[BugFix] MLA + V1, illegal memory access and accuracy issues (#14253)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>

tests/v1/worker/test_gpu_input_batch.py

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 
+import inspect
 from typing import Optional
 
 import numpy as np
@@ -9,7 +10,8 @@ import torch
 from vllm.sampling_params import SamplingParams
 from vllm.utils import is_pin_memory_available, make_tensor_with_pad
 from vllm.v1.sample.metadata import SamplingMetadata
-from vllm.v1.worker.gpu_input_batch import CachedRequestState, InputBatch
+from vllm.v1.worker.gpu_input_batch import (BlockTable, CachedRequestState,
+                                            InputBatch)
 
 VOCAB_SIZE = 1024
 NUM_OUTPUT_TOKENS = 20
@@ -20,6 +22,34 @@ CUDA_DEVICES = [
 MAX_NUM_PROMPT_TOKENS = 64
 
 
+def _compare_objs(obj1, obj2):
+    attrs = inspect.getmembers(obj1, lambda a: not (inspect.isroutine(a)))
+    attr_names = set([
+        a[0] for a in attrs
+        if not (a[0].startswith('__') and a[0].endswith('__'))
+    ])
+    for attr_name in attr_names:
+        a = getattr(obj1, attr_name)
+        b = getattr(obj2, attr_name)
+
+        is_same = False
+        if isinstance(a, torch.Tensor):
+            if (a.numel() == 0 or b.numel() == 0):
+                is_same = (a.numel() == 0 and b.numel() == 0)
+            elif torch.allclose(a, b):
+                is_same = True
+        elif isinstance(a, np.ndarray):
+            if np.allclose(a, b):
+                is_same = True
+        elif isinstance(a, (BlockTable, SamplingMetadata)):
+            _compare_objs(a, b)
+            is_same = True  # if we make it here must be same
+        elif a == b:
+            is_same = True
+        assert is_same, f"Attribute {attr_name} is different"\
+            f" in {obj1} and {obj2}: {a} != {b}"
+
+
 def _remove_requests(
         input_batch: InputBatch, batch_size: int,
         reqs: list[CachedRequestState]) -> tuple[set[str], list[int]]:
@@ -254,3 +284,61 @@ def test_sampling_metadata_in_input_batch(device: str, batch_size: int):
         assert torch.allclose(
             expected_sampling_metadata.allowed_token_ids_mask,
             sampling_metadata.allowed_token_ids_mask)
+
+
+@pytest.mark.parametrize("device", CUDA_DEVICES)
+@pytest.mark.parametrize("batch_size", [32])
+@pytest.mark.parametrize("swap_list", [((0, 1), )])
+def test_swap_states_in_input_batch(device: str, batch_size: int,
+                                    swap_list: list):
+    """
+    Tests the logic for managing sampling metadata in the InputBatch.
+
+    This test involves adding a set of requests to the InputBatch,
+    followed by removing a subset of them. Afterward, the batch is compacted,
+    and the `make_sampling_metadata` method is invoked on the batch. The
+    output of `make_sampling_metadata` is then compared against the expected
+    results to ensure correctness.
+    """
+    input_batch: InputBatch = InputBatch(
+        max_num_reqs=batch_size,
+        max_model_len=1024,
+        max_num_blocks_per_req=10,
+        device=torch.device(device),
+        pin_memory=is_pin_memory_available(),
+        vocab_size=1024,
+    )
+    ref_input_batch: InputBatch = InputBatch(
+        max_num_reqs=batch_size,
+        max_model_len=1024,
+        max_num_blocks_per_req=10,
+        device=torch.device(device),
+        pin_memory=is_pin_memory_available(),
+        vocab_size=1024,
+    )
+
+    reqs: list[CachedRequestState] = []
+    req_id_reqs = {}
+    req_id_output_token_ids = {}
+    # Add requests
+    for req_index in range(batch_size):
+        req: CachedRequestState = _construct_cached_request_state(req_index)
+        input_batch.add_request(req, req_index)
+        reqs.append(req)
+        req_id_reqs[req.req_id] = req
+        req_id_output_token_ids[req.req_id] = req.output_token_ids
+
+    reordered_reqs = reqs.copy()
+    for swap_pair in swap_list:
+        reordered_reqs[swap_pair[0]], reordered_reqs[swap_pair[1]] = \
+            reordered_reqs[swap_pair[1]], reordered_reqs[swap_pair[0]]
+        input_batch.swap_states(swap_pair[0], swap_pair[1])
+
+    for req_index in range(batch_size):
+        req = reordered_reqs[req_index]
+        ref_input_batch.add_request(req, req_index)
+
+    input_batch.refresh_sampling_metadata()
+    ref_input_batch.refresh_sampling_metadata()
+
+    _compare_objs(input_batch, ref_input_batch)

