[2/N] Chunked prefill data update (#3538)

benchmarks/benchmark_latency.py

@@ -26,7 +26,9 @@ def main(args: argparse.Namespace):
               kv_cache_dtype=args.kv_cache_dtype,
               device=args.device,
               ray_workers_use_nsight=args.ray_workers_use_nsight,
-              download_dir=args.download_dir)
+              enable_chunked_prefill=args.enable_chunked_prefill,
+              download_dir=args.download_dir,
+              block_size=args.block_size)
 
     sampling_params = SamplingParams(
         n=args.n,
@@ -145,6 +147,16 @@ if __name__ == '__main__':
         default="cuda",
         choices=["cuda"],
         help='device type for vLLM execution, supporting CUDA only currently.')
+    parser.add_argument('--block-size',
+                        type=int,
+                        default=16,
+                        help='block size of key/value cache')
+    parser.add_argument(
+        '--enable-chunked-prefill',
+        type=bool,
+        default=False,
+        help='If True, the prefill requests can be chunked based on the '
+        'max_num_batched_tokens')
     parser.add_argument(
         "--ray-workers-use-nsight",
         action='store_true',

tests/conftest.py

@@ -256,6 +256,8 @@ class VllmRunner:
         dtype: str = "half",
         disable_log_stats: bool = True,
         tensor_parallel_size: int = 1,
+        block_size: int = 16,
+        enable_chunked_prefill: bool = False,
         **kwargs,
     ) -> None:
         self.model = LLM(
@@ -266,6 +268,8 @@ class VllmRunner:
             swap_space=0,
             disable_log_stats=disable_log_stats,
             tensor_parallel_size=tensor_parallel_size,
+            block_size=block_size,
+            enable_chunked_prefill=enable_chunked_prefill,
             **kwargs,
         )
 

tests/core/test_scheduler.py

@@ -10,6 +10,10 @@ from vllm.sequence import Logprob, SequenceGroup
 from .utils import create_dummy_prompt
 
 
+def get_sequence_groups(scheduler_output):
+    return [s.seq_group for s in scheduler_output.scheduled_seq_groups]
+
+
 def test_scheduler_add_seq_group():
     block_size = 4
     scheduler_config = SchedulerConfig(100, 64, 1)
@@ -57,9 +61,9 @@ def test_scheduler_schedule_simple():
     cache_config.num_cpu_blocks = 8
     cache_config.num_gpu_blocks = 8
     scheduler = Scheduler(scheduler_config, cache_config, None)
+    running: List[SequenceGroup] = []
 
     # Add seq groups to scheduler.
-    running: List[SequenceGroup] = []
     for i in range(num_seq_group):
         _, seq_group = create_dummy_prompt(str(i), prompt_length=block_size)
         scheduler.add_seq_group(seq_group)
@@ -68,7 +72,7 @@ def test_scheduler_schedule_simple():
     # Schedule seq groups prompts.
     num_tokens = block_size * num_seq_group
     seq_group_meta, out = scheduler.schedule()
-    assert set(out.scheduled_seq_groups) == set(running)
+    assert set(get_sequence_groups(out)) == set(running)
     assert out.num_batched_tokens == num_tokens
     assert (not out.blocks_to_copy and not out.blocks_to_swap_in
             and not out.blocks_to_swap_out)
@@ -76,7 +80,7 @@ def test_scheduler_schedule_simple():
 
     # Schedule seq groups generation.
     seq_group_meta, out = scheduler.schedule()
-    assert set(out.scheduled_seq_groups) == set(running)
+    assert set(get_sequence_groups(out)) == set(running)
     assert out.num_batched_tokens == num_seq_group
     assert (not out.blocks_to_copy and not out.blocks_to_swap_in
             and not out.blocks_to_swap_out)
@@ -100,7 +104,7 @@ def test_scheduler_schedule_preempt_abort():
 
     # Schedule seq groups prompts.
     seq_group_meta, out = scheduler.schedule()
-    assert out.scheduled_seq_groups == [seq_group_a, seq_group_b]
+    assert get_sequence_groups(out) == [seq_group_a, seq_group_b]
     assert out.num_batched_tokens == block_size * 2  # seq_a and seq_b
     assert (not out.blocks_to_copy and not out.blocks_to_swap_in
             and not out.blocks_to_swap_out)
@@ -115,7 +119,7 @@ def test_scheduler_schedule_preempt_abort():
 
