vllm.v1.worker.gpu.model_runner ¶

class GPUModelRunner(LoRAModelRunnerMixin):
    def __init__(
        self,
        vllm_config: VllmConfig,
        device: torch.device,
    ):
        self.vllm_config = vllm_config
        self.model_config = vllm_config.model_config
        self.cache_config = vllm_config.cache_config
        self.compilation_config = vllm_config.compilation_config
        self.lora_config = vllm_config.lora_config
        self.load_config = vllm_config.load_config
        self.parallel_config = vllm_config.parallel_config
        self.scheduler_config = vllm_config.scheduler_config
        self.speculative_config = vllm_config.speculative_config
        self.observability_config = vllm_config.observability_config

        self.device = device
        self.dtype = self.model_config.dtype
        self.kv_cache_dtype = self.dtype
        if self.cache_config.cache_dtype != "auto":
            # Quantized KV cache.
            self.kv_cache_dtype = STR_DTYPE_TO_TORCH_DTYPE[
                self.cache_config.cache_dtype
            ]
        self.is_pooling_model = False

        self.vocab_size = self.model_config.get_vocab_size()
        self.max_model_len = self.model_config.max_model_len
        self.max_num_tokens = self.scheduler_config.max_num_batched_tokens
        self.max_num_reqs = self.scheduler_config.max_num_seqs
        self.inputs_embeds_size = self.model_config.get_inputs_embeds_size()

        # Multimodal
        self.mm_registry = MULTIMODAL_REGISTRY
        self.supports_mm_inputs = self.mm_registry.supports_multimodal_inputs(
            self.model_config
        )
        if self.supports_mm_inputs:
            self.encoder_runner = EncoderRunner(
                max_num_tokens=self.max_num_tokens,
                hidden_size=self.inputs_embeds_size,
                dtype=self.dtype,
                device=self.device,
            )
        self.uses_mrope = self.model_config.uses_mrope
        if self.uses_mrope:
            self.mrope_states = MRopeState(
                max_num_reqs=self.max_num_reqs,
                max_num_tokens=self.max_num_tokens,
                max_model_len=self.max_model_len,
                device=self.device,
            )

        self.use_async_scheduling = self.scheduler_config.async_scheduling
        self.output_copy_stream = torch.cuda.Stream(self.device)
        self.output_copy_event = torch.cuda.Event()
        if self.use_async_scheduling:
            self.input_prep_event = torch.cuda.Event()
            self.structured_outputs_event = torch.cuda.Event()
        else:
            self.input_prep_event = None
            self.structured_outputs_event = None

        if self.speculative_config is not None:
            self.do_spec_decode = True
            self.num_speculative_steps = self.speculative_config.num_speculative_tokens
            self.speculator = init_speculator(self.vllm_config, self.device)
        else:
            self.do_spec_decode = False
            self.num_speculative_steps = 0
            self.speculator = None

        self.req_states = RequestState(
            max_num_reqs=self.max_num_reqs,
            max_model_len=self.max_model_len,
            max_num_batched_tokens=self.max_num_tokens,
            num_speculative_steps=self.num_speculative_steps,
            vocab_size=self.vocab_size,
            device=self.device,
        )
        self.input_buffers = InputBuffers(
            max_num_reqs=self.max_num_reqs,
            max_num_tokens=self.max_num_tokens,
            device=self.device,
        )
        self.sampler = Sampler(
            max_num_reqs=self.max_num_reqs,
            vocab_size=self.vocab_size,
            device=self.device,
            logprobs_mode=self.model_config.logprobs_mode,
        )
        self.prompt_logprobs_worker = PromptLogprobsWorker(self.max_num_reqs)

        # CUDA graphs.
        self.cudagraph_manager = CudaGraphManager(
            self.vllm_config, self.uses_mrope, self.device
        )
        # Structured outputs worker.
        self.structured_outputs_worker = StructuredOutputsWorker(
            max_num_logits=self.max_num_reqs * (self.num_speculative_steps + 1),
            vocab_size=self.vocab_size,
        )

