[Attention] Support multiple attention metadata builders per kv_cache_spec + proper local attention no hybrid kv cache fix (#21588)

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

tests/v1/spec_decode/test_eagle.py

@@ -313,7 +313,8 @@ def test_propose(num_speculative_tokens, backend):
 
     # Mock runner for attention metadata building
     proposer.runner = mock.MagicMock()
-    proposer.runner.attn_metadata_builders = [attn_metadata_builder]
+    proposer.runner.attn_groups.append([mock.MagicMock()])
+    proposer.runner.attn_groups[0][0].metadata_builder = attn_metadata_builder
 
     result = proposer.propose(target_token_ids=target_token_ids,
                               target_positions=target_positions,

tests/v1/worker/test_gpu_model_runner.py

@@ -417,12 +417,12 @@ def test_kv_cache_stride_order(monkeypatch, model_runner):
         return rnd_stride
 
     # Patch the attention backend class and re-trigger the KV cache creation.
-    for attn_backend in model_runner.attn_backends:
+    for attn_group in model_runner._attn_group_iterator():
+        attn_backend = attn_group.backend
         monkeypatch.setattr(attn_backend, "get_kv_cache_stride_order",
                             rnd_stride_order)
 
-    model_runner.attn_backends = []
+    model_runner.attn_groups = []
-    model_runner.attn_metadata_builders = []
     model_runner.initialize_kv_cache(model_runner.kv_cache_config)
 
     # Shape is unchanged, but layout may differ

vllm/attention/backends/abstract.py

@@ -106,6 +106,10 @@ class AttentionBackend(ABC):
                      block_size: int, num_seqs: int, num_queries: int) -> None:
         raise NotImplementedError
 
+    @classmethod
+    def full_cls_name(cls) -> tuple[str, str]:
+        return (cls.__module__, cls.__qualname__)
+
 
 @dataclass
 class AttentionMetadata:

vllm/attention/layer.py

@@ -9,6 +9,7 @@ import torch.nn.functional as F
 
 import vllm.envs as envs
 from vllm.attention import AttentionType
+from vllm.attention.backends.abstract import AttentionBackend
 from vllm.attention.selector import backend_name_to_enum, get_attn_backend
 from vllm.attention.utils.kv_sharing_utils import validate_kv_sharing_target
 from vllm.config import CacheConfig, get_current_vllm_config
@@ -80,6 +81,7 @@ class Attention(nn.Module):
         prefix: str = "",
         attn_type: str = AttentionType.DECODER,
         kv_sharing_target_layer_name: Optional[str] = None,
+        attn_backend: Optional[type[AttentionBackend]] = None,
         **extra_impl_args,
     ) -> None:
         """
@@ -137,15 +139,6 @@ class Attention(nn.Module):
         self.num_kv_heads = num_kv_heads
         self.sliding_window = sliding_window
 
-        # For v1 we have backend agnostic iRoPE (local chunked attention)
-        # we have to store the flag on the layer so gpu model runner can
-        # set KVSpec appropriately (and pop it so it doesnt get passed to
-        # the backends)
-        if envs.VLLM_USE_V1:
-            self.use_irope = extra_impl_args.pop("use_irope", False)
-        else:
-            self.use_irope = extra_impl_args.get("use_irope", False)
-
         quant_method = quant_config.get_quant_method(
             self, prefix=prefix) if quant_config else None
         if quant_method is not None and not isinstance(
@@ -166,18 +159,22 @@ class Attention(nn.Module):
         # During model initialization, the default dtype is set as the model
         # weight and activation dtype.
         dtype = torch.get_default_dtype()
-        attn_backend = get_attn_backend(head_size,
+        if attn_backend is None:
-                                        dtype,
+            self.attn_backend = get_attn_backend(head_size,
-                                        kv_cache_dtype,
+                                                 dtype,
-                                        block_size,
+                                                 kv_cache_dtype,
-                                        is_attention_free,
+                                                 block_size,
-                                        use_mla=use_mla)
+                                                 is_attention_free,
-        impl_cls = attn_backend.get_impl_cls()
+                                                 use_mla=use_mla)
+        else:
+            self.attn_backend = attn_backend
+
+        impl_cls = self.attn_backend.get_impl_cls()
         self.impl = impl_cls(num_heads, head_size, scale, num_kv_heads,
                              alibi_slopes, sliding_window, kv_cache_dtype,
                              logits_soft_cap, attn_type,
                              kv_sharing_target_layer_name, **extra_impl_args)
-        self.backend = backend_name_to_enum(attn_backend.get_name())
+        self.backend = backend_name_to_enum(self.attn_backend.get_name())
         self.dtype = dtype
 
         # For cuda-alike (CUDA and ROCM) and cpu platforms, we control how
@@ -187,7 +184,7 @@ class Attention(nn.Module):
         self.use_direct_call = not current_platform.is_cuda_alike(
         ) and not current_platform.is_cpu()
 
-        self.use_output = attn_backend.accept_output_buffer
+        self.use_output = self.attn_backend.accept_output_buffer
         compilation_config = get_current_vllm_config().compilation_config
         if prefix in compilation_config.static_forward_context:
             raise ValueError(f"Duplicate layer name: {prefix}")
@@ -309,6 +306,9 @@ class Attention(nn.Module):
         if hasattr(self.impl, "process_weights_after_loading"):
             self.impl.process_weights_after_loading(act_dtype)
 