vllm/v1/attention/backends/flash_attn.py

@@ -100,8 +100,8 @@ class FlashAttentionMetadataBuilder:
         self.runner = runner
 
     def reorder_batch(self, input_batch: "InputBatch",
-                      scheduler_output: "SchedulerOutput"):
-        pass
+                      scheduler_output: "SchedulerOutput") -> bool:
+        return False
 
     def build(self, num_reqs: int, num_actual_tokens: int, max_query_len: int,
               common_prefix_len: int):

vllm/v1/attention/backends/mla/common.py

@@ -275,17 +275,47 @@ class MLACommonBackend(AttentionBackend):
 
 
 @dataclass
-class MLACommonMetadata:
+class MLACommonPrefillMetadata:
+    """ Prefill Specific Metadata """
+
+    @dataclass
+    class ChunkedContextMetadata:
+        # New for MLA (compared to FlashAttention)
+        # For handling chunked prefill
+        cu_seq_lens: torch.Tensor
+        starts: torch.Tensor
+        seq_tot: list[int]
+        max_seq_lens: list[int]
+        workspace: torch.Tensor
+
+    # Input positions for rotrary embeddings since for MLA the rotary
+    # position embeddings are applied inside the attention backend
+    input_positions: torch.Tensor
+    block_table: torch.Tensor
+    query_start_loc: torch.Tensor
+    max_query_len: int
+    chunked_context: Optional[ChunkedContextMetadata] = None
+
+
+@dataclass
+class MLACommonDecodeMetadata:
+    # Input positions for rotrary embeddings since for MLA the rotary
+    # position embeddings are applied inside the attention backend
+    input_positions: torch.Tensor
+    block_table: torch.Tensor
+    seq_lens: torch.Tensor
+
+
+D = TypeVar("D", bound=MLACommonDecodeMetadata)
+
+
+@dataclass
+class MLACommonMetadata(Generic[D]):
     """Metadata for MLACommon.
 
     NOTE: Please read the comment at the top of the file before trying to
     understand this class
     """
-    # New for MLA (compared to FlashAttention)
-    # Input positions for rotrary embeddings since for MLA the rotary
-    # position embeddings are applied inside the attention backend
-    input_positions: torch.Tensor
-
     # NOTE(sang): Definition of context_len, query_len, and seq_len.
     # |---------- N-1 iteration --------|
     # |---------------- N iteration ---------------------|
@@ -295,30 +325,23 @@ class MLACommonMetadata:
     #                                   |-- query_len ---|
 
     num_actual_tokens: int  # Number of tokens excluding padding.
-    max_query_len: int
     query_start_loc: torch.Tensor
-    max_seq_len: int
-    seq_lens: torch.Tensor
-    block_table: torch.Tensor
     slot_mapping: torch.Tensor
 
+    # New for MLA (compared to FlashAttention)
+    # For handling prefill decode split
+    num_decodes: int
+    num_decode_tokens: int
+    num_prefills: int
+
     # For logging.
     num_input_tokens: int = 0  # Number of tokens including padding.
 
     # The dimension of the attention heads
     head_dim: Optional[int] = None
 
-    # New for MLA (compared to FlashAttention)
-    # For chunked prefill
-    num_decodes: Optional[int] = None
-    num_decode_tokens: Optional[int] = None
-    num_prefills: Optional[int] = None
-    has_context: bool = False
-    context_chunk_cu_seq_lens: Optional[torch.Tensor] = None
-    context_chunk_starts: Optional[torch.Tensor] = None
-    context_chunk_seq_tot: Optional[list[int]] = None
-    context_chunk_max_seq_lens: Optional[list[int]] = None
-    chunked_prefill_workspace: Optional[torch.Tensor] = None
+    decode: Optional[D] = None
+    prefill: Optional[MLACommonPrefillMetadata] = None
 
     def __post_init__(self):
         supported_head_sizes = MLACommonBackend.get_supported_head_sizes()
@@ -329,10 +352,10 @@ class MLACommonMetadata:
                 f"received {self.head_dim}.")
 