        # Buffers for CPU-to-GPU copies.
        self.tmp_idx_mapping = UvaBufferPool(self.max_num_reqs, torch.int32)
        self.tmp_cu_num_logits = UvaBufferPool(self.max_num_reqs + 1, torch.int32)
        self.tmp_query_start_loc = UvaBufferPool(self.max_num_reqs + 1, torch.int32)

        self.kv_connector: KVConnector = NO_OP_KV_CONNECTOR

    def update_max_model_len(self, max_model_len: int) -> None:
        self.max_model_len = max_model_len
        self.req_states.max_model_len = max_model_len

    def get_supported_tasks(self) -> tuple[str]:
        return ("generate",)

    def load_model(self, *args, **kwargs) -> None:
        time_before_load = time.perf_counter()
        with DeviceMemoryProfiler() as m:
            model_loader = get_model_loader(self.vllm_config.load_config)
            logger.info("Loading model from scratch...")

            self.model = model_loader.load_model(
                vllm_config=self.vllm_config,
                model_config=self.vllm_config.model_config,
            )
            if self.lora_config:
                self.model = self.load_lora_model(
                    self.model,
                    self.vllm_config,
                    self.device,
                )
            if self.do_spec_decode:
                self.speculator.load_model(self.model)
        time_after_load = time.perf_counter()

        self.model_memory_usage = m.consumed_memory
        logger.info(
            "Model loading took %s GiB and %.6f seconds",
            format_gib(m.consumed_memory),
            time_after_load - time_before_load,
        )

        prepare_communication_buffer_for_model(self.model)
        if self.do_spec_decode:
            speculator_model = getattr(self.speculator, "model", None)
            if speculator_model is not None:
                prepare_communication_buffer_for_model(speculator_model)

    def get_model(self) -> nn.Module:
        return self.model

    def get_kv_cache_spec(self):
        return get_kv_cache_spec(self.vllm_config)

    def initialize_kv_cache(self, kv_cache_config: KVCacheConfig) -> None:
        kv_cache_config = deepcopy(kv_cache_config)
        self.kv_cache_config = kv_cache_config
        block_sizes = [
            kv_cache_group.kv_cache_spec.block_size
            for kv_cache_group in kv_cache_config.kv_cache_groups
        ]

        self.block_tables = BlockTables(
            block_sizes=block_sizes,
            max_num_reqs=self.max_num_reqs,
            max_num_batched_tokens=self.max_num_tokens,
            max_model_len=self.max_model_len,
            device=self.device,
        )

        self.attn_backends, self.attn_metadata_builders = init_attn_backend(
            self.kv_cache_config,
            self.vllm_config,
            self.device,
        )
        if self.do_spec_decode:
            # HACK(woosuk)
            self.speculator.set_attn(
                self.kv_cache_config,
                self.attn_metadata_builders,
                self.block_tables,
            )

        self.kv_caches: list[torch.Tensor] = []
        kv_caches_dict = init_kv_cache(
            self.kv_caches,
            self.compilation_config.static_forward_context,
            self.kv_cache_config,
            self.attn_backends,
            self.device,
        )
        self.kv_connector = get_kv_connector(self.vllm_config, kv_caches_dict)

        # Attention groups are not supported.
        self.attn_groups = []  # type: ignore

    def prepare_dummy_attn_metadata(self, input_batch: InputBatch) -> None:
        block_tables = self.block_tables.get_dummy_block_tables(input_batch.num_reqs)
        slot_mappings = self.block_tables.get_dummy_slot_mappings(
            input_batch.num_tokens
        )
        attn_metadata = build_attn_metadata(
            attn_metadata_builders=self.attn_metadata_builders,
            num_reqs=input_batch.num_reqs,
            num_tokens=input_batch.num_tokens,
            query_start_loc_gpu=input_batch.query_start_loc,
            query_start_loc_cpu=torch.from_numpy(input_batch.query_start_loc_np),
            seq_lens=input_batch.seq_lens,
            max_seq_len=self.max_model_len,
            block_tables=block_tables,
            slot_mappings=slot_mappings,
            kv_cache_config=self.kv_cache_config,
        )
        input_batch.attn_metadata = attn_metadata

    @torch.inference_mode()
    def _dummy_run(
        self,
        num_tokens: int,
        *args,
        skip_attn: bool = True,
        **kwargs,
    ) -> tuple[torch.Tensor, torch.Tensor]:
        # Create a dummy scheduler output.
        num_reqs = min(num_tokens, self.max_num_reqs)
        num_tokens_per_request = [num_tokens // num_reqs] * num_reqs
        num_tokens_per_request[-1] += num_tokens % num_reqs
        assert sum(num_tokens_per_request) == num_tokens
        num_scheduled_tokens = {
            f"_dummy_req_{i}": n for i, n in enumerate(num_tokens_per_request)
        }
        dummy_scheduler_output = SchedulerOutput.make_empty()
        dummy_scheduler_output.total_num_scheduled_tokens = num_tokens
        dummy_scheduler_output.num_scheduled_tokens = num_scheduled_tokens