+    def get_attn_backend(self) -> type[AttentionBackend]:
+        return self.attn_backend
+
 
 class MultiHeadAttention(nn.Module):
     """Multi-headed attention without any cache, used for ViT."""

vllm/attention/layers/chunked_local_attention.py

@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import functools
+from typing import List, Optional
+
+import torch
+
+from vllm import envs
+from vllm.attention.backends.abstract import AttentionBackend
+from vllm.attention.selector import get_attn_backend
+from vllm.config import CacheConfig, QuantizationConfig
+from vllm.v1.attention.backends.utils import (
+    CommonAttentionMetadata, make_local_attention_virtual_batches,
+    subclass_attention_backend, subclass_attention_metadata_builder)
+
+from ..layer import Attention
+
+
+@functools.lru_cache
+def create_chunked_local_attention_backend(
+    underlying_attn_backend: AttentionBackend,
+    attention_chunk_size: int,
+    block_size: int,
+) -> type[AttentionBackend]:
+    prefix = f"ChunkedLocalAttention_{attention_chunk_size}_{block_size}_"
+
+    def build_preprocess_fn(cm: CommonAttentionMetadata):
+        return make_local_attention_virtual_batches(attention_chunk_size, cm,
+                                                    block_size)
+
+    # Dynamically create a new attention backend that wraps the
+    # underlying attention backend but applies
+    # `make_local_attention_virtual_batches` before calling `build(...)`
+    builder_cls = subclass_attention_metadata_builder(
+        name_prefix=prefix,
+        builder_cls=underlying_attn_backend.get_builder_cls(),
+        build_preprocess_fn=build_preprocess_fn)
+    attn_backend = subclass_attention_backend(
+        name_prefix=prefix,
+        attention_backend_cls=underlying_attn_backend,
+        builder_cls=builder_cls)
+
+    return attn_backend
+
+
+class ChunkedLocalAttention(Attention):
+
+    def __init__(self,
+                 num_heads: int,
+                 head_size: int,
+                 scale: float,
+                 attention_chunk_size: int,
+                 num_kv_heads: Optional[int] = None,
+                 alibi_slopes: Optional[List[float]] = None,
+                 cache_config: Optional[CacheConfig] = None,
+                 quant_config: Optional[QuantizationConfig] = None,
+                 kv_sharing_target_layer_name: Optional[str] = None,
+                 prefix: str = ""):
+        dtype = torch.get_default_dtype()
+        if cache_config is not None:
+            kv_cache_dtype = cache_config.cache_dtype
+            block_size = cache_config.block_size
+        else:
+            kv_cache_dtype = "auto"
+            block_size = 16
+
+        if envs.VLLM_USE_V1:
+            underlying_attn_backend = get_attn_backend(head_size, dtype,
+                                                       kv_cache_dtype,
+                                                       block_size)
+
+            attn_backend = create_chunked_local_attention_backend(
+                underlying_attn_backend, attention_chunk_size, block_size)
+        else:
+            # in v0 the local attention is handled inside the backends
+            attn_backend = None
+
+        super().__init__(
+            num_heads=num_heads,
+            head_size=head_size,
+            scale=scale,
+            num_kv_heads=num_kv_heads,
+            alibi_slopes=alibi_slopes,
+            cache_config=cache_config,
+            quant_config=quant_config,
+            prefix=prefix,
+            kv_sharing_target_layer_name=kv_sharing_target_layer_name,
+            attn_backend=attn_backend)

vllm/attention/selector.py

@@ -142,7 +142,7 @@ def get_attn_backend(
     dtype: torch.dtype,
     kv_cache_dtype: Optional[str],
     block_size: int,
-    is_attention_free: bool,
+    is_attention_free: bool = False,
     use_mla: bool = False,
 ) -> type[AttentionBackend]:
     """Selects which attention backend to use and lazily imports it."""

vllm/model_executor/models/llama4.py

@@ -25,6 +25,7 @@ from torch import nn
 from transformers import Llama4TextConfig
 
 from vllm.attention import Attention
+from vllm.attention.layers.chunked_local_attention import ChunkedLocalAttention
 from vllm.compilation.decorators import support_torch_compile
 from vllm.config import CacheConfig, VllmConfig
 from vllm.distributed import get_tensor_model_parallel_world_size
@@ -194,17 +195,18 @@ class Llama4Attention(nn.Module):
             is_neox_style=is_neox_style,
         ) if not self.nope else None
 