     # Schedule seq groups generation and preempt seq group b.
     seq_group_meta, out = scheduler.schedule()
-    assert out.scheduled_seq_groups == [seq_group_a]
+    assert get_sequence_groups(out) == [seq_group_a]
     assert out.num_batched_tokens == 1
     assert (not out.blocks_to_copy and not out.blocks_to_swap_in
             and not out.blocks_to_swap_out)
@@ -125,7 +129,7 @@ def test_scheduler_schedule_preempt_abort():
     # Abort seq group a. Re-schedule seq group b prompt with recomputation.
     scheduler.abort_seq_group("1")
     seq_group_meta, out = scheduler.schedule()
-    assert out.scheduled_seq_groups == [seq_group_b]
+    assert get_sequence_groups(out) == [seq_group_b]
     assert out.num_batched_tokens == 5  # 4 prompt + 1 generation.
     assert (not out.blocks_to_copy and not out.blocks_to_swap_in
             and not out.blocks_to_swap_out)
@@ -155,11 +159,11 @@ def test_scheduler_max_seqs():
 
     # Schedule seq groups prompts.
     _, out = scheduler.schedule()
-    assert set(out.scheduled_seq_groups) == set([all_seq_groups[0]])
+    assert set(get_sequence_groups(out)) == set([all_seq_groups[0]])
 
     # Schedule seq groups generation.
     _, out = scheduler.schedule()
-    assert set(out.scheduled_seq_groups) == set([all_seq_groups[0]])
+    assert set(get_sequence_groups(out)) == set([all_seq_groups[0]])
 
     # Append 2 more seq group
     scheduler.add_seq_group(all_seq_groups[1])
@@ -169,7 +173,7 @@ def test_scheduler_max_seqs():
     # Only 1 seq group should be scheduled since max_seq_group is 2
     # and one is prompting.
     _, out = scheduler.schedule()
-    assert set(out.scheduled_seq_groups) == set([all_seq_groups[1]])
+    assert set(get_sequence_groups(out)) == set([all_seq_groups[1]])
 
 
 def test_scheduler_delay_factor():

tests/test_sequence.py

@@ -1,6 +1,7 @@
 import pytest
 
-from vllm.sequence import SamplerOutput, SequenceGroupOutput, SequenceOutput
+from vllm.sequence import (SamplerOutput, SequenceData, SequenceGroupOutput,
+                           SequenceOutput)
 
 
 @pytest.fixture
@@ -48,3 +49,24 @@ def test_sampler_output_eq(sample_outputs):
     sampler_output3 = SamplerOutput(outputs=sample_outputs[:-1])
     assert sampler_output1 == sampler_output2
     assert sampler_output1 != sampler_output3
+
+
+def test_sequence_data_prefill():
+    seq_data = SequenceData(prompt_token_ids=[1, 2, 3, 4])
+    assert seq_data.get_num_uncomputed_tokens() == 4
+    assert seq_data.get_num_computed_tokens() == 0
+    # advance by 2
+    seq_data.update_num_computed_tokens(2)
+    assert seq_data.get_num_uncomputed_tokens() == 2
+    assert seq_data.get_num_computed_tokens() == 2
+
+    # advance by 1
+    seq_data.update_num_computed_tokens(1)
+    assert seq_data.get_num_uncomputed_tokens() == 1
+    assert seq_data.get_num_computed_tokens() == 3
+
+    # append tokens and reset, simulating recompute
+    seq_data.append_token_id(1, logprob=0.0)
+    seq_data.reset_num_computed_tokens()
+    assert seq_data.get_num_uncomputed_tokens() == 5
+    assert seq_data.get_num_computed_tokens() == 0