        # Disable any use of KVConnector for dummy runs.
        self.kv_connector.set_disabled(True)

        # Execute the model.
        self.execute_model(
            dummy_scheduler_output, dummy_run=True, skip_attn_for_dummy_run=skip_attn
        )
        self.kv_connector.set_disabled(False)
        assert self.execute_model_state is not None
        hidden_states, input_batch, _ = self.execute_model_state
        sample_hidden_states = hidden_states[input_batch.logits_indices]
        return hidden_states, sample_hidden_states

    @torch.inference_mode()
    def _dummy_sampler_run(
        self,
        hidden_states: torch.Tensor,
    ) -> None:
        num_reqs = hidden_states.shape[0]
        logits = self.model.compute_logits(hidden_states)
        idx_mapping = torch.arange(num_reqs, dtype=torch.int32, device=self.device)
        idx_mapping_np = np.arange(num_reqs, dtype=np.int32)
        pos = torch.zeros(num_reqs, dtype=torch.int64, device=self.device)
        # NOTE(woosuk): During the initial memory profiling, the sampler may skip
        # top_k, top_p, and logprobs, using less GPU memory than what is possible
        # during actual execution.
        self.sampler(logits, idx_mapping, idx_mapping_np, pos)

    @torch.inference_mode()
    def profile_run(self) -> None:
        hidden_states, sample_hidden_states = self._dummy_run(
            self.max_num_tokens,
            skip_attn=True,
        )
        self._dummy_sampler_run(sample_hidden_states)
        if self.do_spec_decode:
            num_tokens_across_dp = make_num_tokens_across_dp(
                self.parallel_config.data_parallel_size, self.max_num_tokens
            )
            self.speculator.run_model(
                self.max_num_tokens,
                attn_metadata=None,
                num_tokens_across_dp=num_tokens_across_dp,
            )
        torch.cuda.synchronize()
        del hidden_states, sample_hidden_states
        gc.collect()

    def reset_mm_cache(self) -> None:
        pass

    def _get_num_input_tokens(self, num_scheduled_tokens: int) -> int:
        # SP is not supported yet.
        return num_scheduled_tokens

    @torch.inference_mode()
    def capture_model(self) -> int:
        if not self.cudagraph_manager.needs_capture():
            logger.warning(
                "Skipping CUDA graph capture. To turn on CUDA graph capture, "
                "ensure `cudagraph_mode` was not manually set to `NONE`"
            )
            return 0

        start_time = time.perf_counter()
        gc.collect()
        torch.cuda.empty_cache()
        start_free_gpu_memory = torch.cuda.mem_get_info()[0]

        with self.maybe_setup_dummy_loras(self.lora_config):
            mrope_positions = None
            if self.uses_mrope:
                mrope_positions = self.mrope_states.mrope_positions
            inputs_embeds = None
            if self.supports_mm_inputs:
                inputs_embeds = self.encoder_runner.inputs_embeds
            self.cudagraph_manager.capture(
                model=self.model,
                input_buffers=self.input_buffers,
                mrope_positions=mrope_positions,
                inputs_embeds=inputs_embeds,
                block_tables=self.block_tables,
                attn_metadata_builders=self.attn_metadata_builders,
                kv_cache_config=self.kv_cache_config,
            )
            if self.do_spec_decode:
                self.speculator.capture_model()

        end_time = time.perf_counter()
        end_free_gpu_memory = torch.cuda.mem_get_info()[0]
        elapsed_time = end_time - start_time
        cuda_graph_size = start_free_gpu_memory - end_free_gpu_memory
        # This usually takes 5~20 seconds.
        logger.info(
            "Graph capturing finished in %.0f secs, took %.2f GiB",
            elapsed_time,
            cuda_graph_size / (1 << 30),
        )
        return cuda_graph_size

    def warmup_for_prefill(self) -> None:
        # For FlashInfer, we would like to execute a dummy prefill run
        # to trigger JIT compilation.
        if all("FLASHINFER" in b.get_name() for b in self.attn_backends.values()):
            self._dummy_run(self.max_num_tokens, skip_attn=False)
            torch.cuda.synchronize()