-        self.attn = Attention(
+        attn_cls = Attention if self.nope else ChunkedLocalAttention
+        self.attn = attn_cls(
             self.num_heads,
             self.head_dim,
             self.scaling,
             num_kv_heads=self.num_kv_heads,
             cache_config=cache_config,
             quant_config=quant_config,
-            per_layer_sliding_window=None,
-            use_irope=not self.nope,
             prefix=f"{prefix}.attn",
-        )
+            **({
+                "attention_chunk_size": config.attention_chunk_size
+            } if not self.nope else {}))
 
     def _get_attn_scale(self, positions: torch.Tensor) -> torch.Tensor:
         floor = torch.floor((positions + 1.0) / self.floor_scale)

vllm/v1/attention/backends/utils.py

@@ -5,12 +5,12 @@ import enum
 import functools
 from abc import abstractmethod
 from dataclasses import dataclass, make_dataclass
-from typing import TYPE_CHECKING, Any, ClassVar, Generic, Optional, TypeVar
+from typing import (TYPE_CHECKING, Any, Callable, ClassVar, Generic, Optional,
+                    TypeVar)
 
 import numpy as np
 import torch
 
-from vllm.attention.layer import Attention
 from vllm.config import VllmConfig, get_layers_from_vllm_config
 from vllm.utils import cdiv
 
@@ -20,6 +20,8 @@ if TYPE_CHECKING:
     from vllm.v1.worker.gpu_input_batch import InputBatch
 
 import vllm.envs as envs
+from vllm.attention.backends.abstract import AttentionBackend
+from vllm.attention.layer import Attention
 from vllm.distributed.kv_transfer.kv_connector.utils import (
     get_kv_connector_cache_layout)
 from vllm.logger import init_logger
@@ -532,6 +534,48 @@ def make_local_attention_virtual_batches(
     )
 
 
+def subclass_attention_metadata_builder(
+    name_prefix: str,
+    builder_cls: type[AttentionMetadataBuilder[M]],
+    build_preprocess_fn: Callable[[CommonAttentionMetadata],
+                                  CommonAttentionMetadata],
+) -> type[AttentionMetadataBuilder[M]]:
+    """
+    Return a new subclass of `builder_cls` whose .build(...) method
+    first calls build_preprocess_fn(common_attn_metadata) on the metadata.
+    """
+    name: str = name_prefix + builder_cls.__name__  # type: ignore
+
+    def build(self,
+              common_prefix_len: int,
+              common_attn_metadata: CommonAttentionMetadata,
+              fast_build: bool = False):
+        return builder_cls.build(self, common_prefix_len,
+                                 build_preprocess_fn(common_attn_metadata),
+                                 fast_build)
+
+    Wrapped = type(
+        name,
+        (builder_cls, ),  # inherit from the original
+        {
+            "build": build,
+        })
+    return Wrapped  # type: ignore
+
+
+def subclass_attention_backend(
+        name_prefix: str, attention_backend_cls: type[AttentionBackend],
+        builder_cls: type[AttentionMetadataBuilder[M]]
+) -> type[AttentionBackend]:
+    """
+    Return a new subclass where `get_builder_cls` returns `builder_cls`.
+    """
+    name: str = name_prefix + attention_backend_cls.__name__  # type: ignore
+
+    return type(name, (attention_backend_cls, ),
+                {"get_builder_cls": lambda: builder_cls})
+
+
 def split_decodes_and_prefills(
     common_attn_metadata: CommonAttentionMetadata,
     decode_threshold: int = 1,

vllm/v1/spec_decode/eagle.py

@@ -158,9 +158,9 @@ class EagleProposer:
         assert self.runner is not None
 
         # FIXME: need to consider multiple kv_cache_groups
-        attn_metadata = self.runner.attn_metadata_builders[
+        attn_metadata = self.runner.attn_groups[0][0].metadata_builder\
-            0].build_for_drafting(common_attn_metadata=common_attn_metadata,
+            .build_for_drafting(common_attn_metadata=common_attn_metadata,
-                                  draft_index=0)
+                                draft_index=0)
 
         # At this moment, we assume all eagle layers belong to the same KV
         # cache group, thus using the same attention metadata.
@@ -349,7 +349,8 @@ class EagleProposer:
         hidden_states: torch.Tensor,
         common_attn_metadata: CommonAttentionMetadata,
     ) -> list[torch.Tensor]:
-        tree_attn_metadata_builder = self.runner.attn_metadata_builders[0]
+        tree_attn_metadata_builder = \
+            self.runner.attn_groups[0][0].metadata_builder
         assert isinstance(tree_attn_metadata_builder,
                           TreeAttentionMetadataBuilder)
 

vllm/v1/worker/cpu_model_runner.py

@@ -53,11 +53,11 @@ class CPUModelRunner(GPUModelRunner):
             raise ValueError("Multiple KVCacheGroups is not"
                              "currently supported with CPU model runner.")
 
-        assert type(
+        assert type(self.attn_groups[0]
-            self.attn_metadata_builders[0]) is TorchSDPAMetadataBuilderV1
+                    [0].metadata_builder) is TorchSDPAMetadataBuilderV1
 
-        self.attn_metadata_builders[0].reorder_batch(self.input_batch,
+        self.attn_groups[0][0].metadata_builder.reorder_batch(
-                                                     scheduler_output)
+            self.input_batch, scheduler_output)
 
     def _postprocess_tenosrs(self) -> None:
         # Note: replace device tensors with cpu tensors

vllm/v1/worker/gpu_model_runner.py

@@ -3,7 +3,10 @@
 
 import dataclasses
 import gc
+import itertools
 import time
+from collections import defaultdict
+from collections.abc import Iterator
 from contextlib import contextmanager
 from typing import TYPE_CHECKING, Any, Optional, Union, cast
 