tests/worker/test_model_runner.py

@@ -18,15 +18,16 @@ def test_prepare_prompt(batch_size):
         # make sure all tokens fit into one block
         prompt_len = i % (model_runner.block_size - 1) + 1
         prompt_lens.append(prompt_len)
-        seq_data = list(range(prompt_len))
+        seq_data = SequenceData(list(range(prompt_len)))
-        seq_group_metadata_list.append(
+        seq_group_metadata = SequenceGroupMetadata(
-            SequenceGroupMetadata(
             request_id=f"test_{i}",
             is_prompt=True,
-                seq_data={0: SequenceData(seq_data)},
+            seq_data={0: seq_data},
             sampling_params=SamplingParams(temperature=0),
             block_tables=block_tables,
-            ))
+        )
+        assert seq_group_metadata.token_chunk_size == seq_data.get_len()
+        seq_group_metadata_list.append(seq_group_metadata)
 
     expected_selected_token_indices = []
     selected_token_start_idx = 0
@@ -131,14 +132,16 @@ def test_prepare_decode_cuda_graph(batch_size):
         prompt_len = i % (model_runner.block_size - 1) + 1
         prompt_lens.append(prompt_len)
         seq_data = list(range(prompt_len))
-        seq_group_metadata_list.append(
+        seq_data = SequenceData(seq_data)
-            SequenceGroupMetadata(
+        seq_group_metadata = SequenceGroupMetadata(
             request_id=f"test_{i}",
             is_prompt=False,
-                seq_data={0: SequenceData(seq_data)},
+            seq_data={0: seq_data},
             sampling_params=SamplingParams(temperature=0),
             block_tables={0: [1]},
-            ))
+        )
+        assert seq_group_metadata.token_chunk_size == 1
+        seq_group_metadata_list.append(seq_group_metadata)
 
     input_tokens, input_positions, attn_metadata, _, _, _ = (
         model_runner._prepare_decode(seq_group_metadata_list))

vllm/config.py

@@ -533,6 +533,8 @@ class SchedulerConfig:
         delay_factor: Apply a delay (of delay factor multiplied by previous
             prompt latency) before scheduling next prompt.
         use_v2_block_manager: Whether to use the BlockSpaceManagerV2 or not.
+        enable_chunked_prefill: If True, prefill requests can be chunked based
+            on the remaining max_num_batched_tokens.
     """
 
     def __init__(
@@ -542,6 +544,7 @@ class SchedulerConfig:
         max_model_len: int,
         use_v2_block_manager: bool = False,
         delay_factor: float = 0.0,
+        enable_chunked_prefill: bool = False,
     ) -> None:
         if max_num_batched_tokens is not None:
             self.max_num_batched_tokens = max_num_batched_tokens
@@ -553,6 +556,7 @@ class SchedulerConfig:
         self.max_model_len = max_model_len
         self.delay_factor = delay_factor
         self.use_v2_block_manager = use_v2_block_manager
+        self.chunked_prefill_enabled = enable_chunked_prefill
         self._verify_args()
 
     def _verify_args(self) -> None:

vllm/core/scheduler.py

@@ -1,6 +1,7 @@
 import enum
 import time
 from collections import deque
+from dataclasses import dataclass
 from typing import Deque, Dict, Iterable, List, Optional, Set, Tuple, Union
 
 from vllm.config import CacheConfig, LoRAConfig, SchedulerConfig
@@ -27,11 +28,24 @@ class PreemptionMode(enum.Enum):
     RECOMPUTE = enum.auto()
 
 
+# seq_group: SequenceGroup to schedule.
+# token_chunk_size: The number of prefill tokens to be processed in the next
+# step.
+@dataclass
+class ScheduledSequenceGroup:
+    # A sequence group that's scheduled.
+    seq_group: SequenceGroup
+    # The total chunk size (number of tokens) to process for next iteration.
+    # 1 for decoding. Same as prompt tokens for prefill, but if prefill is
+    # chunked, it can be smaller than that.
+    token_chunk_size: int
+
+
 class SchedulerOutputs:
 