    def finish_requests(self, scheduler_output: SchedulerOutput) -> None:
        if scheduler_output.preempted_req_ids is not None:
            for req_id in scheduler_output.preempted_req_ids:
                self.req_states.remove_request(req_id)
                if self.supports_mm_inputs:
                    self.encoder_runner.remove_request(req_id)
                self.prompt_logprobs_worker.remove_request(req_id)
        for req_id in scheduler_output.finished_req_ids:
            self.req_states.remove_request(req_id)
            if self.supports_mm_inputs:
                self.encoder_runner.remove_request(req_id)
            self.prompt_logprobs_worker.remove_request(req_id)

    def free_states(self, scheduler_output: SchedulerOutput) -> None:
        if self.supports_mm_inputs:
            for mm_hash in scheduler_output.free_encoder_mm_hashes:
                self.encoder_runner.free_encoder_cache(mm_hash)

    def add_requests(self, scheduler_output: SchedulerOutput) -> None:
        for new_req_data in scheduler_output.scheduled_new_reqs:
            assert new_req_data.prompt_token_ids is not None
            assert new_req_data.prefill_token_ids is not None
            assert new_req_data.sampling_params is not None
            req_id = new_req_data.req_id
            prompt_len = len(new_req_data.prompt_token_ids)
            self.req_states.add_request(
                req_id=req_id,
                prompt_len=prompt_len,
                prefill_token_ids=new_req_data.prefill_token_ids,
                num_computed_tokens=new_req_data.num_computed_tokens,
                lora_request=new_req_data.lora_request,
            )
            req_index = self.req_states.req_id_to_index[req_id]

            if self.supports_mm_inputs:
                self.encoder_runner.add_request(req_id, new_req_data.mm_features)

            # Pre-compute M-RoPE positions for prefill.
            if self.uses_mrope:
                self.mrope_states.init_prefill_mrope_positions(
                    req_index,
                    self.model,  # type: ignore
                    new_req_data.prefill_token_ids,
                    mm_features=new_req_data.mm_features,
                )

            self.block_tables.append_block_ids(
                req_index, new_req_data.block_ids, overwrite=True
            )
            self.sampler.add_request(
                req_index, prompt_len, new_req_data.sampling_params
            )
            self.prompt_logprobs_worker.add_request(
                req_id, req_index, new_req_data.sampling_params
            )

        if scheduler_output.scheduled_new_reqs:
            self.req_states.apply_staged_writes()
            self.sampler.apply_staged_writes(
                self.req_states.prefill_token_ids.gpu,
                self.req_states.prefill_len.np,
                self.req_states.prompt_len,
            )
            if self.uses_mrope:
                self.mrope_states.apply_staged_writes()

    def update_requests(self, scheduler_output: SchedulerOutput) -> None:
        # Add new blocks for the existing requests.
        cached_reqs = scheduler_output.scheduled_cached_reqs
        for i, req_id in enumerate(cached_reqs.req_ids):
            req_index = self.req_states.req_id_to_index[req_id]
            req_new_block_ids = cached_reqs.new_block_ids[i]
            if req_new_block_ids is not None:
                self.block_tables.append_block_ids(
                    req_index, req_new_block_ids, overwrite=False
                )

    def prepare_inputs(
        self,
        scheduler_output: SchedulerOutput,
        num_tokens_after_padding: int,
    ) -> InputBatch:
        num_tokens = scheduler_output.total_num_scheduled_tokens
        assert num_tokens > 0
        num_reqs = len(scheduler_output.num_scheduled_tokens)

        # Decode first, then prefill.
        # batch_idx -> req_id
        req_ids = sorted(
            scheduler_output.num_scheduled_tokens.keys(),
            key=lambda k: scheduler_output.num_scheduled_tokens[k],
        )
        num_scheduled_tokens = np.array(
            [scheduler_output.num_scheduled_tokens[i] for i in req_ids], dtype=np.int32
        )

        idx_mapping_list = [
            self.req_states.req_id_to_index[req_id] for req_id in req_ids
        ]
        idx_mapping_np = np.array(idx_mapping_list, dtype=np.int32)
        idx_mapping = self.tmp_idx_mapping.copy_to_gpu(idx_mapping_np)