@@ -14,9 +17,9 @@ import torch.nn as nn
 from tqdm import tqdm
 
 import vllm.envs as envs
-from vllm.attention import AttentionType, get_attn_backend
+from vllm.attention import Attention, AttentionType
 from vllm.attention.backends.abstract import AttentionBackend
-from vllm.attention.layer import Attention
+from vllm.attention.layers.chunked_local_attention import ChunkedLocalAttention
 from vllm.compilation.counter import compilation_counter
 from vllm.config import (CompilationLevel, VllmConfig,
                          get_layers_from_vllm_config, update_config)
@@ -50,7 +53,6 @@ from vllm.v1.attention.backends.mamba_selectors import get_mamba_attn_backend
 from vllm.v1.attention.backends.utils import (
     AttentionCGSupport, AttentionMetadataBuilder, CommonAttentionMetadata,
     make_kv_sharing_fast_prefill_attention_metadata,
-    make_local_attention_virtual_batches,
     reorder_batch_to_split_decodes_and_prefills)
 from vllm.v1.kv_cache_interface import (AttentionSpec,
                                         ChunkedLocalAttentionSpec,
@@ -73,8 +75,8 @@ from vllm.v1.worker.kv_connector_model_runner_mixin import (
 from vllm.v1.worker.lora_model_runner_mixin import LoRAModelRunnerMixin
 
 from ..sample.logits_processor import LogitsProcessorManager
-from .utils import (MultiModalBudget, bind_kv_cache, gather_mm_placeholders,
+from .utils import (AttentionGroup, MultiModalBudget, bind_kv_cache,
-                    initialize_kv_cache_for_kv_sharing,
+                    gather_mm_placeholders, initialize_kv_cache_for_kv_sharing,
                     sanity_check_mm_encoder_outputs, scatter_mm_placeholders)
 
 if TYPE_CHECKING:
@@ -162,8 +164,8 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         # self.model: nn.Module  # Set after load_model
         # Initialize in initialize_kv_cache
         self.kv_caches: list[torch.Tensor] = []
-        self.attn_metadata_builders: list[AttentionMetadataBuilder] = []
+        # indexes: [kv_cache_group_id][attn_group]
-        self.attn_backends: list[type[AttentionBackend]] = []
+        self.attn_groups: list[list[AttentionGroup]] = []
         # self.kv_cache_config: KVCacheConfig
 
         # req_id -> (input_id -> encoder_output)
@@ -830,81 +832,51 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 spec_decode_common_attn_metadata is None:
                 spec_decode_common_attn_metadata = common_attn_metadata
 
-            if isinstance(kv_cache_group_spec.kv_cache_spec,
+            for attn_group in self.attn_groups[kv_cache_group_id]:
-                          ChunkedLocalAttentionSpec):
+                # Prepare for cascade attention if enabled & beneficial.
-                common_attn_metadata = make_local_attention_virtual_batches(
+                common_prefix_len = 0
-                    kv_cache_group_spec.kv_cache_spec.attention_chunk_size,
+                builder = attn_group.metadata_builder
-                    common_attn_metadata, self.cache_config.block_size)
+                if self.cascade_attn_enabled:
+                    common_prefix_len = self._compute_cascade_attn_prefix_len(
+                        num_scheduled_tokens,
+                        scheduler_output.
+                        num_common_prefix_blocks[kv_cache_group_id],
+                        kv_cache_group_spec.kv_cache_spec,
+                        builder,
+                    )
 
-            # Prepare for cascade attention if enabled & beneficial.
+                attn_metadata_i = (builder.build(
-            common_prefix_len = 0
+                    common_prefix_len=common_prefix_len,
-            builder = self.attn_metadata_builders[kv_cache_group_id]
+                    common_attn_metadata=common_attn_metadata,
-            if self.cascade_attn_enabled:
-                common_prefix_len = self._compute_cascade_attn_prefix_len(
-                    num_scheduled_tokens,
-                    scheduler_output.
-                    num_common_prefix_blocks[kv_cache_group_id],
-                    kv_cache_group_spec.kv_cache_spec,
-                    builder,
-                )
-
-            attn_metadata_i = (builder.build(
-                common_prefix_len=common_prefix_len,
-                common_attn_metadata=common_attn_metadata,
-            ))
-
-            fast_prefill_metadata = attn_metadata_i
-            if (self.cache_config.kv_sharing_fast_prefill
-                    and self.kv_sharing_fast_prefill_eligible_layers):
-                # Dynamically create a a dataclass type that inherits
-                # from attention metadata type but includes additional
-                # fields logits_indices_padded and num_logits_indices
-                # which are required for prefill truncation
-                fast_prefill_metadata_type = (
-                    make_kv_sharing_fast_prefill_attention_metadata(
-                        metadata_cls=type(attn_metadata_i), ))
-                fast_prefill_metadata = fast_prefill_metadata_type(
-                    **dataclasses.asdict(attn_metadata_i),
-                    logits_indices_padded=logits_indices_padded,
-                    num_logits_indices=logits_indices.size(0),
-                )
-
-            for layer_name in kv_cache_group_spec.layer_names:
-                if (self.cache_config.kv_sharing_fast_prefill and layer_name
-                        in self.kv_sharing_fast_prefill_eligible_layers):
-                    attn_metadata[layer_name] = fast_prefill_metadata
-                    continue
-
-                attn_metadata[layer_name] = attn_metadata_i
-
-            # Hack for now to fix chunked local attention + no hybrid kv cache
-            # manager we can remove this once
-            # https://github.com/vllm-project/vllm/pull/21588
-            # is merged (i.e. properly handle different attention backends for
-            # the same kv_cache_spec)
-            if self.attention_chunk_size is not None \
-                    and self.scheduler_config.disable_hybrid_kv_cache_manager:
-                if not hasattr(self, "local_attention_layers"):
-                    self.local_attention_layers = []
-                    attn_layers = get_layers_from_vllm_config(
-                        self.vllm_config, Attention)
-                    for layer_name, attn_module in attn_layers.items():
-                        if attn_module.use_irope:
-                            self.local_attention_layers.append(layer_name)
-
-                local_attn_metadata_i = (builder.build(
-                    common_prefix_len=0,
-                    common_attn_metadata=make_local_attention_virtual_batches(
-                        self.attention_chunk_size, common_attn_metadata,
-                        self.cache_config.block_size),
                 ))
 