 
-T = TypeVar("T", bound=MLACommonMetadata)
+M = TypeVar("M", bound=MLACommonMetadata)
 
 
-class MLACommonMetadataBuilder(Generic[T]):
+class MLACommonMetadataBuilder(Generic[M]):
     """
     NOTE: Please read the comment at the top of the file before trying to
     understand this class
@@ -340,8 +363,9 @@ class MLACommonMetadataBuilder(Generic[T]):
 
     def __init__(self,
                  runner: "GPUModelRunner",
-                 cls: Optional[type[T]] = None):
-        self.cls = cls if cls is not None else MLACommonMetadata
+                 metadata_cls: Optional[type[M]] = None):
+        self.metadata_cls = metadata_cls \
+            if metadata_cls is not None else MLACommonMetadata
         self.runner = runner
         scheduler_config = runner.scheduler_config
         model_config = runner.model_config
@@ -375,7 +399,7 @@ class MLACommonMetadataBuilder(Generic[T]):
             self.page_size = self.runner.block_size
 
     def reorder_batch(self, input_batch: "InputBatch",
-                      scheduler_output: "SchedulerOutput"):
+                      scheduler_output: "SchedulerOutput") -> bool:
         # We now want to reorder the batch so that the "decode" requests are and
         # the front and the "prefill" requests are at the using the least amount
         # swaps possible. (NOTE for now we loosely use "decode" to mean requests
@@ -413,6 +437,7 @@ class MLACommonMetadataBuilder(Generic[T]):
         num_decodes = len(decodes)
         num_prefills = len(prefills)
         first_prefill = 0
+        modified_batch = False
 
         for i in range(1, min(num_decodes, num_prefills) + 1):
             # If the decode is at the "back" of the batch, i, we can swap it
@@ -421,6 +446,7 @@ class MLACommonMetadataBuilder(Generic[T]):
                 input_batch.swap_states(prefills[first_prefill],
                                         decodes[num_decodes - i])
                 first_prefill += 1
+                modified_batch = True
             else:
                 break
 
@@ -432,10 +458,21 @@ class MLACommonMetadataBuilder(Generic[T]):
         self._num_decode_tokens = num_decode_tokens
         self._num_prefill_tokens = num_prefill_tokens
 
+        return modified_batch
+
+    def _build_decode(self, input_positions: torch.Tensor,
+                      block_table: torch.Tensor, seq_lens: torch.Tensor):
+        return MLACommonDecodeMetadata(
+            input_positions=input_positions,
+            block_table=block_table,
+            seq_lens=seq_lens,
+        )
+
     def build(self, num_reqs: int, num_actual_tokens: int, max_query_len: int,
-              common_prefix_len: int) -> T:
+              common_prefix_len: int) -> M:
+        assert self._num_decodes + self._num_prefills == num_reqs
+
         device = self.runner.device
-        max_seq_len = self.runner.seq_lens_np[:num_reqs].max()
         query_start_loc = self.runner.query_start_loc_cpu[:num_reqs + 1].to(
             device, non_blocking=True)
         seq_lens = self.runner.seq_lens_cpu[:num_reqs].to(device,
@@ -447,85 +484,103 @@ class MLACommonMetadataBuilder(Generic[T]):
         input_positions = self.runner.positions_cpu[:num_actual_tokens].to(
             device, non_blocking=True).long()
 
-        context_chunk_cu_seq_lens = None
-        context_chunk_starts = None
-        context_chunk_seq_tot = None
-        context_chunk_max_seq_lens = None
+        prefill_metadata = None
+        if self._num_prefills > 0:
+            reqs_start = self._num_decodes  # prefill_start
+            tokens_start = self._num_decode_tokens
 
-        num_computed_tokens_cpu_tensor = \
-            self.runner.input_batch.num_computed_tokens_cpu_tensor[:num_reqs]
-        context_lens_tensor = \
-            num_computed_tokens_cpu_tensor.to(device, non_blocking=True)
+            context_lens_cpu = self.runner.input_batch.\
+                num_computed_tokens_cpu_tensor[reqs_start:num_reqs]
+            context_lens = context_lens_cpu.to(device, non_blocking=True)
 
-        if self.chunked_prefill_enabled and self._num_prefills > 0 \
-            and context_lens_tensor[self._num_decodes:].max() > 0:
-            # NOTE: it is recommend you read the `Chunked Prefill` section in
-            # the comment at the top of the file before trying to understand
-            # the following code
+            chunked_context_metadata = None
+            if self.chunked_prefill_enabled and self._num_prefills > 0 \
+                and context_lens.max() > 0:
+                # NOTE: it is recommend you read the `Chunked Prefill` section
+                # in the comment at the top of the file before trying to
+                # understand the following code
 