        # Get the number of draft tokens for each request.
        if not scheduler_output.scheduled_spec_decode_tokens:
            # No draft token scheduled (common case).
            total_num_draft_tokens = 0
            total_num_logits = num_reqs
            cu_num_logits_np = np.arange(num_reqs + 1, dtype=np.int32)
            cu_num_logits = torch.arange(
                num_reqs + 1, device=self.device, dtype=torch.int32
            )
            expanded_idx_mapping = idx_mapping
        else:
            draft_tokens = scheduler_output.scheduled_spec_decode_tokens
            num_draft_tokens = np.array(
                [
                    len(draft_tokens[req_id]) if req_id in draft_tokens else 0
                    for req_id in req_ids
                ],
                dtype=np.int32,
            )
            total_num_draft_tokens = int(num_draft_tokens.sum())
            total_num_logits = num_reqs + total_num_draft_tokens

            num_logits = num_draft_tokens + 1
            cu_num_logits_np = np.empty(num_reqs + 1, dtype=np.int32)
            cu_num_logits_np[0] = 0
            np.cumsum(num_logits, out=cu_num_logits_np[1:])
            cu_num_logits = self.tmp_cu_num_logits.copy_to_gpu(cu_num_logits_np)

            expanded_idx_mapping = expand_idx_mapping(
                idx_mapping,
                total_num_logits,
                cu_num_logits,
                max_expand_len=self.num_speculative_steps + 1,
            )

        # Block tables: num_kv_cache_groups x [num_reqs, max_num_blocks]
        block_tables = self.block_tables.gather_block_tables(idx_mapping)

        # Get query_start_loc.
        query_start_loc_np = np.empty(self.max_num_reqs + 1, dtype=np.int32)
        query_start_loc_np[0] = 0
        np.cumsum(num_scheduled_tokens, out=query_start_loc_np[1 : num_reqs + 1])
        # Pad for full CUDA graph mode.
        # Some attention backends like FA3 require query_start_loc to be non-decreasing.
        query_start_loc_np[num_reqs + 1 :] = num_tokens
        self.tmp_query_start_loc.copy_to_gpu(
            query_start_loc_np,
            out=self.input_buffers.query_start_loc,
        )
        query_start_loc_np = query_start_loc_np[: num_reqs + 1]
        query_start_loc_cpu = torch.from_numpy(query_start_loc_np)
        query_start_loc = self.input_buffers.query_start_loc[: num_reqs + 1]

        # Get prefill tokens.
        prepare_prefill_inputs(
            self.input_buffers.input_ids,
            self.req_states.next_prefill_tokens,
            idx_mapping,
            query_start_loc,
            self.req_states.prefill_token_ids.gpu,
            self.req_states.prefill_len.gpu,
            self.req_states.num_computed_tokens.gpu,
        )

        # Prepare positions and seq_lens.
        prepare_pos_seq_lens(
            idx_mapping,
            query_start_loc,
            self.req_states.num_computed_tokens.gpu,
            self.input_buffers.positions,
            self.input_buffers.seq_lens,
        )
        seq_lens = self.input_buffers.seq_lens[:num_reqs]

        # Prepare M-RoPE positions.
        if self.uses_mrope:
            self.mrope_states.prepare_mrope_positions(
                idx_mapping,
                query_start_loc,
                self.req_states.prefill_len.gpu,
                self.req_states.num_computed_tokens.gpu,
            )

        # Some input token ids are directly read from the last sampled tokens
        # and draft tokens. Also, get the logits indices to sample tokens from.
        logits_indices = combine_sampled_and_draft_tokens(
            self.input_buffers.input_ids,
            idx_mapping,
            self.req_states.last_sampled_tokens,
            query_start_loc,
            seq_lens,
            self.req_states.prefill_len.gpu,
            self.req_states.draft_tokens,
            cu_num_logits,
            total_num_logits,
        )

        # Compute slot mappings: [num_kv_cache_groups, num_tokens]
        slot_mappings = self.block_tables.compute_slot_mappings(
            idx_mapping,
            query_start_loc,
            self.input_buffers.positions[:num_tokens],
        )