-                for layer_name in self.local_attention_layers:
+                fast_prefill_metadata = attn_metadata_i
-                    attn_metadata[layer_name] = local_attn_metadata_i
+                if (self.cache_config.kv_sharing_fast_prefill
+                        and self.kv_sharing_fast_prefill_eligible_layers):
+                    # Dynamically create a a dataclass type that inherits
+                    # from attention metadata type but includes additional
+                    # fields logits_indices_padded and num_logits_indices
+                    # which are required for prefill truncation
+                    fast_prefill_metadata_type = (
+                        make_kv_sharing_fast_prefill_attention_metadata(
+                            metadata_cls=type(attn_metadata_i), ))
+                    fast_prefill_metadata = fast_prefill_metadata_type(
+                        **dataclasses.asdict(attn_metadata_i),
+                        logits_indices_padded=logits_indices_padded,
+                        num_logits_indices=logits_indices.size(0),
+                    )
+
+                for layer_name in attn_group.layer_names:
+                    if (self.cache_config.kv_sharing_fast_prefill
+                            and layer_name
+                            in self.kv_sharing_fast_prefill_eligible_layers):
+                        attn_metadata[layer_name] = fast_prefill_metadata
+                        continue
+                    attn_metadata[layer_name] = attn_metadata_i
 
         attention_cuda_graphs = all(
-            b.can_run_in_cudagraph(common_attn_metadata)
+            g.metadata_builder.can_run_in_cudagraph(common_attn_metadata)
-            for b in self.attn_metadata_builders)
+            for g in self._attn_group_iterator())
 
         # Hot-Swap lora model
         if self.lora_config:
@@ -2229,11 +2201,11 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                     block_table[kv_cache_group_id].slot_mapping[:num_tokens],
                     causal=True)
 
-                attn_metadata_i = self.attn_metadata_builders[
+                for attn_group in self.attn_groups[kv_cache_group_id]:
-                    kv_cache_group_id].build_for_cudagraph_capture(
+                    attn_metadata_i = attn_group.metadata_builder\
-                        common_attn_metadata)
+                        .build_for_cudagraph_capture(common_attn_metadata)
-                for layer_name in kv_cache_group_spec.layer_names:
+                    for layer_name in kv_cache_group_spec.layer_names:
-                    attn_metadata[layer_name] = attn_metadata_i
+                        attn_metadata[layer_name] = attn_metadata_i
 
         with self.maybe_dummy_run_with_lora(self.lora_config,
                                             num_scheduled_tokens):
@@ -2565,88 +2537,100 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         logger.info("Graph capturing finished in %.0f secs, took %.2f GiB",
                     elapsed_time, cuda_graph_size / (1 << 30))
 