     def __init__(
         self,
-        scheduled_seq_groups: Iterable[SequenceGroup],
+        scheduled_seq_groups: Iterable[ScheduledSequenceGroup],
         prompt_run: bool,
         num_batched_tokens: int,
         blocks_to_swap_in: Dict[int, int],
@@ -39,17 +53,41 @@ class SchedulerOutputs:
         blocks_to_copy: Dict[int, List[int]],
         ignored_seq_groups: List[SequenceGroup],
     ) -> None:
-        self.scheduled_seq_groups = scheduled_seq_groups
+        """A list of sequence groups to be scheduled as a single batch.
-        self.prompt_run = prompt_run
+
-        self.num_batched_tokens = num_batched_tokens
+        Args:
-        self.blocks_to_swap_in = blocks_to_swap_in
+            scheduled_seq_groups: A tuple of scheduled sequence group and its
-        self.blocks_to_swap_out = blocks_to_swap_out
+                token chunk size.
-        self.blocks_to_copy = blocks_to_copy
+            prompt_run: True if all sequence groups are in prefill phase.
+                If False, all sequence groups are in decoding phase.
+            num_batched_tokens: Total number of batched tokens.
+            blocks_to_swap_in: Blocks to swap in. Dict of CPU -> GPU block
+                number.
+            blocks_to_swap_out: Blocks to swap out. Dict of GPU -> CPU block
+                number.
+            blocks_to_copy: Blocks to copy. Source to a list of dest blocks.
+            ignored_seq_groups: Sequence groups that are going to be ignored.
+        """
+        # A tuple of scheduled sequence group and its chunk size.
+        self.scheduled_seq_groups: ScheduledSequenceGroup = scheduled_seq_groups
+        # True if all sequence groups are in prefill phase. If False, all
+        # sequence groups are in decoding phase.
+        self.prompt_run: bool = prompt_run
+        # Total number of batched tokens.
+        self.num_batched_tokens: int = num_batched_tokens
+        # Blocks to swap in. Dict of CPU -> GPU block number.
+        self.blocks_to_swap_in: Dict[int, int] = blocks_to_swap_in
+        # Blocks to swap out. Dict of GPU -> CPU block number.
+        self.blocks_to_swap_out: Dict[int, int] = blocks_to_swap_out
+        # Blocks to copy. Source to a list of dest blocks.
+        self.blocks_to_copy: Dict[int, List[int]] = blocks_to_copy
+        # Sequence groups that are going to be ignored.
+        self.ignored_seq_groups: List[SequenceGroup] = ignored_seq_groups
+
         # Swap in and swap out should never happen at the same time.
         assert not (blocks_to_swap_in and blocks_to_swap_out)
-        self.ignored_seq_groups = ignored_seq_groups
 
-        self.num_loras = len(self.lora_requests)
+        self.num_loras: int = len(self.lora_requests)
         if self.num_loras > 0:
             self._sort_by_lora_ids()
 
@@ -59,13 +97,13 @@ class SchedulerOutputs:
                 and not self.blocks_to_swap_out and not self.blocks_to_copy)
 
     def _sort_by_lora_ids(self) -> bool:
-        self.scheduled_seq_groups = sorted(self.scheduled_seq_groups,
+        self.scheduled_seq_groups = sorted(
-                                           key=lambda g:
+            self.scheduled_seq_groups,
-                                           (g.lora_int_id, g.request_id))
+            key=lambda g: (g.seq_group.lora_int_id, g.seq_group.request_id))
 
     @property
     def lora_requests(self) -> Set[LoRARequest]:
-        return {g.lora_request for g in self.scheduled_seq_groups}
+        return {g.seq_group.lora_request for g in self.scheduled_seq_groups}
 
 
 class Scheduler:
@@ -198,11 +236,13 @@ class Scheduler:
                 assert len(waiting_seqs) == 1, (
                     "Waiting sequence group should have only one prompt "
                     "sequence.")
-                num_prompt_tokens = waiting_seqs[0].get_len()
+                # get_len includes output tokens if the request has been
-                if num_prompt_tokens > self.prompt_limit:
+                # preempted.
+                num_prefill_tokens = waiting_seqs[0].get_len()
+                if num_prefill_tokens > self.prompt_limit:
                     logger.warning(
-                        f"Input prompt ({num_prompt_tokens} tokens) is too long"
+                        f"Input prompt ({num_prefill_tokens} tokens) is too "
-                        f" and exceeds limit of {self.prompt_limit}")
+                        f"long and exceeds limit of {self.prompt_limit}")
                     for seq in waiting_seqs:
                         seq.status = SequenceStatus.FINISHED_IGNORED
                     ignored_seq_groups.append(seq_group)
@@ -215,8 +255,8 @@ class Scheduler:
                     break
                 elif can_allocate == AllocStatus.NEVER:
                     logger.warning(
-                        f"Input prompt ({num_prompt_tokens} tokens) is too long"
+                        f"Input prompt ({num_prefill_tokens} tokens) is too "
-                        f" and exceeds the capacity of block_manager")
+                        f"long and exceeds the capacity of block_manager")
                     for seq in waiting_seqs:
                         seq.status = SequenceStatus.FINISHED_IGNORED
                     ignored_seq_groups.append(seq_group)
@@ -235,7 +275,7 @@ class Scheduler:
                         continue
 