        # Layer name -> attention metadata.
        attn_metadata = build_attn_metadata(
            attn_metadata_builders=self.attn_metadata_builders,
            num_reqs=num_reqs,
            num_tokens=num_tokens,
            query_start_loc_gpu=query_start_loc,
            query_start_loc_cpu=query_start_loc_cpu,
            seq_lens=self.input_buffers.seq_lens,
            max_seq_len=self.max_model_len,
            block_tables=block_tables,
            slot_mappings=slot_mappings,
            kv_cache_config=self.kv_cache_config,
        )

        input_ids = self.input_buffers.input_ids[:num_tokens_after_padding]
        positions = self.input_buffers.positions[:num_tokens_after_padding]
        mrope_positions = None
        if self.uses_mrope:
            mrope_positions = self.mrope_states.mrope_positions[
                :, :num_tokens_after_padding
            ]
        return InputBatch(
            req_ids=req_ids,
            num_reqs=num_reqs,
            idx_mapping=idx_mapping,
            idx_mapping_np=idx_mapping_np,
            expanded_idx_mapping=expanded_idx_mapping,
            num_scheduled_tokens=num_scheduled_tokens,
            num_tokens=num_tokens,
            num_tokens_after_padding=num_tokens_after_padding,
            num_draft_tokens=total_num_draft_tokens,
            query_start_loc=query_start_loc,
            query_start_loc_np=query_start_loc_np,
            seq_lens=seq_lens,
            input_ids=input_ids,
            positions=positions,
            mrope_positions=mrope_positions,
            inputs_embeds=None,
            attn_metadata=attn_metadata,
            logits_indices=logits_indices,
            cu_num_logits=cu_num_logits,
            cu_num_logits_np=cu_num_logits_np,
        )

    @torch.inference_mode()
    def get_mm_embeddings(
        self,
        scheduled_encoder_inputs: dict[str, list[int]],
        input_batch: InputBatch,
    ) -> tuple[list[torch.Tensor], torch.Tensor]:
        mm_hashes, mm_kwargs = self.encoder_runner.prepare_mm_inputs(
            scheduled_encoder_inputs
        )
        self.encoder_runner.execute_mm_encoder(self.model, mm_hashes, mm_kwargs)
        mm_embeds, is_mm_embed = self.encoder_runner.gather_mm_embeddings(
            input_batch.req_ids,
            input_batch.num_tokens,
            input_batch.num_scheduled_tokens,
            input_batch.query_start_loc_np,
            self.req_states.prefill_len.np[input_batch.idx_mapping_np],
            self.req_states.num_computed_prefill_tokens[input_batch.idx_mapping_np],
        )
        return mm_embeds, is_mm_embed

    def sample(
        self,
        hidden_states: torch.Tensor,
        input_batch: InputBatch,
        grammar_output: GrammarOutput | None,
    ) -> tuple[SamplerOutput, torch.Tensor, torch.Tensor]:
        sample_hidden_states = hidden_states[input_batch.logits_indices]
        sample_pos = input_batch.positions[input_batch.logits_indices]
        logits = self.model.compute_logits(sample_hidden_states)
        if grammar_output is not None:
            # Apply grammar bitmask to the logits in-place.
            self.structured_outputs_worker.apply_grammar_bitmask(
                logits,
                input_batch,
                grammar_output.structured_output_request_ids,
                grammar_output.grammar_bitmask,
            )

        # Sample tokens and compute logprobs (if needed).
        sampler_output = self.sampler(
            logits,
            input_batch.expanded_idx_mapping,
            input_batch.idx_mapping_np,
            sample_pos,
        )

        if input_batch.num_draft_tokens == 0:
            # No draft tokens (common case).
            num_sampled = torch.ones(
                input_batch.num_reqs, dtype=torch.int32, device=self.device
            )
        else:
            # Rejection sampling for spec decoding.
            input_ids = input_batch.input_ids[input_batch.logits_indices]
            sampled_tokens, num_sampled = rejection_sample(
                sampler_output.sampled_token_ids,
                input_ids,
                input_batch.cu_num_logits,
                self.num_speculative_steps,
            )
            sampler_output.sampled_token_ids = sampled_tokens

        # Get the number of sampled and rejected tokens.
        # For chunked prefills, num_sampled and num_rejected are both 0.
        num_sampled, num_rejected = get_num_sampled_and_rejected(
            num_sampled,
            input_batch.seq_lens,
            input_batch.cu_num_logits,
            input_batch.idx_mapping,
            self.req_states.prefill_len.gpu,
        )
        return sampler_output, num_sampled, num_rejected

    def postprocess(
        self,
        input_batch: InputBatch,
        sampled_tokens: torch.Tensor,
        num_sampled: torch.Tensor,
        num_rejected: torch.Tensor,
    ) -> None:
        # Update the number of computed tokens.
        post_update(
            input_batch.idx_mapping,
            self.req_states.num_computed_tokens.gpu,
            self.req_states.last_sampled_tokens,
            self.sampler.penalties_state.output_bin_counts,
            sampled_tokens,
            num_sampled,
            num_rejected,
            input_batch.query_start_loc,
        )

