[Misc] Add multipstep chunked-prefill support for FlashInfer (#10467)

csrc/prepare_inputs/advance_step.cu

@@ -95,6 +95,16 @@ __global__ void advance_step_flashinfer_kernel(
     long* input_positions_ptr, int* seq_lens_ptr, long* slot_mapping_ptr,
     int const* block_tables_ptr, int64_t const block_tables_stride,
     int* paged_kv_last_page_len_ptr, int* block_table_bound_ptr) {
+  int const n_pad = num_seqs - num_queries;
+  if (n_pad && blockIdx.x == 0) {
+    // Handle cuda graph padding
+    int const offset = num_queries;
+    for (int i = threadIdx.x; i < n_pad; i += blockDim.x) {
+      input_tokens_ptr[offset + i] = 0;
+      input_positions_ptr[offset + i] = 0;
+      slot_mapping_ptr[offset + i] = -1;
+    }
+  }
   int num_query_blocks = div_ceil(num_queries, num_threads);
 
   if (blockIdx.x < num_query_blocks) {

tests/multi_step/test_correctness_llm.py

@@ -5,6 +5,8 @@ from typing import Optional
 
 import pytest
 
+from tests.kernels.utils import override_backend_env_variable
+
 from ..models.utils import check_logprobs_close, check_outputs_equal
 
 MODELS = [
@@ -19,10 +21,11 @@ NUM_PROMPTS = [10]
 @pytest.mark.parametrize("tp_size", [1])
 @pytest.mark.parametrize("enable_chunked_prefill", [False, True])
 @pytest.mark.parametrize("max_tokens", [5])
-@pytest.mark.parametrize("enforce_eager", [True])
+@pytest.mark.parametrize("enforce_eager", [True, False])
 @pytest.mark.parametrize("num_scheduler_steps", NUM_SCHEDULER_STEPS)
 @pytest.mark.parametrize("num_prompts", NUM_PROMPTS)
 @pytest.mark.parametrize("num_logprobs", [None, 5])
+@pytest.mark.parametrize("attention_backend", ["FLASH_ATTN", "FLASHINFER"])
 def test_multi_step_llm(
     hf_runner,
     vllm_runner,
@@ -36,6 +39,8 @@ def test_multi_step_llm(
     num_scheduler_steps: int,
     num_prompts: int,
     num_logprobs: Optional[int],
+    attention_backend: str,
+    monkeypatch,
 ) -> None:
     """Test vLLM engine with multi-step scheduling via sync LLM Engine.
 
@@ -63,6 +68,7 @@ def test_multi_step_llm(
       num_logprobs: corresponds to the `logprobs` argument to the OpenAI
                     completions endpoint; `None` -> 1 logprob returned.
     """
+    override_backend_env_variable(monkeypatch, attention_backend)
 
     prompts = example_prompts
     if len(prompts) < num_prompts:
@@ -114,6 +120,7 @@ def test_multi_step_llm(
 @pytest.mark.parametrize("num_scheduler_steps", NUM_SCHEDULER_STEPS)
 @pytest.mark.parametrize("num_prompts", NUM_PROMPTS)
 @pytest.mark.parametrize("num_logprobs,num_prompt_logprobs", [(5, 5)])
+@pytest.mark.parametrize("attention_backend", ["FLASH_ATTN"])
 def test_multi_step_llm_w_prompt_logprobs(
     vllm_runner,
     example_prompts,
@@ -126,6 +133,8 @@ def test_multi_step_llm_w_prompt_logprobs(
     num_prompts: int,
     num_logprobs: Optional[int],
     num_prompt_logprobs: Optional[int],
+    attention_backend: str,
+    monkeypatch,
 ) -> None:
     """Test prompt logprobs with multi-step scheduling via sync LLM Engine.
 