-    def _initialize_single_attn_backend(
-        self, kv_cache_spec: KVCacheSpec, layer_names: list[str]
-    ) -> tuple[AttentionBackend, AttentionMetadataBuilder]:
-        if isinstance(kv_cache_spec, AttentionSpec):
-            attn_backend_i = get_attn_backend(
-                kv_cache_spec.head_size,
-                self.dtype,
-                kv_cache_spec.dtype,
-                kv_cache_spec.block_size,
-                self.model_config.is_attention_free,
-                use_mla=kv_cache_spec.use_mla,
-            )
-            if attn_backend_i is None:
-                error_msg = (f"Error with get_attn_backend: "
-                             f"{kv_cache_spec.head_size=}, "
-                             f"{self.dtype=}, {kv_cache_spec.dtype=}, "
-                             f"{kv_cache_spec.block_size=}, "
-                             f"{self.model_config.is_attention_free=}, "
-                             f"{kv_cache_spec.use_mla=}")
-                logger.error(error_msg)
-                raise NotImplementedError(
-                    "Non-Attention backend is not supported by V1 "
-                    "GPUModelRunner.")
-        elif isinstance(kv_cache_spec, MambaSpec):
-            attn_backend_i = get_mamba_attn_backend(kv_cache_spec.mamba_type)
-        else:
-            raise ValueError(
-                f"Unknown KV cache spec type: {type(kv_cache_spec)}")
-
-        attn_metadata_builder_i = attn_backend_i.get_builder_cls()(
-            kv_cache_spec,
-            layer_names,
-            self.vllm_config,
-            self.device,
-        )
-
-        if self.full_cuda_graph:
-            if attn_metadata_builder_i.attn_cudagraph_support == \
-                AttentionCGSupport.NEVER:
-                raise ValueError(f"Full CUDAGraph not supported for "
-                                 f"{attn_backend_i.__name__}. Turn off "
-                                 f"CompilationConfig.full_cuda_graph or use a "
-                                 f" different attention backend.")
-            if attn_metadata_builder_i.attn_cudagraph_support == \
-                AttentionCGSupport.PURE_DECODE_ONLY:
-                # Limit the max cudagraph size to the max number of
-                # sequences for pure decode only cudagraph backend,
-                # whose max_query_len is 1.
-                self.cudagraph_batch_sizes = [
-                    size for size in self.cudagraph_batch_sizes
-                    if size <= self.scheduler_config.max_num_seqs
-                ]
-        return attn_backend_i, attn_metadata_builder_i
-
     def initialize_attn_backend(self, kv_cache_config: KVCacheConfig) -> None:
         """
         Initialize the attention backends and attention metadata builders.
         """
-        assert len(self.attn_backends) == 0 and len(
+        assert len(self.attn_groups) == 0, \
-            self.attn_metadata_builders
+            "Attention backends are already initialized"
-        ) == 0, "Attention backends are already initialized"
+        attn_layers = get_layers_from_vllm_config(self.vllm_config, Attention)
-        for i, kv_cache_group_spec in enumerate(
-                kv_cache_config.kv_cache_groups):
-            kv_cache_spec = kv_cache_group_spec.kv_cache_spec
 
-            attn_backend_i, attn_metadata_builder_i = (
+        def get_attn_backends_for_layers(
-                self._initialize_single_attn_backend(
+                layer_names: list[str]
-                    kv_cache_spec, kv_cache_group_spec.layer_names))
+        ) -> dict[type[AttentionBackend], list[str]]:
-            self.attn_backends.append(attn_backend_i)
+            attn_backends = {}
-            self.attn_metadata_builders.append(attn_metadata_builder_i)
+            attn_backend_layers = defaultdict(list)
+            # Dedupe based on full class name; this is a bit safer than using
+            # using the class itself as the key because when we create dynamic
+            # attention backend subclasses (e.g. ChunkedLocalAttention) unless
+            # they are cached correctly, there will be different objects per
+            # layer.
+            for layer_name in layer_names:
+                attn_backend = attn_layers[layer_name].get_attn_backend()
+                key = attn_backend.full_cls_name()
+                attn_backends[key] = attn_backend
+                attn_backend_layers[key].append(layer_name)
+            return {
+                attn_backends[k]: v
+                for k, v in attn_backend_layers.items()
+            }
+
+        def create_attn_groups(
+            attn_backends_map: dict[AttentionBackend, list[str]],
+            kv_cache_spec: KVCacheSpec,
+        ) -> list[AttentionGroup]:
+            attn_groups: list[AttentionGroup] = []
+            for attn_backend, layer_names in attn_backends_map.items():
+                attn_metadata_builder_i = attn_backend.get_builder_cls()(
+                    kv_cache_spec,
+                    layer_names,
+                    self.vllm_config,
+                    self.device,
+                )
+                attn_group = AttentionGroup(attn_backend,
+                                            attn_metadata_builder_i,
+                                            layer_names)
+                attn_groups.append(attn_group)
+
+                if self.full_cuda_graph:
+                    if attn_metadata_builder_i.attn_cudagraph_support == \
+                        AttentionCGSupport.NEVER:
+                        raise ValueError(
+                            f"Full CUDAGraph not supported for "
+                            f"{attn_backend.__name__}. Turn off "
+                            f"CompilationConfig.full_cuda_graph or use a "
+                            f" different attention backend.")
+                    if attn_metadata_builder_i.attn_cudagraph_support == \
+                        AttentionCGSupport.PURE_DECODE_ONLY:
+                        # Limit the max cudagraph size to the max number of
+                        # sequences for pure decode only cudagraph backend,
+                        # whose max_query_len is 1.
+                        self.cudagraph_batch_sizes = [
+                            size for size in self.cudagraph_batch_sizes
+                            if size <= self.scheduler_config.max_num_seqs
+                        ]
+
+            return attn_groups
+
+        for kv_cache_group_spec in kv_cache_config.kv_cache_groups:
+            kv_cache_spec = kv_cache_group_spec.kv_cache_spec
+            if isinstance(kv_cache_spec, AttentionSpec):
+                attn_backends = get_attn_backends_for_layers(
+                    kv_cache_group_spec.layer_names)
+            # TODO(lucas): move `get_mamba_attn_backend` into the mamba
+            # layers like above
+            elif isinstance(kv_cache_spec, MambaSpec):
+                attn_backends = {
+                    get_mamba_attn_backend(kv_cache_spec.mamba_type):
+                    kv_cache_group_spec.layer_names
+                }
+            else:
+                raise ValueError(
+                    f"Unknown KV cache spec type: {type(kv_cache_spec)}")
+
+            self.attn_groups.append(
+                create_attn_groups(attn_backends, kv_cache_spec))
 