-            self.has_context = True
+                num_prefills_with_context = (context_lens > 0).sum().item()
 
-            num_prefills_with_context = \
-                (context_lens_tensor[self._num_decodes:] > 0).sum().item()
+                # currently we allocate an equal amount of workspace for each
+                # prefill in the batch, we could probably use a more advanced
+                # algorithm here and allocate more workspace to prefills with
+                # longer context lengths
+                max_context_chunk = \
+                    self.chunked_prefill_workspace_size \
+                        // num_prefills_with_context
 
-            # currently we allocate an equal amount of workspace for each
-            # prefill in the batch, we could probably use a more advanced
-            # algorithm here and allocate more workspace to prefills with
-            # longer context lengths
-            max_context_chunk = \
-                self.chunked_prefill_workspace_size // num_prefills_with_context
+                # align max_context_chunk to page_size by rounding down,
+                # currently the `gather_cache` kernel cannot handle
+                # `context_chunk_starts` that are not aligned to page_size
+                max_context_chunk = round_down(max_context_chunk,
+                                               self.page_size)
 
-            # align max_context_chunk to page_size by rounding down,
-            # currently the `gather_cache` kernel cannot handle
-            # `context_chunk_starts` that are not aligned to page_size
-            max_context_chunk = round_down(max_context_chunk, self.page_size)
-            assert max_context_chunk > 0
-            num_chunks = cdiv(context_lens_tensor.max(), max_context_chunk)
+                assert max_context_chunk > 0
+                num_chunks = cdiv(context_lens.max(), max_context_chunk)
 
-            # if `max_context_chunk = 256`, `num_chunks = 3`, and
-            #   `num_prefills_with_context = 4`, create a tensor that looks like
-            #  [[0, 0, 0, 0], [256, 256, 256, 256], [512, 512, 512, 512]]
-            context_chunk_starts = \
-                torch.arange(num_chunks, device=device, dtype=torch.int32) \
-                .unsqueeze(1).expand(-1, self._num_prefills) \
-                * max_context_chunk
-            chunk_ends = torch.min(context_lens_tensor[self._num_decodes:] \
-                .unsqueeze(0), context_chunk_starts + max_context_chunk)
-            chunk_seq_lens = (chunk_ends - context_chunk_starts).clamp(min=0)
-            _context_chunk_cu_seq_lens = chunk_seq_lens.cumsum(dim=1).to(
-                torch.int32)
-            zero = torch.zeros(num_chunks, dtype=torch.int32, device=device) \
-                .unsqueeze(-1)
-            context_chunk_cu_seq_lens = \
-                torch.cat([zero, _context_chunk_cu_seq_lens], dim=1)
-            context_chunk_max_seq_lens = \
-                chunk_seq_lens.max(dim=1).values.tolist()
-            context_chunk_seq_tot = chunk_seq_lens.sum(dim=1).tolist()
-            assert max(context_chunk_seq_tot) <= \
-                self.chunked_prefill_workspace_size
+                # if `max_context_chunk = 256`, `num_chunks = 3`, and
+                #   `num_prefills_with_context = 4`, create a tensor that looks
+                # like
+                #  [[0, 0, 0, 0], [256, 256, 256, 256], [512, 512, 512, 512]]
+                chunk_starts = \
+                    torch.arange(num_chunks, device=device, dtype=torch.int32) \
+                    .unsqueeze(1).expand(-1, self._num_prefills) \
+                    * max_context_chunk
+                chunk_ends = torch.min(context_lens.unsqueeze(0),
+                                       chunk_starts + max_context_chunk)
+                chunk_seq_lens = (chunk_ends - chunk_starts).clamp(min=0)
+                _chunk_cu_seq_lens = chunk_seq_lens.cumsum(dim=1).to(
+                    torch.int32)
+                zero = torch.zeros(num_chunks,
+                                   dtype=torch.int32,
+                                   device=device).unsqueeze(-1)
 
-        return self.cls(
-            input_positions=input_positions,
+                chunked_context_metadata = \
+                    MLACommonPrefillMetadata.ChunkedContextMetadata(
+                    cu_seq_lens=torch.cat(
+                        [zero, _chunk_cu_seq_lens], dim=1),
+                    starts=chunk_starts,
+                    seq_tot=chunk_seq_lens.sum(dim=1).tolist(),
+                    max_seq_lens=chunk_seq_lens.max(dim=1).values.tolist(),
+                    workspace=self.chunked_prefill_workspace,
+                )
+
+                assert max(chunked_context_metadata.max_seq_lens) <= \
+                    self.chunked_prefill_workspace_size
+
+            prefill_metadata = MLACommonPrefillMetadata(
+                input_positions=input_positions[tokens_start:],
+                block_table=block_table[reqs_start:, ...],
+                query_start_loc=query_start_loc[reqs_start:] -
+                query_start_loc[reqs_start],
+                max_query_len=seq_lens[reqs_start:].max().item(),
+                chunked_context=chunked_context_metadata,
+            )
+
+        decode_metadata = None
+        if self._num_decodes > 0:
+            decode_metadata = self._build_decode(
+                input_positions=input_positions[:self._num_decode_tokens],
+                block_table=block_table[:self._num_decodes, ...],
+                seq_lens=seq_lens[:self._num_decodes],
+            )
+
+        return self.metadata_cls(
             num_actual_tokens=num_actual_tokens,
-            max_query_len=max_query_len,
             query_start_loc=query_start_loc,
-            max_seq_len=max_seq_len,
-            seq_lens=seq_lens,
-            block_table=block_table,
             slot_mapping=slot_mapping,
             head_dim=self.runner.model_config.get_head_size(),
             # MLACommonMetadata Chunk prefill specific
             num_decodes=self._num_decodes,
             num_decode_tokens=self._num_decode_tokens,
             num_prefills=self._num_prefills,
-            context_chunk_cu_seq_lens=context_chunk_cu_seq_lens,
-            context_chunk_starts=context_chunk_starts,
-            context_chunk_seq_tot=context_chunk_seq_tot,
-            context_chunk_max_seq_lens=context_chunk_max_seq_lens,
+            prefill=prefill_metadata,
+            decode=decode_metadata,
         )
 
 
-class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
+class MLACommonImpl(MLAAttentionImpl[M], Generic[M]):
     """
     NOTE: Please read the comment at the top of the file before trying to
     understand this class
@@ -798,28 +853,24 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
         kv_c_and_k_pe_cache: torch.Tensor,
         attn_metadata: MLACommonMetadata,
     ):
-        assert attn_metadata.num_prefills is not None
-        assert attn_metadata.context_chunk_seq_tot is not None
-        assert attn_metadata.context_chunk_cu_seq_lens is not None
-        assert attn_metadata.context_chunk_starts is not None
-        assert attn_metadata.context_chunk_max_seq_lens is not None
+        assert attn_metadata.prefill is not None
+        prefill_metadata = attn_metadata.prefill
+        assert prefill_metadata.chunked_context is not None
 
         output = None
-        iters = len(attn_metadata.context_chunk_seq_tot)
-
-        assert attn_metadata.chunked_prefill_workspace is not None
-        workspace = attn_metadata.chunked_prefill_workspace
+        iters = len(prefill_metadata.chunked_context.seq_tot)
+        workspace = prefill_metadata.chunked_context.workspace
 
         for i in range(iters):
-            toks = attn_metadata.context_chunk_seq_tot[i]
+            toks = prefill_metadata.chunked_context.seq_tot[i]
 
             ops.gather_cache(
                 src_cache=kv_c_and_k_pe_cache,
                 dst=workspace,
-                block_table=attn_metadata.block_table,
-                cu_seq_lens=attn_metadata.context_chunk_cu_seq_lens[i],
+                block_table=prefill_metadata.block_table,
+                cu_seq_lens=prefill_metadata.chunked_context.cu_seq_lens[i],
                 batch_size=attn_metadata.num_prefills,
-                seq_starts=attn_metadata.context_chunk_starts[i],
+                seq_starts=prefill_metadata.chunked_context.starts[i],
             )
 
             kv_c_normed = workspace[:toks]\
@@ -845,10 +896,10 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
                 q=q,
                 k=k,
                 v=v_padded,
-                cu_seqlens_q=attn_metadata.query_start_loc,
-                cu_seqlens_k=attn_metadata.context_chunk_cu_seq_lens[i],
-                max_seqlen_q=attn_metadata.max_query_len,
-                max_seqlen_k=attn_metadata.context_chunk_max_seq_lens[i],
+                cu_seqlens_q=prefill_metadata.query_start_loc,
+                cu_seqlens_k=prefill_metadata.chunked_context.cu_seq_lens[i],
+                max_seqlen_q=prefill_metadata.max_query_len,
+                max_seqlen_k=prefill_metadata.chunked_context.max_seq_lens[i],
                 softmax_scale=self.scale,
                 causal=False,  # Context is unmasked
                 return_softmax_lse=True,
@@ -881,7 +932,9 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
         kv_c_and_k_pe_cache: torch.Tensor,
         attn_metadata: MLACommonMetadata,
     ) -> torch.Tensor:
-        has_context = attn_metadata.has_context
+        assert attn_metadata.prefill is not None
+
+        has_context = attn_metadata.prefill.chunked_context is not None
         kv_nope = self.kv_b_proj(kv_c_normed)[0].view(\
             -1, self.num_heads, self.qk_nope_head_dim + self.v_head_dim)
         k_nope, v = kv_nope\
@@ -898,10 +951,10 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
             q=q,
             k=k,
             v=v_padded,
-            cu_seqlens_q=attn_metadata.query_start_loc,
-            cu_seqlens_k=attn_metadata.query_start_loc,
-            max_seqlen_q=attn_metadata.max_query_len,
-            max_seqlen_k=attn_metadata.max_seq_len,
+            cu_seqlens_q=attn_metadata.prefill.query_start_loc,
+            cu_seqlens_k=attn_metadata.prefill.query_start_loc,
+            max_seqlen_q=attn_metadata.prefill.max_query_len,
+            max_seqlen_k=attn_metadata.prefill.max_query_len,
             softmax_scale=self.scale,
             causal=True,
             return_softmax_lse=has_context,
@@ -934,7 +987,7 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
         q_nope: torch.Tensor,
         q_pe: torch.Tensor,
         kv_c_and_k_pe_cache: torch.Tensor,
-        attn_metadata: T,
+        attn_metadata: M,
     ) -> torch.Tensor:
         raise NotImplementedError
 
@@ -945,7 +998,7 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
         k_c_normed: torch.Tensor,  # key in unified attn
         k_pe: torch.Tensor,  # value in unified attn
         kv_cache: torch.Tensor,
-        attn_metadata: T,
+        attn_metadata: M,
         output: Optional[torch.Tensor] = None,
     ) -> torch.Tensor:
 
@@ -966,7 +1019,6 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
 
         # Restore head dim (for rotary embedding)
         k_pe = k_pe.unsqueeze(1)
-        assert hasattr(attn_metadata, "input_positions")
 
         assert attn_metadata.num_decodes is not None and \
             attn_metadata.num_prefills is not None and \
@@ -978,28 +1030,27 @@ class MLACommonImpl(MLAAttentionImpl[T], Generic[T]):
 
         decode_hs_or_q_c = hidden_states_or_q_c[:num_decode_tokens]
         decode_k_pe = k_pe[:num_decode_tokens]
-        decode_input_positions = \
-            attn_metadata.input_positions[:num_decode_tokens]
 
         prefill_hs_or_q_c = hidden_states_or_q_c[num_decode_tokens:]
         prefill_k_pe = k_pe[num_decode_tokens:]
-        prefill_input_positions = \
-            attn_metadata.input_positions[num_decode_tokens:]
         prefill_k_c_normed = k_c_normed[num_decode_tokens:]
 
         if has_decode:
+            assert attn_metadata.decode is not None
             decode_q_nope = self._q_proj_and_k_up_proj(decode_hs_or_q_c)
             decode_q_pe = torch.matmul(decode_hs_or_q_c, self.W_QR)\
                 .view(-1, self.num_heads, self.qk_rope_head_dim)
             decode_q_pe[...], decode_k_pe[...] = self.rotary_emb(
-                decode_input_positions, decode_q_pe, decode_k_pe)
+                attn_metadata.decode.input_positions, decode_q_pe, decode_k_pe)
 
         if has_prefill:
+            assert attn_metadata.prefill is not None
             prefill_q = self.q_proj(prefill_hs_or_q_c)[0]\
                 .view(-1, self.num_heads, self.qk_head_dim)
             prefill_q_pe = prefill_q[..., self.qk_nope_head_dim:]
             prefill_q_pe[...], prefill_k_pe[...] = self.rotary_emb(
-                prefill_input_positions, prefill_q_pe, prefill_k_pe)
+                attn_metadata.prefill.input_positions, prefill_q_pe,
+                prefill_k_pe)
 
         # write the latent and rope to kv cache
         if kv_cache.numel() > 0:

vllm/v1/attention/backends/mla/flashmla.py

@@ -11,6 +11,7 @@ from vllm.attention.ops.flashmla import (flash_mla_with_kvcache,
                                          is_flashmla_supported)
 from vllm.logger import init_logger
 from vllm.v1.attention.backends.mla.common import (MLACommonBackend,
+                                                   MLACommonDecodeMetadata,
                                                    MLACommonImpl,
                                                    MLACommonMetadata,
                                                    MLACommonMetadataBuilder)
@@ -38,34 +39,41 @@ class FlashMLABackend(MLACommonBackend):
 
 
 @dataclass
-class FlashMLAMetadata(MLACommonMetadata):
-    decode_tile_scheduler_metadata: Optional[tuple[torch.Tensor,
-                                                   torch.Tensor]] = None
-    decode_num_splits: Optional[torch.Tensor] = None
+class FlashMLADecodeMetadata(MLACommonDecodeMetadata):
+    tile_scheduler_metadata: tuple[torch.Tensor, torch.Tensor]
+    num_splits: torch.Tensor
+
+
+@dataclass
+class FlashMLAMetadata(MLACommonMetadata[FlashMLADecodeMetadata]):
+    pass
 
 
 class FlashMLAMetadataBuilder(MLACommonMetadataBuilder[FlashMLAMetadata]):
 
     def __init__(self, runner):
-        super().__init__(runner, cls=FlashMLAMetadata)
+        super().__init__(runner)
 
         self.num_q_heads = self.runner.model_config.get_num_attention_heads(
             self.runner.parallel_config)
 
-    def build(self, num_reqs: int, num_actual_tokens: int, max_query_len: int,
-              common_prefix_len: int):
-        m = super().build(num_reqs, num_actual_tokens, max_query_len,
-                          common_prefix_len)
+    def _build_decode(self, input_positions: torch.Tensor,
+                      block_table: torch.Tensor,
+                      seq_lens: torch.Tensor) -> FlashMLADecodeMetadata:
+        tile_scheduler_metadata, num_splits = \
+            get_mla_metadata(
+            seq_lens,
+            self.num_q_heads,
+            1, # MQA for the decode path
+        )
 
-        if m.num_decode_tokens is not None and m.num_decode_tokens > 0:
-            m.decode_tile_scheduler_metadata, m.decode_num_splits = \
-                get_mla_metadata(
-                m.seq_lens[:m.num_decode_tokens],
-                self.num_q_heads,
-                1, # MQA for the decode path
-            )
-
-        return m
+        return FlashMLADecodeMetadata(
+            input_positions=input_positions,
+            block_table=block_table,
+            seq_lens=seq_lens,
+            tile_scheduler_metadata=tile_scheduler_metadata,
+            num_splits=num_splits,
+        )
 
 
 class FlashMLAImpl(MLACommonImpl[FlashMLAMetadata]):
@@ -115,6 +123,8 @@ class FlashMLAImpl(MLACommonImpl[FlashMLAMetadata]):
         attn_metadata: FlashMLAMetadata,
     ) -> torch.Tensor:
         assert kv_c_and_k_pe_cache.numel() > 0
+        assert attn_metadata.decode is not None
+
         if self.kv_cache_dtype.startswith("fp8"):
             raise NotImplementedError("FP8 FlashMLA not yet supported")
 
@@ -124,14 +134,12 @@ class FlashMLAImpl(MLACommonImpl[FlashMLAMetadata]):
         o, _ = flash_mla_with_kvcache(
             q=q,
             k_cache=kv_c_and_k_pe_cache.unsqueeze(-2),  # Add head dim of 1
-            block_table=attn_metadata.block_table[:attn_metadata.num_decodes,
-                                                  ...],
-            cache_seqlens=attn_metadata.seq_lens[:attn_metadata.
-                                                 num_decode_tokens],
+            block_table=attn_metadata.decode.block_table,
+            cache_seqlens=attn_metadata.decode.seq_lens,
             head_dim_v=self.kv_lora_rank,
-            tile_scheduler_metadata=attn_metadata.
-            decode_tile_scheduler_metadata,
-            num_splits=attn_metadata.decode_num_splits,
+            tile_scheduler_metadata=attn_metadata.decode.
+            tile_scheduler_metadata,
+            num_splits=attn_metadata.decode.num_splits,
             softmax_scale=self.scale,
             causal=True,
         )

vllm/v1/attention/backends/mla/triton_mla.py

@@ -69,6 +69,8 @@ class TritonMLAImpl(MLACommonImpl[MLACommonMetadata]):
         attn_metadata: MLACommonMetadata,
     ) -> torch.Tensor:
         assert kv_c_and_k_pe_cache.numel() > 0
+        assert attn_metadata.decode is not None
+
         if self.kv_cache_dtype.startswith("fp8"):
             raise NotImplementedError("FP8 Triton MLA not yet supported")
 
@@ -104,7 +106,8 @@ class TritonMLAImpl(MLACommonImpl[MLACommonMetadata]):
 
         # Run MQA
         decode_attention_fwd(q, kv_c_and_k_pe_cache, kv_c_cache, o,
-                             attn_metadata.block_table, attn_metadata.seq_lens,
-                             attn_logits, num_kv_splits, self.scale, PAGE_SIZE)
+                             attn_metadata.decode.block_table,
+                             attn_metadata.decode.seq_lens, attn_logits,
+                             num_kv_splits, self.scale, PAGE_SIZE)
 
         return self._v_up_proj_and_o_proj(o)

vllm/v1/worker/gpu_input_batch.py

@@ -383,8 +383,6 @@ class InputBatch:
             self.req_id_to_index[old_id_i2], self.req_id_to_index[old_id_i1]
         self.num_tokens[i1], self.num_tokens[i2] =\
             self.num_tokens[i2], self.num_tokens[i1]
-        self.token_ids_cpu[i1, ...], self.token_ids_cpu[i2, ...], =\
-            self.token_ids_cpu[i2, ...], self.token_ids_cpu[i1, ...]
         self.num_tokens_no_spec[i1], self.num_tokens_no_spec[i2] =\
             self.num_tokens_no_spec[i2], self.num_tokens_no_spec[i1]
         self.num_prompt_tokens[i1], self.num_prompt_tokens[i2] =\
@@ -406,24 +404,47 @@ class InputBatch:
         self.min_p_cpu[i1], self.min_p_cpu[i2] =\
             self.min_p_cpu[i2], self.min_p_cpu[i1]
 
+        # NOTE: the following is unsafe
+        # self.token_ids_cpu[i1, ...], self.token_ids_cpu[i2, ...], =\
+        #     self.token_ids_cpu[i2, ...], self.token_ids_cpu[i1, ...]
+        # instead, we need to temporiarily copy the data for one of the indices
+        # TODO(lucas): optimize this by only copying valid indices
+        tmp = self.token_ids_cpu[i1, ...].copy()
+        self.token_ids_cpu[i1, ...] = self.token_ids_cpu[i2, ...]
+        self.token_ids_cpu[i2, ...] = tmp
+
         g1 = self.generators.get(i1)
         g2 = self.generators.get(i2)
         if g1 is not None:
             self.generators[i2] = g1
+        else:
+            self.generators.pop(i2, None)
         if g2 is not None:
             self.generators[i1] = g2
+        else:
+            self.generators.pop(i1, None)
 
         t1 = self.min_tokens.get(i1)
         t2 = self.min_tokens.get(i2)
         if t1 is not None:
             self.min_tokens[i2] = t1
+        else:
+            self.min_tokens.pop(i2, None)
         if t2 is not None:
             self.min_tokens[i1] = t2
+        else:
+            self.min_tokens.pop(i1, None)
 
         self.request_lora_mapping[i1], self.request_lora_mapping[i2] =\
             self.request_lora_mapping[i2], self.request_lora_mapping[i1]
         self.logit_bias[i1], self.logit_bias[i2] =\
             self.logit_bias[i2], self.logit_bias[i1]
+
+        if self.allowed_token_ids_mask_cpu_tensor is not None:
+            self.allowed_token_ids_mask_cpu_tensor[i1], \
+                self.allowed_token_ids_mask_cpu_tensor[i2] =\
+                self.allowed_token_ids_mask_cpu_tensor[i2], \
+                    self.allowed_token_ids_mask_cpu_tensor[i1]
         self.block_table.swap_row(i1, i2)
 
     def condense(self, empty_req_indices: list[int]) -> None:

vllm/v1/worker/gpu_model_runner.py

@@ -456,8 +456,10 @@ class GPUModelRunner(LoRAModelRunnerMixin):
         # Some attention backends (namely MLA) may want to separate requests
         # based on if the attention computation will be compute-bound or
         # memory-bound. This gives them a hook to do that.
-        self.attn_metadata_builder.reorder_batch(self.input_batch,
-                                                 scheduler_output)
+        modified_batch = self.attn_metadata_builder.reorder_batch(
+            self.input_batch, scheduler_output)
+        if modified_batch:
+            self.input_batch.refresh_sampling_metadata()
 
         # OPTIMIZATION: Start copying the block table first.
         # This way, we can overlap the copy with the following CPU operations.