@@ -155,6 +164,7 @@ def test_multi_step_llm_w_prompt_logprobs(
                            note that this argument is not supported by the
                            OpenAI completions endpoint.
     """
+    override_backend_env_variable(monkeypatch, attention_backend)
 
     prompts = example_prompts
     if len(prompts) < num_prompts:
@@ -205,6 +215,7 @@ def test_multi_step_llm_w_prompt_logprobs(
 @pytest.mark.parametrize("num_scheduler_steps", NUM_SCHEDULER_STEPS)
 @pytest.mark.parametrize("num_prompts", NUM_PROMPTS)
 @pytest.mark.parametrize("num_logprobs", [None, 5])
+@pytest.mark.parametrize("attention_backend", ["FLASH_ATTN"])
 def test_multi_step_llm_chunked_prefill_prefix_cache(
     vllm_runner,
     example_prompts,
@@ -216,6 +227,8 @@ def test_multi_step_llm_chunked_prefill_prefix_cache(
     num_scheduler_steps: int,
     num_prompts: int,
     num_logprobs: Optional[int],
+    attention_backend: str,
+    monkeypatch,
 ) -> None:
     """Test vLLM engine with multi-step+"single-step chunked prefill"+APC.
 
@@ -278,6 +291,8 @@ def test_multi_step_llm_chunked_prefill_prefix_cache(
     #
     # The Incorrect scheduling behavior - if it occurs - will cause an exception
     # in the model runner resulting from `do_sample=False`.
+    override_backend_env_variable(monkeypatch, attention_backend)
+
     assert len(example_prompts) >= 2
     challenge_prompts = copy.deepcopy(example_prompts)
     challenge_prompts[0] = ('vLLM is a high-throughput and memory-efficient '

vllm/attention/backends/flashinfer.py

@@ -256,7 +256,12 @@ class FlashInferState(AttentionState):
     def begin_forward(self, model_input):
         assert not self._is_graph_capturing
         state = self
-        if model_input.attn_metadata.use_cuda_graph:
+        use_cuda_graph = model_input.attn_metadata.use_cuda_graph
+        is_decode = model_input.attn_metadata.num_prefills == 0
+        # In case of multistep chunked-prefill, there might be prefill requests
+        # scheduled while CUDA graph mode is enabled. We don't run graph in that
+        # case.
+        if use_cuda_graph and is_decode:
             batch_size = model_input.input_tokens.shape[0]
             state = (self.runner.graph_runners[model_input.virtual_engine]
                      [batch_size].attn_state)
@@ -429,10 +434,24 @@ class FlashInferMetadata(AttentionMetadata):
         Update metadata in-place to advance one decode step.
         """
 
-        assert not turn_prefills_into_decodes, \
-            ("Chunked prefill is not supported with flashinfer yet."
-             "turn_prefills_into_decodes is a Multi-Step + Chunked-Prefill "
-             "specific parameter.")
+        if turn_prefills_into_decodes:
+            # When Multi-Step is enabled with Chunked-Prefill, prefills and
+            # decodes are scheduled together. In the first step, all the
+            # prefills turn into decodes. This update reflects that
+            # conversion.
+            assert self.num_decode_tokens + self.num_prefills == num_seqs
+            # Flashinfer doesn't support speculative decoding + chunked-prefill
+            # + multi-step scheduling yet.
+            assert self.decode_query_len == 1
+            self.num_decode_tokens += self.num_prefills
+            self.num_prefills = 0
+            self.num_prefill_tokens = 0
+            self.max_prefill_seq_len = 0
+            self.max_query_len = 1
+
+            self.slot_mapping = self.slot_mapping[:num_seqs]
+        else:
+            assert self.seq_lens_tensor is not None
 
         assert num_seqs > 0
         assert num_queries > 0

vllm/worker/model_runner.py

@@ -5,6 +5,7 @@ import itertools
 import time
 import warnings
 import weakref
+from contextlib import contextmanager
 from dataclasses import dataclass
 from typing import (TYPE_CHECKING, Any, Callable, Dict, List, Optional, Set,
                     Tuple, Type, TypeVar, Union)
@@ -1028,6 +1029,8 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
 
