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Align CPU attention KV cache layout hint with physical HND layout #1

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Align CPU attention KV cache layout hint with physical HND layout #1

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7bab0b5
Initial plan
Copilot May 15, 2026
1933152
Fix CPU attention backend KV cache layout hint
Copilot May 15, 2026
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6 changes: 5 additions & 1 deletion tests/kernels/attention/test_cpu_attn.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@

from vllm.platforms import CpuArchEnum, current_platform
from vllm.utils.torch_utils import set_random_seed
from vllm.v1.attention.backends.cpu_attn import _get_attn_isa
from vllm.v1.attention.backends.cpu_attn import CPUAttentionBackend, _get_attn_isa

if not current_platform.is_cpu():
pytest.skip("skipping CPU-only tests", allow_module_level=True)
Expand Down Expand Up @@ -59,6 +59,10 @@ def get_attn_isa(
)


def test_cpu_backend_requires_hnd_kv_cache_layout():
assert CPUAttentionBackend.get_required_kv_cache_layout() == "HND"


# rand number generation takes too much time, cache rand tensors
@functools.lru_cache(maxsize=128, typed=False)
def tensor_cache(
Expand Down
5 changes: 5 additions & 0 deletions vllm/v1/attention/backends/cpu_attn.py
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Expand Up @@ -25,6 +25,7 @@
MultipleOf,
)
from vllm.v1.attention.backends.utils import (
KVCacheLayoutType,
split_decodes_and_prefills,
)
from vllm.v1.kv_cache_interface import AttentionSpec, CrossAttentionSpec
Expand Down Expand Up @@ -94,6 +95,10 @@ def get_kv_cache_shape(
) -> tuple[int, ...]:
return 2, num_blocks, num_kv_heads, block_size, head_size

@classmethod
def get_required_kv_cache_layout(cls) -> "KVCacheLayoutType | None":
return "HND"

@staticmethod
def use_cascade_attention(*args, **kwargs) -> bool:
return False
Expand Down