                 # If the number of batched tokens exceeds the limit, stop.
-                num_batched_tokens += num_prompt_tokens
+                num_batched_tokens += num_prefill_tokens
                 if (num_batched_tokens >
                         self.scheduler_config.max_num_batched_tokens):
                     break
@@ -253,8 +293,10 @@ class Scheduler:
                 self._allocate(seq_group)
                 self.running.append(seq_group)
                 num_curr_seqs += num_new_seqs
-                scheduled.append(seq_group)
+                scheduled.append(
-
+                    ScheduledSequenceGroup(
+                        seq_group=seq_group,
+                        token_chunk_size=num_prefill_tokens))
             self.waiting.extendleft(leftover_waiting_sequences)
 
             if scheduled or ignored_seq_groups:
@@ -352,7 +394,11 @@ class Scheduler:
             for seq_group in self.running)
 
         scheduler_outputs = SchedulerOutputs(
-            scheduled_seq_groups=self.running,
+            scheduled_seq_groups=[
+                ScheduledSequenceGroup(seq_group=running_group,
+                                       token_chunk_size=1)
+                for running_group in self.running
+            ],
             prompt_run=False,
             num_batched_tokens=num_batched_tokens,
             blocks_to_swap_in=blocks_to_swap_in,
@@ -371,10 +417,14 @@ class Scheduler:
 
         # Create input data structures.
         seq_group_metadata_list: List[SequenceGroupMetadata] = []
-        for seq_group in scheduler_outputs.scheduled_seq_groups:
+        for scheduled_seq_group in scheduler_outputs.scheduled_seq_groups:
+            seq_group = scheduled_seq_group.seq_group
+            token_chunk_size = scheduled_seq_group.token_chunk_size
             seq_group.maybe_set_first_scheduled_time(now)
 
+            # seq_id -> SequenceData
             seq_data: Dict[int, SequenceData] = {}
+            # seq_id -> physical block numbers
             block_tables: Dict[int, List[int]] = {}
 
             for seq in seq_group.get_seqs(status=SequenceStatus.RUNNING):
@@ -393,6 +443,7 @@ class Scheduler:
                 seq_data=seq_data,
                 sampling_params=seq_group.sampling_params,
                 block_tables=block_tables,
+                token_chunk_size=token_chunk_size,
                 lora_request=seq_group.lora_request,
                 computed_block_nums=common_computed_block_nums,
                 state=seq_group.state,
@@ -409,8 +460,9 @@ class Scheduler:
         # batch will have been computed before the next scheduling invocation.
         # This is because the engine assumes that a failure in model execution
         # will crash the vLLM instance / will not retry.
-        for seq_group in scheduler_outputs.scheduled_seq_groups:
+        for scheduled_seq_group in scheduler_outputs.scheduled_seq_groups:
-            self.block_manager.mark_blocks_as_computed(seq_group)
+            self.block_manager.mark_blocks_as_computed(
+                scheduled_seq_group.seq_group)
 
         return seq_group_metadata_list, scheduler_outputs
 
@@ -418,6 +470,7 @@ class Scheduler:
         self.block_manager.fork(parent_seq, child_seq)
 
     def free_seq(self, seq: Sequence) -> None:
+        """Free a sequence from a block table."""
         self.block_manager.free(seq)
 
     def free_finished_seq_groups(self) -> None:
@@ -480,7 +533,8 @@ class Scheduler:
         assert len(seqs) == 1
         for seq in seqs:
             seq.status = SequenceStatus.WAITING
-            self.block_manager.free(seq)
+            self.free_seq(seq)
+            seq.reset_state_for_recompute()
         # NOTE: For FCFS, we insert the preempted sequence group to the front
         # of the waiting queue.
         self.waiting.appendleft(seq_group)

vllm/engine/arg_utils.py

@@ -62,6 +62,7 @@ class EngineArgs:
     image_input_shape: Optional[str] = None
     image_feature_size: Optional[int] = None
     scheduler_delay_factor: float = 0.0
+    enable_chunked_prefill: bool = False
 
     def __post_init__(self):
         if self.tokenizer is None:
@@ -356,6 +357,12 @@ class EngineArgs:
             default=EngineArgs.scheduler_delay_factor,
             help='Apply a delay (of delay factor multiplied by previous'
             'prompt latency) before scheduling next prompt.')
+        parser.add_argument(
+            '--enable-chunked-prefill',
+            type=bool,
+            default=False,
+            help='If True, the prefill requests can be chunked based on the '
+            'max_num_batched_tokens')
         return parser
 
     @classmethod
@@ -394,11 +401,14 @@ class EngineArgs:
                 self.tokenizer_pool_type,
                 self.tokenizer_pool_extra_config,
             ), self.ray_workers_use_nsight)
-        scheduler_config = SchedulerConfig(self.max_num_batched_tokens,
+        scheduler_config = SchedulerConfig(
+            self.max_num_batched_tokens,
             self.max_num_seqs,
             model_config.max_model_len,
             self.use_v2_block_manager,
-                                           self.scheduler_delay_factor)
+            delay_factor=self.scheduler_delay_factor,
+            enable_chunked_prefill=self.enable_chunked_prefill,
+        )
         lora_config = LoRAConfig(
             max_lora_rank=self.max_lora_rank,
             max_loras=self.max_loras,

vllm/engine/llm_engine.py

@@ -553,7 +553,10 @@ class LLMEngine:
         # Update the scheduled sequence groups with the model outputs.
         scheduled_seq_groups = scheduler_outputs.scheduled_seq_groups
 
-        for seq_group, outputs in zip(scheduled_seq_groups, output):
+        for scheduled_seq_group, outputs in zip(scheduled_seq_groups, output):
+            seq_group = scheduled_seq_group.seq_group
+            token_chunk_size = scheduled_seq_group.token_chunk_size
+            seq_group.update_num_computed_tokens(token_chunk_size)
             self._process_sequence_group_outputs(seq_group, outputs)
 
         # Free the finished sequence groups.
@@ -561,7 +564,8 @@ class LLMEngine:
 
         # Create the outputs.
         request_outputs: List[RequestOutput] = []
-        for seq_group in scheduled_seq_groups:
+        for scheduled_seq_group in scheduled_seq_groups:
+            seq_group = scheduled_seq_group.seq_group
             seq_group.maybe_set_first_token_time(now)
             request_output = RequestOutput.from_seq_group(seq_group)
             request_outputs.append(request_output)
@@ -676,17 +680,20 @@ class LLMEngine:
             # Number of Tokens.
             if prompt_run:
                 num_prompt_tokens = sum(
-                    len(seq_group.prompt_token_ids)
+                    len(scheduled_seq_group.seq_group.prompt_token_ids)
-                    for seq_group in scheduler_outputs.scheduled_seq_groups)
+                    for scheduled_seq_group in
+                    scheduler_outputs.scheduled_seq_groups)
                 num_generation_tokens = sum(
-                    seq_group.num_seqs()
+                    scheduled_seq_group.seq_group.num_seqs()
-                    for seq_group in scheduler_outputs.scheduled_seq_groups)
+                    for scheduled_seq_group in
+                    scheduler_outputs.scheduled_seq_groups)
             else:
                 num_generation_tokens = scheduler_outputs.num_batched_tokens
 