         self.has_inner_state = model_config.has_inner_state
 
+        self.in_profile_run = False
+
         # When using CUDA graph, the input block tables must be padded to
         # max_seq_len_to_capture. However, creating the block table in
         # Python can be expensive. To optimize this, we cache the block table
@@ -1228,11 +1231,22 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
 
         return builder.build()  # type: ignore
 
+    @contextmanager
+    def set_in_profile_run(self):
+        self.in_profile_run = True
+        try:
+            yield
+        finally:
+            self.in_profile_run = False
+
     @torch.inference_mode()
     def profile_run(self) -> None:
+        with self.set_in_profile_run():
             # Enable top-k sampling to reflect the accurate memory usage.
-        sampling_params = SamplingParams(top_p=0.99, top_k=self.vocab_size - 1)
-        max_num_batched_tokens = self.scheduler_config.max_num_batched_tokens
+            sampling_params = \
+                SamplingParams(top_p=0.99, top_k=self.vocab_size - 1)
+            max_num_batched_tokens = \
+                self.scheduler_config.max_num_batched_tokens
             max_num_seqs = self.scheduler_config.max_num_seqs
             # This represents the maximum number of different requests
             # that will have unique loras, an therefore the max amount of memory
@@ -1258,12 +1272,12 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
                         for idx in range(max_num_seqs)
                     ]
 
-        # Profile memory usage with max_num_sequences sequences and the total
-        # number of tokens equal to max_num_batched_tokens.
+            # Profile memory usage with max_num_sequences sequences and the
+            # total number of tokens equal to max_num_batched_tokens.
             seqs: List[SequenceGroupMetadata] = []
-        # Additional GPU memory may be needed for multi-modal encoding, which
-        # needs to be accounted for when calculating the GPU blocks for
-        # vLLM blocker manager.
+            # Additional GPU memory may be needed for multi-modal encoding,
+            # which needs to be accounted for when calculating the GPU blocks
+            # for vLLM blocker manager.
             # To exercise the worst scenario for GPU memory consumption,
             # the number of seqs (batch_size) is chosen to maximize the number
             # of images processed.
@@ -1302,7 +1316,8 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
                     lora_request=dummy_lora_requests_per_seq[group_id]
                     if dummy_lora_requests_per_seq else None,
                     multi_modal_data=dummy_data.multi_modal_data,
-                multi_modal_placeholders=dummy_data.multi_modal_placeholders,
+                    multi_modal_placeholders=dummy_data.
+                    multi_modal_placeholders,
                 )
                 seqs.append(seq)
 
@@ -1324,7 +1339,8 @@ class GPUModelRunnerBase(ModelRunnerBase[TModelInputForGPU]):
                 seqs, finished_requests_ids=finished_requests_ids)
             intermediate_tensors = None
             if not get_pp_group().is_first_rank:
-            intermediate_tensors = self.model.make_empty_intermediate_tensors(
+                intermediate_tensors = \
+                    self.model.make_empty_intermediate_tensors(
                     batch_size=batch_size,
                     dtype=self.model_config.dtype,
                     device=self.device)

vllm/worker/multi_step_model_runner.py

@@ -32,7 +32,7 @@ logger = init_logger(__name__)
 MULTI_STEP_ATTENTION_BACKENDS = [
     "FLASH_ATTN", "ROCM_FLASH", "FLASHINFER", "NO_ATTENTION"
 ]
-MULTI_STEP_CHUNKED_PREFILL_ATTENTION_BACKENDS = ["FLASH_ATTN"]
+MULTI_STEP_CHUNKED_PREFILL_ATTENTION_BACKENDS = ["FLASH_ATTN", "FLASHINFER"]
 
 def _get_supported_attention_backends(chunked_prefill_enabled: bool) \
     -> List[str]: