1, prompt_logprobs=3),
+                block_tables={},
+            ),
+            SequenceGroupMetadata(
+                request_id="test_3",
+                is_prompt=True,
+                seq_data={
+                    next(seq_id_counter): create_sequence_data(),
+                },
+                sampling_params=create_sampling_params(
+                    0, stop_token_ids=stop_token_ids),
+                block_tables={},
+            )
+        ]
+    }
+
+    stop_token_ids = [1, 999, 37, 37]  # intentional duplication
+    decode_combination = {
+        "expected_penalization": [True, False, False, True, False],
         "seq_group_metadata_list": [
             SequenceGroupMetadata(
                 request_id="test_1",
@@ -327,14 +373,19 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
             ),
             SequenceGroupMetadata(
                 request_id="test_2",
-                is_prompt=True,
+                is_prompt=False,
                 seq_data={
-                    next(seq_id_counter): create_sequence_data(),
+                    next(seq_id_counter):
+                    create_sequence_data(num_generated=20),
+                    next(seq_id_counter):
+                    create_sequence_data(num_generated=1),
+                    next(seq_id_counter):
+                    create_sequence_data(num_generated=10),
                 },
                 sampling_params=create_sampling_params(
-                    0, stop_token_ids=stop_token_ids),
+                    10, prompt_logprobs=5, stop_token_ids=stop_token_ids),
                 block_tables={},
-            )
+            ),
         ]
     }
 
@@ -342,8 +393,10 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
         test_cases = [
             prompt_without_penalization,
             prompt_with_penalization,
+            prompt_with_penalization_and_prompt_logprobs,
             stop_penalizing_after_min_tokens,
-            simple_combination,
+            prompt_combination,
+            decode_combination,
         ]
     else:
         test_cases = [generate_test_case()]
@@ -351,30 +404,49 @@ def test_sampler_min_tokens_penalty(seed: int, device: str):
     def run_test_case(*,
                       expected_penalization=None,
                       seq_group_metadata_list=None):
-        assert expected_penalization, "Invalid test case"
-        assert seq_group_metadata_list, "Invalid test case"
+        assert expected_penalization, \
+            "Invalid test case, need expected_penalization"
+        assert seq_group_metadata_list, \
+            "Invalid test case, need seq_group_metadata_list"
 
         batch_size = 0
         prompt_lens = []
-        sampling_params_per_seq = []
+        sampling_params_per_row = []
         for sgm in seq_group_metadata_list:
-            num_seqs = len(sgm.seq_data)
-            batch_size += num_seqs
             sampling_params = sgm.sampling_params
-            for seq_id in sgm.seq_data:
-                prompt_lens.append(sgm.seq_data[seq_id].get_prompt_len())
-                sampling_params_per_seq.append(sampling_params)
+
+            num_rows = len(sgm.seq_data)
+            if sgm.is_prompt:
+                # a prompt seq_group has only one sequence
+                seq_data = next(iter(sgm.seq_data.values()))
+                prompt_len = seq_data.get_prompt_len()
+                prompt_lens.append(prompt_len)
+
+                if sgm.sampling_params.prompt_logprobs:
+                    # with prompt_logprobs each token in the prompt has a row in
+                    # logits
+                    num_rows = prompt_len
+
+            batch_size += num_rows
+            sampling_params_per_row.extend(
+                itertools.repeat(sampling_params, num_rows))
+
+        assert len(
+            expected_penalization
+        ) == batch_size, \
+            ("Invalid test case, expected_penalization does not match computed"
+             "batch size")
 
         _, fake_logits, sampler, model_runner = _prepare_test(batch_size)
         sampling_metadata = model_runner._prepare_sample(
             seq_group_metadata_list,
-            prompt_lens=prompt_lens,
-            subquery_lens=prompt_lens)
+            prompt_lens=prompt_lens if prompt_lens else None,
+            subquery_lens=prompt_lens if prompt_lens else None)
         # the logits tensor is modified in-place by the sampler
         _ = sampler(logits=fake_logits, sampling_metadata=sampling_metadata)
 
         for logits_idx, (should_penalize, sampling_params) in enumerate(
-                zip(expected_penalization, sampling_params_per_seq)):
+                zip(expected_penalization, sampling_params_per_row)):
 
             tokens_to_check = [sampling_params.eos_token_id]
             if sampling_params.stop_token_ids:

vllm/model_executor/layers/sampler.py

@@ -27,6 +27,12 @@ class Sampler(nn.Module):
     6. Sample the next tokens.
     Here, each sequence group within the batch can have different sampling
     parameters (e.g., sampling method, temperature, top-p, top-k, etc.).
+
+    The structure of the logits tensor is coupled with the seq_groups in
+    sampling_metadata. Typically, each sequence in each seq_group has one row in
+    logits for the next token to be sampled; however, for a seq_group with a
+    prompt request with the prompt_logprobs sampling parameter, there are rows
+    in logits for each token in the input prompt.
     """
 
     def forward(
@@ -106,7 +112,16 @@ def _apply_min_tokens_penalty(
     # list of indices in logits that will be set to -inf
     logits_to_penalize = []
     start_idx = 0
-    for seq_ids, sampling_params in sampling_metadata.seq_groups:
+    for i, seq_group in enumerate(sampling_metadata.seq_groups):
+        seq_ids, sampling_params = seq_group
+
+        # handle prompt_logprobs by skipping rows in logits added for the prompt
+        # tokens (prompt logprobs are not penalized)
+        if (i < sampling_metadata.num_prompts
+                and sampling_params.prompt_logprobs is not None):
+            assert len(seq_ids) == 1
+            start_idx += sampling_metadata.prompt_lens[i] - 1
+
         min_tokens = sampling_params.min_tokens
         if min_tokens > 0:
             seqs_to_penalize = []
@@ -132,6 +147,8 @@ def _apply_min_tokens_penalty(
         # eg. [ (1,2), (1,3), (5,6) ] -> ( (1,1,5), (2,3,6) )
         logits[tuple(zip(*logits_to_penalize))] = -float("inf")
 
+    # verifies that no rows in logits were missed unexpectedly
+    assert start_idx == logits.shape[0]
     return logits