             # Latency Timings.
             time_last_iters = []
-            for seq_group in scheduler_outputs.scheduled_seq_groups:
+            for scheduled_seq_group in scheduler_outputs.scheduled_seq_groups:
+                seq_group = scheduled_seq_group.seq_group
                 # Time since last token.
                 # (n.b. updates seq_group.metrics.last_token_time)
                 time_last_iters.append(seq_group.get_last_latency(now))

vllm/sequence.py

@@ -113,6 +113,8 @@ class SequenceData:
         self.prompt_token_ids = prompt_token_ids
         self.output_token_ids = output_token_ids
         self.cumulative_logprob = 0.0
+        # The number of tokens that are computed (that run against the model).
+        self._num_computed_tokens = 0
 
     def append_token_id(self, token_id: int, logprob: float) -> None:
         self.output_token_ids.append(token_id)
@@ -130,6 +132,28 @@ class SequenceData:
     def get_token_ids(self) -> List[int]:
         return self.prompt_token_ids + self.output_token_ids
 
+    def get_num_computed_tokens(self) -> int:
+        """Return the number of prefill tokens that are already computed."""
+        return self._num_computed_tokens
+
+    def update_num_computed_tokens(self, num_new_computed_tokens: int) -> int:
+        """Update number of tokens computed so far."""
+        self._num_computed_tokens += num_new_computed_tokens
+
+    def reset_num_computed_tokens(self) -> None:
+        """Reset the number of computed tokens from this sequence. It is
+        supposed to be called when a sequence needs to be started from
+        the beginning again (e.g., sequence is preempted).
+        """
+        self._num_computed_tokens = 0
+
+    def get_num_uncomputed_tokens(self) -> int:
+        """Return the number of prefil tokens that are not computed."""
+        # we use `get_len()` which includes prompt_len + output_len instead
+        # of prompt_len here. This is because during recompute we need to
+        # prefill for both prompt and output.
+        return self.get_len() - self.get_num_computed_tokens()
+
     def get_last_token_id(self) -> int:
         if not self.output_token_ids:
             return self.prompt_token_ids[-1]
@@ -208,6 +232,10 @@ class Sequence:
     def num_hashed_tokens_of_block(self, logical_idx: int):
         return logical_idx * self.block_size + self.block_size
 
+    def reset_state_for_recompute(self):
+        """Reset the sequence states for recomputation."""
+        self.data.reset_num_computed_tokens()
+
     def _append_logical_block(self) -> None:
         block = LogicalTokenBlock(
             block_number=len(self.logical_token_blocks),
@@ -430,6 +458,18 @@ class SequenceGroup:
     def get_finished_seqs(self) -> List[Sequence]:
         return [seq for seq in self.seqs_dict.values() if seq.is_finished()]
 
+    def update_num_computed_tokens(self, num_new_computed_tokens: int):
+        """Update number of tokens computed so far."""
+        for seq in self.seqs_dict.values():
+            seq.data.update_num_computed_tokens(num_new_computed_tokens)
+
+    def get_num_uncomputed_tokens(self) -> int:
+        # All sequences in the group should have the same prompt, so the
+        # number of unfinished prefill tokens are the same across all
+        # sequences.
+        return list(
+            self.seqs_dict.values())[0].data.get_num_uncomputed_tokens()
+
     def num_seqs(self, status: Optional[SequenceStatus] = None) -> int:
         return len(self.get_seqs(status))
 
@@ -473,6 +513,8 @@ class SequenceGroupMetadata:
         sampling_params: The sampling parameters used to generate the outputs.
         block_tables: The block tables. (Seq id -> list of physical block
             numbers)
+        token_chunk_size: The number of tokens to be processed. None if
+            chunking is not required.
         state: Internal state tied to this sequence group.
         lora_request: LoRA request.
         multi_modal_data: Multi modal data.
@@ -485,6 +527,7 @@ class SequenceGroupMetadata:
         seq_data: Dict[int, SequenceData],
         sampling_params: SamplingParams,
         block_tables: Dict[int, List[int]],
+        token_chunk_size: Optional[int] = None,
         lora_request: Optional[LoRARequest] = None,
         computed_block_nums: Optional[List[int]] = None,
         state: Optional[SequenceGroupState] = None,
@@ -499,11 +542,23 @@ class SequenceGroupMetadata:
         self.computed_block_nums = computed_block_nums
         self.multi_modal_data = multi_modal_data
         self.state = SequenceGroupState() if state is None else state
+        self._token_chunk_size = token_chunk_size
+
+        if self._token_chunk_size is None:
+            if is_prompt:
+                self._token_chunk_size = list(seq_data.values())[0].get_len()
+            else:
+                self._token_chunk_size = 1
 
     @property
     def lora_int_id(self) -> int:
         return self.lora_request.lora_int_id if self.lora_request else 0
 
+    @property
+    def token_chunk_size(self) -> int:
+        """Return the number of tokens to be processed (chunk size)."""
+        return self._token_chunk_size
+
 
 class SequenceOutput:
     """The model output associated with a sequence.

vllm/worker/model_runner.py

@@ -150,39 +150,58 @@ class ModelRunner:
         subquery_lens: List[int] = []
         prefix_block_tables: List[List[int]] = []
         multi_modal_input_list: List[torch.Tensor] = []
+
         for seq_group_metadata in seq_group_metadata_list:
             assert seq_group_metadata.is_prompt
             seq_ids = list(seq_group_metadata.seq_data.keys())
             assert len(seq_ids) == 1
             seq_id = seq_ids[0]
 
+            computed_block_nums = seq_group_metadata.computed_block_nums
+            if (self.scheduler_config is not None
+                    and self.scheduler_config.chunked_prefill_enabled
+                    and computed_block_nums is not None):
+                raise RuntimeError(
+                    "chunked prefill cannot be used with prefix caching "
+                    "now.")
+
+            token_chunk_size = seq_group_metadata.token_chunk_size
             seq_data = seq_group_metadata.seq_data[seq_id]
-            prompt_tokens = seq_data.get_token_ids()
+            computed_len = seq_data.get_num_computed_tokens()
+            # We should use get_len here because in case of preemption
+            # it contains output tokens.
+            prefill_end = min(seq_data.get_len(),
+                              computed_len + token_chunk_size)
+            # TODO(sang): Rename it after chunked prefill is introduced.
+            prompt_tokens = seq_data.get_token_ids()[computed_len:prefill_end]
             prompt_len = len(prompt_tokens)
+            # Right now, the prefill_end is always same as the length of
+            # sequence. However, once chunked prefill is introduced, this
+            # assumption can be changed.
+            assert prefill_end == seq_data.get_len()
             prompt_lens.append(prompt_len)
-            computed_len = 0
 
             # NOTE: This only works for oooooooxxx style attention.
-            computed_block_nums = seq_group_metadata.computed_block_nums
             if computed_block_nums is not None and len(
                     computed_block_nums) > 0 and self.sliding_window is None:
                 # Prefix is not supported with sliding_window
                 computed_len = len(computed_block_nums) * self.block_size
                 prompt_tokens = prompt_tokens[computed_len:]
                 prefix_block_tables.append(computed_block_nums)
-                context_len = computed_len
             else:
                 prefix_block_tables.append([])
-                context_len = 0
+                # Right now, prefill start is always 0. However, this
+                # assumption can be changed once chunked prefill is introduced.
+                assert computed_len == 0
+
             # actual prompt lens
-            context_lens.append(context_len)
+            context_lens.append(computed_len)
             subquery_lens.append(prompt_len - computed_len)
 
             input_tokens.extend(prompt_tokens)
             # NOTE(woosuk): Here we assume that the first token in the prompt
             # is always the first token in the sequence.
-            input_positions.extend(
+            input_positions.extend(list(range(computed_len, prefill_end)))
-                list(range(computed_len, computed_len + len(prompt_tokens))))
 
             lora_id = seq_group_metadata.lora_int_id
 
@@ -218,7 +237,8 @@ class ModelRunner:
                     "Prefix caching is currently not supported with "
                     "sliding window attention")
                 start_idx = max(0, prompt_len - self.sliding_window)
-            for i in range(computed_len, prompt_len):
+
+            for i in range(computed_len, prefill_end):
                 if i < start_idx:
                     slot_mapping.append(_PAD_SLOT_ID)
                     continue
@@ -331,6 +351,7 @@ class ModelRunner:
 
         for seq_group_metadata in seq_group_metadata_list:
             assert not seq_group_metadata.is_prompt
+            assert seq_group_metadata.token_chunk_size == 1
 
             seq_ids = list(seq_group_metadata.seq_data.keys())
             lora_id = seq_group_metadata.lora_int_id