         # Calculate reorder batch threshold (if neeeded)
         self.calculate_reorder_batch_threshold()
 
-        if len(self.attn_backends) > 0:
+        if len(self.attn_groups) > 0:
             return
 
         # Check if model is encoder-only
         block_size = self.vllm_config.cache_config.block_size
         use_mla = self.vllm_config.model_config.use_mla
         attn_specs = list[AttentionSpec]()
-        attn_layers = get_layers_from_vllm_config(self.vllm_config, Attention)
         for attn_module in attn_layers.values():
 
             if attn_module.attn_type == AttentionType.ENCODER_ONLY:
@@ -2666,11 +2650,10 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             assert len(attn_specs) == len(attn_layers), \
                 "All or none of the layers are expected to be encoder-only"
 
-            attn_backend, attn_metadata_builder = (
+            attn_backends = get_attn_backends_for_layers(attn_layers.keys())
-                self._initialize_single_attn_backend(attn_specs[0],
+
-                                                     attn_layers.keys()))
+            self.attn_groups.append(
-            self.attn_backends.append(attn_backend)
+                create_attn_groups(attn_backends, attn_specs[0]))
-            self.attn_metadata_builders.append(attn_metadata_builder)
             self.is_encoder_only_model = True
 
     def calculate_reorder_batch_threshold(self) -> None:
@@ -2678,7 +2661,9 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         Check that if any backends reorder batches; that the reordering
         is compatible (e.g., decode threshold is the same)
         """
-        for attn_metadata_builder_i in self.attn_metadata_builders:
+        for group in self._attn_group_iterator():
+            attn_metadata_builder_i = group.metadata_builder
+
             # check that if any backends reorder batches; that the reordering
             # is compatible (e.g., decode threshold is the same)
             reorder_batch_threshold_i = (
@@ -2752,6 +2737,18 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         )), "Some layers are not correctly initialized"
         return kv_cache_raw_tensors
 
+    def _attn_group_iterator(self) -> Iterator[AttentionGroup]:
+        return itertools.chain.from_iterable(self.attn_groups)
+
+    def _kv_cache_spec_attn_group_iterator(
+            self) -> Iterator[tuple[KVCacheSpec, AttentionGroup]]:
+        if not self.kv_cache_config.kv_cache_groups:
+            return
+        for kv_cache_spec_id, attn_groups in enumerate(self.attn_groups):
+            for attn_group in attn_groups:
+                yield self.kv_cache_config.kv_cache_groups[
+                    kv_cache_spec_id].kv_cache_spec, attn_group
+
     def _reshape_kv_cache_tensors(
         self,
         kv_cache_config: KVCacheConfig,
@@ -2770,23 +2767,22 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         """
         kv_caches: dict[str, torch.Tensor] = {}
         has_attn, has_mamba = False, False
-        for i, kv_cache_group_spec in enumerate(
+        for kv_cache_spec, group in self._kv_cache_spec_attn_group_iterator():
-                kv_cache_config.kv_cache_groups):
+            attn_backend = group.backend
-            kv_cache_spec = kv_cache_group_spec.kv_cache_spec
+            for layer_name in group.layer_names:
-            for layer_name in kv_cache_group_spec.layer_names:
                 raw_tensor = kv_cache_raw_tensors[layer_name]
                 assert raw_tensor.numel() % kv_cache_spec.page_size_bytes == 0
                 num_blocks = (raw_tensor.numel() //
                               kv_cache_spec.page_size_bytes)
                 if isinstance(kv_cache_spec, AttentionSpec):
                     has_attn = True
-                    kv_cache_shape = self.attn_backends[i].get_kv_cache_shape(
+                    kv_cache_shape = attn_backend.get_kv_cache_shape(
                         num_blocks, kv_cache_spec.block_size,
                         kv_cache_spec.num_kv_heads, kv_cache_spec.head_size)
                     dtype = kv_cache_spec.dtype
                     try:
-                        kv_cache_stride_order = self.attn_backends[
+                        kv_cache_stride_order = \
-                            i].get_kv_cache_stride_order()
+                            attn_backend.get_kv_cache_stride_order()
                         assert len(kv_cache_stride_order) == len(
                             kv_cache_shape)
                     except (AttributeError, NotImplementedError):
@@ -2850,15 +2846,14 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
             kv_cache_raw_tensors: The KV cache buffer of each layer.
         """
 
-        for i, kv_cache_group_spec in enumerate(
+        for kv_cache_spec, group in self._kv_cache_spec_attn_group_iterator():
-                kv_cache_config.kv_cache_groups):
+            for layer_name in group.layer_names:
-            kv_cache_spec = kv_cache_group_spec.kv_cache_spec
-            for layer_name in kv_cache_group_spec.layer_names:
                 raw_tensor = kv_cache_raw_tensors[layer_name]
                 num_blocks = (raw_tensor.numel() //
                               kv_cache_spec.page_size_bytes)
                 if isinstance(kv_cache_spec, AttentionSpec):
-                    kv_cache_shape = self.attn_backends[i].get_kv_cache_shape(
+
+                    kv_cache_shape = group.backend.get_kv_cache_shape(
                         num_blocks, kv_cache_spec.block_size,
                         kv_cache_spec.num_kv_heads, kv_cache_spec.head_size)
                     if kv_cache_shape[0] != num_blocks or kv_cache_shape[
@@ -2893,6 +2888,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 self.shared_kv_cache_layers,
                 kv_cache_config.kv_cache_groups,
                 kv_caches,
+                self.attn_groups,
             )
             attn_layers = get_layers_from_vllm_config(self.vllm_config,
                                                       Attention)
@@ -2958,9 +2954,9 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 continue
 
             # TODO: Support other attention modules, e.g., cross-attention
+            # TODO(lucas): move the attention specs into the model layers like
+            # the attention backends
             if attn_module.attn_type == AttentionType.DECODER:
-                use_local_attention = (self.attention_chunk_size is not None
-                                       and attn_module.use_irope)
                 if attn_module.sliding_window is not None:
                     kv_cache_spec[layer_name] = SlidingWindowSpec(
                         block_size=block_size,
@@ -2969,10 +2965,8 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                         dtype=self.kv_cache_dtype,
                         sliding_window=attn_module.sliding_window,
                         use_mla=use_mla)
-                    assert not use_local_attention, (
+                elif self.attention_chunk_size is not None \
-                        "attention module can not be with ",
+                        and isinstance(attn_module, ChunkedLocalAttention):
-                        "both local attention and sliding window")
-                elif use_local_attention:
                     kv_cache_spec[layer_name] = ChunkedLocalAttentionSpec(
                         block_size=block_size,
                         num_kv_heads=attn_module.num_kv_heads,
@@ -3043,7 +3037,7 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
 
         # Use the first attention metadata builder
         # to create encoder attention metadata
-        builder = self.attn_metadata_builders[0]
+        builder = self.attn_groups[0][0].metadata_builder
 
         dummy_block_table = torch.zeros((num_reqs, 1),
                                         dtype=torch.int32,

vllm/v1/worker/tpu_model_runner.py

@@ -15,8 +15,9 @@ import torch_xla.distributed.spmd as xs
 import torch_xla.runtime as xr
 
 import vllm.envs as envs
+from vllm.attention import Attention
 from vllm.attention.backends.abstract import AttentionType
-from vllm.attention.layer import Attention
+from vllm.attention.layers.chunked_local_attention import ChunkedLocalAttention
 from vllm.compilation.wrapper import TorchCompileWrapperWithCustomDispatcher
 from vllm.config import (ParallelConfig, VllmConfig,
                          get_layers_from_vllm_config, update_config)
@@ -518,7 +519,7 @@ class TPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                 continue
 
             if attn_module.attn_type == AttentionType.DECODER:
-                if attn_module.use_irope:
+                if isinstance(attn_module, ChunkedLocalAttention):
                     logger.warning_once(
                         "Using irope in Pallas is not supported yet, it "
                         "will fall back to global attention for long context.")

vllm/v1/worker/utils.py

@@ -1,14 +1,17 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 from collections import defaultdict
+from dataclasses import dataclass
 from typing import TYPE_CHECKING, Optional
 
 import torch
 
+from vllm.attention.backends.abstract import AttentionBackend
 from vllm.config import ModelConfig, SchedulerConfig
 from vllm.model_executor.models.interfaces import MultiModalEmbeddings
 from vllm.model_executor.models.utils import extract_layer_index
 from vllm.multimodal.registry import MultiModalRegistry
+from vllm.v1.attention.backends.utils import AttentionMetadataBuilder
 from vllm.v1.core.encoder_cache_manager import compute_encoder_budget
 from vllm.v1.kv_cache_interface import KVCacheGroupSpec
 
@@ -122,6 +125,13 @@ class MultiModalBudget:
         return max_items_per_prompt, max_items_per_batch
 
 
+@dataclass
+class AttentionGroup:
+    backend: type[AttentionBackend]
+    metadata_builder: AttentionMetadataBuilder
+    layer_names: list[str]
+
+
 def sanity_check_mm_encoder_outputs(
     mm_embeddings: MultiModalEmbeddings,
     expected_num_items: int,
@@ -196,6 +206,8 @@ def initialize_kv_cache_for_kv_sharing(
     shared_kv_cache_layers: dict[str, str],
     kv_cache_groups: list[KVCacheGroupSpec],
     kv_caches: dict[str, torch.Tensor],
+    # Optional for now to avoid breaking TPU
+    attn_groups: Optional[list[list[AttentionGroup]]] = None,
 ) -> None:
     """
     Sets up KV cache sharing by reusing the allocated KV caches in `kv_caches`
@@ -225,6 +237,15 @@ def initialize_kv_cache_for_kv_sharing(
         group_idx = layer_to_kv_cache_group_idx[target_layer_name]
         kv_cache_groups[group_idx].layer_names.append(layer_name)
 
+        if attn_groups is not None:
+            assert len(attn_groups[group_idx]) == 1, (
+                "Only one attention group per KV cache group is supported "
+                "for KV-cache sharing for now.")
+            # TODO(lucas): I think in the future the layers that re-use a
+            # KV cache will be in a different attention group so we can
+            # remove this code from here.
+            attn_groups[group_idx][0].layer_names.append(layer_name)
+
 
 def bind_kv_cache(
     kv_caches: dict[str, torch.Tensor],