        # Update the number of computed prefill tokens.
        idx_mapping_np = input_batch.idx_mapping_np
        computed_prefill = self.req_states.num_computed_prefill_tokens
        # TODO(woosuk): Simplify this.
        computed_prefill[idx_mapping_np] = np.minimum(
            computed_prefill[idx_mapping_np] + input_batch.num_scheduled_tokens,
            self.req_states.prefill_len.np[idx_mapping_np],
        )

    @torch.inference_mode()
    def propose_draft(
        self,
        input_batch: InputBatch,
        last_hidden_states: torch.Tensor,
        aux_hidden_states: list[torch.Tensor] | None,
        num_sampled: torch.Tensor,
        num_rejected: torch.Tensor,
    ) -> torch.Tensor:
        assert self.speculator is not None
        draft_tokens = self.speculator.propose(
            input_batch,
            last_hidden_states,
            aux_hidden_states,
            num_sampled,
            num_rejected,
            self.req_states.last_sampled_tokens,
            self.req_states.next_prefill_tokens,
            self.sampler.sampling_states.temperature.gpu,
            self.sampler.sampling_states.seeds.gpu,
        )
        return draft_tokens

    @torch.inference_mode()
    def execute_model(
        self,
        scheduler_output: SchedulerOutput,
        intermediate_tensors: Any | None = None,
        dummy_run: bool = False,
        skip_attn_for_dummy_run: bool = False,
    ) -> ModelRunnerOutput | None:
        assert intermediate_tensors is None
        if not dummy_run:
            # Update the request states.
            self.finish_requests(scheduler_output)
            self.free_states(scheduler_output)
            self.add_requests(scheduler_output)
            self.update_requests(scheduler_output)
            self.block_tables.apply_staged_writes()
            if scheduler_output.total_num_scheduled_tokens == 0:
                # No need to run the model.
                empty_output = self.kv_connector.no_forward(scheduler_output)
                return empty_output

        # Get the CUDA graph size. None means no CUDA graph is used.
        cudagraph_size = self.cudagraph_manager.get_cudagraph_size(
            scheduler_output.total_num_scheduled_tokens,
            scheduler_output.num_scheduled_tokens.values(),
        )
        use_cudagraph, num_tokens_after_padding, num_tokens_across_dp = (
            get_cudagraph_and_dp_padding(
                scheduler_output.total_num_scheduled_tokens,
                cudagraph_size,
                self.parallel_config.data_parallel_size,
                self.parallel_config.data_parallel_rank,
            )
        )
        if num_tokens_after_padding == 0:
            # All DP ranks have zero tokens to run.
            empty_output = self.kv_connector.no_forward(scheduler_output)
            return empty_output

        if not dummy_run:
            # Common case.
            # Prepare all the inputs and copy to the input buffers.
            input_batch = self.prepare_inputs(
                scheduler_output,
                num_tokens_after_padding,
            )
            if self.lora_config:
                # Activate LoRA adapters.
                lora_inputs = self.req_states.make_lora_inputs(
                    input_batch.req_ids,
                    input_batch.idx_mapping_np,
                    input_batch.num_scheduled_tokens,
                )
                self._set_active_loras(*lora_inputs)

            if self.supports_mm_inputs:
                # Execute the multimodal encoder.
                mm_embeds, is_mm_embed = self.get_mm_embeddings(
                    scheduler_output.scheduled_encoder_inputs, input_batch
                )
                inputs_embeds = self.encoder_runner.get_inputs_embeds(
                    self.model, input_batch.input_ids, mm_embeds, is_mm_embed
                )
                input_batch.inputs_embeds = inputs_embeds[
                    : input_batch.num_tokens_after_padding
                ]
        else:
            # No actual tokens to run. A dummy run for DP or memory profiling.
            num_reqs = min(num_tokens_after_padding, self.max_num_reqs)
            input_batch = InputBatch.make_dummy(
                num_reqs=num_reqs,
                num_tokens=num_tokens_after_padding,
                input_buffers=self.input_buffers,
                device=self.device,
            )
            if self.uses_mrope:
                input_batch.mrope_positions = self.mrope_states.mrope_positions[
                    :, :num_tokens_after_padding
                ]
            if not skip_attn_for_dummy_run:
                self.prepare_dummy_attn_metadata(input_batch)
            # FIXME(woosuk): Fix warmup for LoRA.

