Support per-request seed (#2514)

tests/samplers/test_sampler.py

 import random
-from typing import Tuple
+from typing import Tuple, List
 from unittest.mock import patch
 
 import pytest
 import torch
 from transformers import GenerationConfig, GenerationMixin
+from typing import Optional
 
 from vllm.model_executor.layers.sampler import Sampler
 from vllm.model_executor.utils import set_random_seed
@@ -46,15 +47,13 @@ CUDA_DEVICES = [
 ]
 
 
-@pytest.mark.parametrize("seed", RANDOM_SEEDS)
-@pytest.mark.parametrize("device", CUDA_DEVICES)
-def test_sampler_all_greedy(seed: int, device: str):
-    set_random_seed(seed)
-    torch.set_default_device(device)
-    batch_size = random.randint(1, 256)
-    input_tensor, fake_logits, sampler, model_runner = _prepare_test(
-        batch_size)
-
+def _do_sample(
+    batch_size: int,
+    input_tensor: torch.Tensor,
+    sampler: MockLogitsSampler,
+    model_runner: ModelRunner,
+    sampling_params: SamplingParams,
+):
     seq_group_metadata_list = []
     prompt_lens = []
     for i in range(batch_size):
@@ -63,7 +62,7 @@ def test_sampler_all_greedy(seed: int, device: str):
                 request_id=f"test_{i}",
                 is_prompt=True,
                 seq_data={0: SequenceData([1, 2, 3])},
-                sampling_params=SamplingParams(temperature=0, ),
+                sampling_params=sampling_params,
                 block_tables={0: [1]},
             ))
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
@@ -71,9 +70,23 @@ def test_sampler_all_greedy(seed: int, device: str):
     sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
                                                      prompt_lens,
                                                      subquery_lens=prompt_lens)
-    sampler_output = sampler(embedding=None,
-                             hidden_states=input_tensor,
-                             sampling_metadata=sampling_metadata)
+    return sampler(embedding=None,
+                   hidden_states=input_tensor,
+                   sampling_metadata=sampling_metadata)
+
+
+@pytest.mark.parametrize("seed", RANDOM_SEEDS)
+@pytest.mark.parametrize("device", CUDA_DEVICES)
+def test_sampler_all_greedy(seed: int, device: str):
+    set_random_seed(seed)
+    torch.set_default_device(device)
+    batch_size = random.randint(1, 256)
+    input_tensor, fake_logits, sampler, model_runner = _prepare_test(
+        batch_size)
+
+    sampling_params = SamplingParams(temperature=0)
+    sampler_output = _do_sample(batch_size, input_tensor, sampler,
+                                model_runner, sampling_params)
     expected = torch.argmax(fake_logits, dim=-1)
     for i, sequence_output in enumerate(sampler_output):
         for nth_output in sequence_output.samples:
@@ -94,28 +107,40 @@ def test_sampler_all_random(seed: int, device: str):
     for i in range(batch_size):
         fake_logits[i, i] = 1e2
 
-    seq_group_metadata_list = []
-    prompt_lens = []
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        n=random.randint(1, 10),
+    )
+    sampler_output = _do_sample(batch_size, input_tensor, sampler,
+                                model_runner, sampling_params)
+
+    for i, sequence_output in enumerate(sampler_output):
+        for nth_output in sequence_output.samples:
+            assert nth_output.output_token == i
+
+    del model_runner
+
+
+@pytest.mark.parametrize("seed", RANDOM_SEEDS)
+@pytest.mark.parametrize("device", CUDA_DEVICES)
+def test_sampler_all_random_seed(seed: int, device: str):
+    set_random_seed(seed)
+    torch.set_default_device(device)
+    batch_size = random.randint(1, 256)
+    input_tensor, fake_logits, sampler, model_runner = _prepare_test(
+        batch_size)
+
     for i in range(batch_size):
-        seq_group_metadata_list.append(
-            SequenceGroupMetadata(
-                request_id=f"test_{i}",
-                is_prompt=True,
-                seq_data={0: SequenceData([1, 2, 3])},
-                sampling_params=SamplingParams(
-                    temperature=1.0,
-                    n=random.randint(1, 10),
-                ),
-                block_tables={0: [1]},
-            ))
-        prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
+        fake_logits[i, i] = 1e2
+
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        n=random.randint(1, 10),
+        seed=random.randint(0, 10000),
+    )
+    sampler_output = _do_sample(batch_size, input_tensor, sampler,
+                                model_runner, sampling_params)
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
-    sampler_output = sampler(embedding=None,
-                             hidden_states=input_tensor,
-                             sampling_metadata=sampling_metadata)
     for i, sequence_output in enumerate(sampler_output):
         for nth_output in sequence_output.samples:
             assert nth_output.output_token == i
@@ -123,6 +148,31 @@ def test_sampler_all_random(seed: int, device: str):
     del model_runner
 
 
+@pytest.mark.parametrize("seed", RANDOM_SEEDS)
+@pytest.mark.parametrize("device", CUDA_DEVICES)
+def test_sampler_all_random_seed_deterministic(seed: int, device: str):
+    set_random_seed(seed)
+    torch.set_default_device(device)
+    batch_size = random.randint(1, 256)
+    input_tensor, fake_logits, sampler, model_runner = _prepare_test(
+        batch_size)
+
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        n=random.randint(1, 10),
+        seed=random.randint(0, 10000),
+    )
+    first_sampler_output = _do_sample(batch_size, input_tensor, sampler,
+                                      model_runner, sampling_params)
+
+    second_sampler_output = _do_sample(batch_size, input_tensor, sampler,
+                                       model_runner, sampling_params)
+
+    assert first_sampler_output == second_sampler_output
+
+    del model_runner
+
+
 @pytest.mark.parametrize("seed", RANDOM_SEEDS)
 @pytest.mark.parametrize("device", CUDA_DEVICES)
 def test_sampler_all_beam(seed: int, device: str):
@@ -131,29 +181,13 @@ def test_sampler_all_beam(seed: int, device: str):
     batch_size = random.randint(1, 256)
     input_tensor, _, sampler, model_runner = _prepare_test(batch_size)
 
-    seq_group_metadata_list = []
-    prompt_lens = []
-    for i in range(batch_size):
-        seq_group_metadata_list.append(
-            SequenceGroupMetadata(
-                request_id=f"test_{i}",
-                is_prompt=True,
-                seq_data={0: SequenceData([1, 2, 3])},
-                sampling_params=SamplingParams(
-                    temperature=0,
-                    best_of=2,
-                    use_beam_search=True,
-                ),
-                block_tables={0: [1]},
-            ))
-        prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
-
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
-    sampler(embedding=None,
-            hidden_states=input_tensor,
-            sampling_metadata=sampling_metadata)
+    sampling_params = SamplingParams(
+        temperature=0,
+        best_of=2,
+        use_beam_search=True,
+    )
+    _do_sample(batch_size, input_tensor, sampler, model_runner,
+               sampling_params)
     # no assertion here as I am not sure how to determine whether
     # the outputs are expected - in other words, this just tests
     # whether there are no exceptions in the sampler
@@ -171,14 +205,15 @@ def test_sampler_mixed(seed: int, device: str):
         batch_size)
 
     seq_group_metadata_list = []
-    expected_tokens = []
+    expected_tokens: List[Optional[List[int]]] = []
     prompt_lens = []
     for i in range(batch_size):
-        n = 1
-        sampling_type = random.randint(0, 2)
+        expected: Optional[List[int]] = None
+        sampling_type = random.randint(0, 3)
         if sampling_type == 0:
             sampling_params = SamplingParams(temperature=0)
-        elif sampling_type == 1:
+            expected = [torch.argmax(fake_logits[i], dim=-1).item()]
+        elif sampling_type in (1, 2):
             n = random.randint(1, 10)
             sampling_params = SamplingParams(
                 temperature=random.random() + 0.1,
@@ -187,13 +222,17 @@ def test_sampler_mixed(seed: int, device: str):
                 n=n,
                 presence_penalty=random.randint(0, 1),
             )
+            if sampling_type == 2:
+                sampling_params.seed = random.randint(0, 10000)
+            else:
+                for idx in range(n):
+                    fake_logits[i, i + idx] = 1e2
+                expected = list(range(i, i + n))
         else:
             sampling_params = SamplingParams(temperature=0,
                                              use_beam_search=True,
                                              best_of=2)
-        for idx in range(n):
-            fake_logits[i, i + idx] = 1e2
-            expected_tokens.append(i + idx)
+        expected_tokens.append(expected)
         seq_group_metadata_list.append(
             SequenceGroupMetadata(
                 request_id=f"test_{i}",
@@ -204,17 +243,50 @@ def test_sampler_mixed(seed: int, device: str):
             ))
         prompt_lens.append(seq_group_metadata_list[-1].seq_data[0].get_len())
 
-    sampling_metadata = model_runner._prepare_sample(seq_group_metadata_list,
-                                                     prompt_lens,
-                                                     subquery_lens=prompt_lens)
-    sampler_output = sampler(embedding=None,
-                             hidden_states=input_tensor,
-                             sampling_metadata=sampling_metadata)
-    for i, sequence_output in enumerate(sampler_output):
-        if seq_group_metadata_list[i].sampling_params.use_beam_search:
-            continue
-        for nth_output in sequence_output.samples:
-            assert nth_output.output_token in expected_tokens
+    def test_sampling(model_runner: ModelRunner):
+        sampling_metadata = model_runner._prepare_sample(
+            seq_group_metadata_list, prompt_lens, subquery_lens=prompt_lens)
+        sampler_output = sampler(embedding=None,
+                                 hidden_states=input_tensor,
+                                 sampling_metadata=sampling_metadata)
+
+        for i, (sequence_output, metadata) in enumerate(
+                zip(sampler_output, seq_group_metadata_list)):
+            if metadata.sampling_params.use_beam_search:
+                continue
+
+            if metadata.sampling_params.seed is not None \
+                    and expected_tokens[i] is None:
+                # Record seeded random result to compare with results of second invocation
+                expected_tokens[i] = [
+                    nth_output.output_token
+                    for nth_output in sequence_output.samples
+                ]
+                continue
+
+            for n, nth_output in enumerate(sequence_output.samples):
+                if metadata.sampling_params.temperature == 0 or metadata.sampling_params.seed is not None:
+                    # Ensure exact matches for greedy or random with seed
+                    assert nth_output.output_token == expected_tokens[i][n]
+                else:
+                    # For non-seeded random check that one of the high-logit tokens were chosen
+                    assert nth_output.output_token in expected_tokens[i]
+
+    # Test batch
+    test_sampling(model_runner)
+
+    # Shuffle the batch and resample
+    target_index = list(range(batch_size))
+    for list_to_shuffle in (target_index, seq_group_metadata_list,
+                            expected_tokens, prompt_lens):
+        random.Random(seed).shuffle(list_to_shuffle)
+    target_index = torch.tensor(target_index)
+    input_tensor.data = input_tensor.index_select(0, target_index)
+    fake_logits.data = fake_logits.index_select(0, target_index)
+
+    # This time, results of seeded random samples will be compared with the corresponding
+    # sample in the pre-shuffled batch
+    test_sampling(model_runner)
 
     del model_runner
 

tests/samplers/test_seeded_generate.py

+"""Verify that seeded random sampling is deterministic.
+
+Run `pytest tests/samplers/test_seeded_generate.py --forked`.
+"""
+import copy
+import random
+from itertools import combinations
+
+import pytest
+
+from vllm.model_executor.utils import set_random_seed
+from vllm import SamplingParams
+
+MODEL = "facebook/opt-125m"
+RANDOM_SEEDS = list(range(5))
+
+
+@pytest.fixture
+def vllm_model(vllm_runner):
+    vllm_model = vllm_runner(MODEL, dtype="half")
+    yield vllm_model
+    del vllm_model
+
+
+@pytest.mark.parametrize("seed", RANDOM_SEEDS)
+def test_random_sample_with_seed(
+    vllm_model,
+    example_prompts,
+    seed: int,
+) -> None:
+    set_random_seed(seed)
+
+    sampling_params = SamplingParams(
+        # Parameters to ensure sufficient randomness
+        temperature=2.0,
+        top_p=min(random.random() + 0.3, 1),
+        top_k=random.randint(5, 20),
+        n=random.randint(1, 10),
+        presence_penalty=random.randint(0, 1),
+        max_tokens=8,
+        ignore_eos=True,
+    )
+
+    sampling_params_seed_1 = copy.deepcopy(sampling_params)
+    sampling_params_seed_1.seed = 100
+    sampling_params_seed_2 = copy.deepcopy(sampling_params)
+    sampling_params_seed_2.seed = 200
+
+    llm = vllm_model.model
+
+    for prompt in example_prompts:
+        for params in (
+                sampling_params,
+                sampling_params_seed_1,
+                sampling_params_seed_2,
+                sampling_params,
+                sampling_params_seed_1,
+                sampling_params_seed_2,
+        ):
+            llm._add_request(
+                prompt=prompt,
+                prompt_token_ids=None,
+                sampling_params=params,
+            )
+
+    results = llm._run_engine(use_tqdm=False)
+    all_outputs = [[out.token_ids for out in output.outputs]
+                   for output in results]
+
+    for i in range(0, len(example_prompts), 6):
+        outputs = all_outputs[i:i + 6]
+
+        # verify all non-seeded requests differ
+        for output_a, output_b in combinations(
+            (outputs[0], outputs[1], outputs[2], outputs[3]),
+                2,
+        ):
+            assert output_a != output_b
+
+        # verify requests with the same seed match
+        assert outputs[1] == outputs[4]
+        assert outputs[2] == outputs[5]

vllm/core/scheduler.py

@@ -387,6 +387,7 @@ class Scheduler:
                 block_tables=block_tables,
                 lora_request=seq_group.lora_request,
                 prefix=seq_group.prefix,
+                state=seq_group.state,
             )
             seq_group_metadata_list.append(seq_group_metadata)
         return seq_group_metadata_list, scheduler_outputs

vllm/engine/arg_utils.py

@@ -173,7 +173,6 @@ class EngineArgs:
                             default=EngineArgs.block_size,
                             choices=[8, 16, 32],
                             help='token block size')
-        # TODO(woosuk): Support fine-grained seeds (e.g., seed per request).
         parser.add_argument('--seed',
                             type=int,
                             default=EngineArgs.seed,

vllm/entrypoints/openai/protocol.py

@@ -60,6 +60,7 @@ class ChatCompletionRequest(BaseModel):
     top_p: Optional[float] = 1.0
     n: Optional[int] = 1
     max_tokens: Optional[int] = None
+    seed: Optional[int] = None
     stop: Optional[Union[str, List[str]]] = Field(default_factory=list)
     stream: Optional[bool] = False
     presence_penalty: Optional[float] = 0.0
@@ -90,6 +91,7 @@ class ChatCompletionRequest(BaseModel):
             temperature=self.temperature,
             top_p=self.top_p,
             min_p=self.min_p,
+            seed=self.seed,
             stop=self.stop,
             stop_token_ids=self.stop_token_ids,
             max_tokens=self.max_tokens,
@@ -117,6 +119,7 @@ class CompletionRequest(BaseModel):
     logprobs: Optional[int] = None
     echo: Optional[bool] = False
     stop: Optional[Union[str, List[str]]] = Field(default_factory=list)
+    seed: Optional[int] = None
     presence_penalty: Optional[float] = 0.0
     frequency_penalty: Optional[float] = 0.0
     best_of: Optional[int] = None
@@ -147,6 +150,7 @@ class CompletionRequest(BaseModel):
             top_p=self.top_p,
             top_k=self.top_k,
             min_p=self.min_p,
+            seed=self.seed,
             stop=self.stop,
             stop_token_ids=self.stop_token_ids,
             ignore_eos=self.ignore_eos,

vllm/model_executor/layers/sampler.py

@@ -342,7 +342,9 @@ def _beam_search_sample(
 def _multinomial(
     probs: torch.Tensor,
     num_samples: int,
-):
+    seq_groups: Optional[List[Tuple[List[int], SamplingParams]]] = None,
+    generators: Optional[List[torch.Generator]] = None,
+) -> torch.Tensor:
     if num_samples > 1:
         # This is equivalent to torch.repeat_interleaved (which also
         # forces a GPU<->CPU sync).
@@ -352,7 +354,15 @@ def _multinomial(
         probs = probs[:, None, :].expand(probs.shape[0], num_samples,
                                          probs.shape[1]).contiguous().view(
                                              -1, probs.shape[1])
-    q = torch.empty_like(probs).exponential_(1)
+    q = torch.empty_like(probs)
+    if seq_groups is None:
+        q.exponential_()
+    else:
+        sample_idx = 0
+        for (seq_ids, _), generator in zip(seq_groups, generators):
+            next_sample_idx = sample_idx + len(seq_ids) * num_samples
+            q[sample_idx:next_sample_idx].exponential_(generator=generator)
+            sample_idx = next_sample_idx
     return probs.div_(q).argmax(dim=1).view(-1, num_samples)
 
 
@@ -370,6 +380,7 @@ def _sample(
 
     sample_results_dict: Dict[int, Tuple[List[int], List[int]]] = {}
     sample_metadata = {}
+    multinomial_samples = {}
 
     # Counterintiutively, having two loops here is actually faster.
     # The first loop can run without waiting on GPU<->CPU sync.
@@ -385,14 +396,18 @@ def _sample(
                                           is_prompts, sample_indices)
         if sampling_type == SamplingType.GREEDY:
             greedy_samples = torch.argmax(logprobs[sample_indices], dim=-1)
-        elif sampling_type == SamplingType.RANDOM:
+        elif sampling_type in (SamplingType.RANDOM, SamplingType.RANDOM_SEED):
             max_best_of = 1
             for seq_group, is_prompt in zip(seq_groups, is_prompts):
                 if is_prompt:
                     _, sampling_params = seq_group
                     max_best_of = max(max_best_of, sampling_params.best_of)
-            multinomial_samples = _multinomial(probs[sample_indices],
-                                               max_best_of)
+            seeded_args = {} if sampling_type == SamplingType.RANDOM else {
+                "seq_groups": seq_groups,
+                "generators": sampling_metadata.generators,
+            }
+            multinomial_samples[sampling_type] = _multinomial(
+                probs[sample_indices], max_best_of, **seeded_args)
         elif sampling_type == SamplingType.BEAM:
             beam_search_logprobs = logprobs[sample_indices]
         else:
@@ -407,9 +422,9 @@ def _sample(
             sampling_type]
         if sampling_type == SamplingType.GREEDY:
             sample_results = _greedy_sample(seq_groups, greedy_samples)
-        elif sampling_type == SamplingType.RANDOM:
+        elif sampling_type in (SamplingType.RANDOM, SamplingType.RANDOM_SEED):
             sample_results = _random_sample(seq_groups, is_prompts,
-                                            multinomial_samples)
+                                            multinomial_samples[sampling_type])
         elif sampling_type == SamplingType.BEAM:
             sample_results = _beam_search_sample(seq_groups, is_prompts,
                                                  sampling_metadata.seq_data,

vllm/model_executor/sampling_metadata.py

@@ -19,6 +19,7 @@ class SamplingMetadata:
         prompt_lens: Lengths of prompts.
         selected_token_indices: Token indices selected for sampling.
         categorized_sample_indices: SamplingType -> token indices to sample.
+        generators: List of torch.Generators to use for seeded sampling
         perform_sampling: Whether to perform sampling. This option is used to
             make the sampling only happens in the driver worker, and disable
             sampling in other worker processes.
@@ -31,6 +32,7 @@ class SamplingMetadata:
         prompt_lens: Optional[List[int]],
         selected_token_indices: torch.Tensor,
         categorized_sample_indices: Optional[Dict[SamplingType, torch.Tensor]],
+        generators: Optional[List[torch.Generator]] = None,
         perform_sampling: bool = True,
     ) -> None:
         self.seq_groups = seq_groups
@@ -38,6 +40,7 @@ class SamplingMetadata:
         self.prompt_lens = prompt_lens
         self.selected_token_indices = selected_token_indices
         self.categorized_sample_indices = categorized_sample_indices
+        self.generators = generators
         self.perform_sampling = perform_sampling
 
         self.num_prompts = len(prompt_lens) if prompt_lens is not None else 0

vllm/sampling_params.py

@@ -11,7 +11,8 @@ _SAMPLING_EPS = 1e-5
 class SamplingType(IntEnum):
     GREEDY = 0
     RANDOM = 1
-    BEAM = 2
+    RANDOM_SEED = 2
+    BEAM = 3
 
 
 LogitsProcessor = Callable[[List[int], torch.Tensor], torch.Tensor]
@@ -56,6 +57,7 @@ class SamplingParams:
         min_p: Float that represents the minimum probability for a token to be
             considered, relative to the probability of the most likely token.
             Must be in [0, 1]. Set to 0 to disable this.
+        seed: Random seed to use for the generation.
         use_beam_search: Whether to use beam search instead of sampling.
         length_penalty: Float that penalizes sequences based on their length.
             Used in beam search.
@@ -101,6 +103,7 @@ class SamplingParams:
         top_p: float = 1.0,
         top_k: int = -1,
         min_p: float = 0.0,
+        seed: Optional[int] = None,
         use_beam_search: bool = False,
         length_penalty: float = 1.0,
         early_stopping: Union[bool, str] = False,
@@ -124,6 +127,7 @@ class SamplingParams:
         self.top_p = top_p
         self.top_k = top_k
         self.min_p = min_p
+        self.seed = seed
         self.use_beam_search = use_beam_search
         self.length_penalty = length_penalty
         self.early_stopping = early_stopping
@@ -229,6 +233,8 @@ class SamplingParams:
             return SamplingType.BEAM
         if self.temperature < _SAMPLING_EPS:
             return SamplingType.GREEDY
+        if self.seed is not None:
+            return SamplingType.RANDOM_SEED
         return SamplingType.RANDOM
 
     def __repr__(self) -> str:
@@ -242,6 +248,7 @@ class SamplingParams:
             f"top_p={self.top_p}, "
             f"top_k={self.top_k}, "
             f"min_p={self.min_p}, "
+            f"seed={self.seed}, "
             f"use_beam_search={self.use_beam_search}, "
             f"length_penalty={self.length_penalty}, "
             f"early_stopping={self.early_stopping}, "

vllm/sequence.py

@@ -248,6 +248,14 @@ class Sequence:
                 f"num_blocks={len(self.logical_token_blocks)})")
 
 
+@dataclass
+class SequenceGroupState:
+    """Mutable state tied to a specific sequence group"""
+
+    # torch.Generator used in seeded sampling
+    generator: Optional = None
+
+
 class SequenceGroup:
     """A group of sequences that are generated from the same prompt.
 
@@ -280,6 +288,7 @@ class SequenceGroup:
         self.lora_request = lora_request
         self.prefix: Optional[Prefix] = prefix
         self.prompt_logprobs: Optional[PromptLogprobs] = None
+        self.state = SequenceGroupState()
 
     @property
     def prompt(self) -> str:
@@ -397,6 +406,7 @@ class SequenceGroupMetadata:
         sampling_params: The sampling parameters used to generate the outputs.
         block_tables: The block tables. (Seq id -> list of physical block
             numbers)
+        state: Internal state tied to this sequence group.
         lora_request: LoRA request.
         prefix: The prefix of the prompt of the sequence group.
     """
@@ -410,6 +420,7 @@ class SequenceGroupMetadata:
         block_tables: Dict[int, List[int]],
         lora_request: Optional[LoRARequest] = None,
         prefix: Optional[Prefix] = None,
+        state: Optional[SequenceGroupState] = None,
     ) -> None:
         self.request_id = request_id
         self.is_prompt = is_prompt
@@ -418,6 +429,7 @@ class SequenceGroupMetadata:
         self.block_tables = block_tables
         self.lora_request = lora_request
         self.prefix = prefix
+        self.state = SequenceGroupState() if state is None else state
 
     @property
     def lora_int_id(self) -> int:

vllm/worker/model_runner.py

@@ -389,6 +389,7 @@ class ModelRunner:
     ) -> SamplingMetadata:
         seq_groups: List[Tuple[List[int], SamplingParams]] = []
         selected_token_indices: List[int] = []
+        generators: List[torch.Generator] = []
         selected_token_start_idx = 0
         categorized_sample_indices = {t: [] for t in SamplingType}
         categorized_sample_indices_start_idx = 0
@@ -419,6 +420,10 @@ class ModelRunner:
                 selected_token_indices.append(selected_token_start_idx +
                                               subquery_len - 1)
                 selected_token_start_idx += max_subquery_len
+
+                if sampling_params.seed is not None:
+                    seq_group_metadata.state.generator = torch.Generator(
+                        device="cuda").manual_seed(sampling_params.seed)
             else:
                 num_seqs = len(seq_ids)
                 selected_token_indices.extend(
@@ -432,6 +437,9 @@ class ModelRunner:
                               categorized_sample_indices_start_idx + num_seqs))
                 categorized_sample_indices_start_idx += num_seqs
 
+            if sampling_params.seed is not None:
+                generators.append(seq_group_metadata.state.generator)
+
         selected_token_indices = _async_h2d(selected_token_indices,
                                             dtype=torch.long,
                                             target_device=self.device,
@@ -454,6 +462,7 @@ class ModelRunner:
             prompt_lens=prompt_lens,
             selected_token_indices=selected_token_indices,
             categorized_sample_indices=categorized_sample_indices,
+            generators=generators,
         )
         return sampling_metadata
 
@@ -536,6 +545,7 @@ class ModelRunner:
                 prompt_lens=None,
                 selected_token_indices=metadata_dict["selected_token_indices"],
                 categorized_sample_indices=None,
+                generators=None,
                 perform_sampling=False,
             )