        # Run model.
        if use_cudagraph:
            # Run CUDA graph.
            # NOTE(woosuk): Here, we don't need to pass the input tensors,
            # because they are already copied to the CUDA graph input buffers.
            self.kv_connector.pre_forward(scheduler_output)
            hidden_states = self.cudagraph_manager.run(
                input_batch.num_tokens_after_padding
            )
        else:
            # Run PyTorch model in eager mode.
            positions = input_batch.positions
            if self.uses_mrope:
                assert input_batch.mrope_positions is not None
                positions = input_batch.mrope_positions
            slot_mappings = self.block_tables.compute_slot_mappings(
                input_batch.idx_mapping,
                input_batch.query_start_loc,
                input_batch.positions[: input_batch.num_tokens],
            )
            slot_mappings_by_layer = build_slot_mappings_by_layer(
                slot_mappings, self.kv_cache_config
            )
            with set_forward_context(
                input_batch.attn_metadata,
                self.vllm_config,
                num_tokens=input_batch.num_tokens_after_padding,
                # TODO(woosuk): Support piecewise CUDA graph.
                cudagraph_runtime_mode=CUDAGraphMode.NONE,
                num_tokens_across_dp=num_tokens_across_dp,
                slot_mapping=slot_mappings_by_layer,
            ):
                self.kv_connector.pre_forward(scheduler_output)
                hidden_states = self.model(
                    input_ids=input_batch.input_ids,
                    positions=positions,
                    inputs_embeds=input_batch.inputs_embeds,
                )

        kv_connector_output = self.kv_connector.post_forward(scheduler_output)
        self.execute_model_state = hidden_states, input_batch, kv_connector_output
        return None

    @torch.inference_mode()
    def sample_tokens(
        self,
        grammar_output: GrammarOutput | None,
    ) -> AsyncOutput | ModelRunnerOutput:
        assert self.execute_model_state is not None
        hidden_states, input_batch, kv_connector_output = self.execute_model_state
        self.execute_model_state = None  # type: ignore

        sampler_output, num_sampled, num_rejected = self.sample(
            hidden_states, input_batch, grammar_output
        )
        prompt_logprobs_dict = self.prompt_logprobs_worker.compute_prompt_logprobs(
            self.model.compute_logits,
            hidden_states,
            input_batch,
            self.req_states.prefill_token_ids.gpu,
            self.req_states.num_computed_tokens.gpu,
            self.req_states.prompt_len,
            self.req_states.prefill_len.np,
            self.req_states.num_computed_prefill_tokens,
        )

        # Prepare the model runner output.
        model_runner_output = ModelRunnerOutput(
            req_ids=input_batch.req_ids,
            # NOTE(woosuk): req_id_to_index is unused in this model runner.
            # Only for compatibility with the existing model runner and scheduler.
            req_id_to_index={req_id: i for i, req_id in enumerate(input_batch.req_ids)},
            sampled_token_ids=None,  # type: ignore
            prompt_logprobs_dict=prompt_logprobs_dict,  # type: ignore[arg-type]
            kv_connector_output=kv_connector_output,
        )
        async_output = AsyncOutput(
            model_runner_output=model_runner_output,
            sampler_output=sampler_output,
            num_sampled_tokens=num_sampled,
            copy_stream=self.output_copy_stream,
            copy_event=self.output_copy_event,
        )

        # Postprocess results and update request states.
        # NOTE: This is intentionally done after creating the AsyncOutput,
        # ensuring that `copy_event` is recorded before calling postprocess.
        # This sequencing may slightly reduce latency as async D2H copy does not
        # need to wait for the postprocess to finish.
        self.postprocess(
            input_batch, sampler_output.sampled_token_ids, num_sampled, num_rejected
        )
        if self.do_spec_decode:
            draft_tokens = self.propose_draft(
                input_batch,
                hidden_states,
                None,  # aux_hidden_states
                num_sampled,
                num_rejected,
            )
            self.req_states.draft_tokens[input_batch.idx_mapping] = draft_tokens

        if self.use_async_scheduling:
            return async_output
        return async_output.get_output()