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[Bugfix][Kernel] Add head size check for attention backend selection (#4944)

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Isotr0py 2024-05-22 03:33:25 +08:00 committed by GitHub
parent 14772eeb8e
commit 99eff67ba9
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2 changed files with 21 additions and 7 deletions
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12
vllm/attention/backends/flash_attn.py
View File

@ -9,11 +9,13 @@ from vllm._C import cache_ops
from vllm.attention.backends.abstract import (AttentionBackend, AttentionImpl,
AttentionMetadata)
_SUPPORTED_HEAD_SIZES = [32, 64, 96, 128, 160, 192, 224, 256]
class FlashAttentionBackend(AttentionBackend):
@staticmethod
def get_supported_head_sizes() -> List[int]:
return [32, 64, 96, 128, 160, 192, 224, 256]
@staticmethod
def get_name() -> str:
return "flash-attn"
@ -237,10 +239,12 @@ class FlashAttentionImpl(AttentionImpl):
# paged KV cache.
raise ValueError(
"Sliding window is not supported in FlashAttention.")
if head_size not in _SUPPORTED_HEAD_SIZES:
support_head_sizes = FlashAttentionBackend.get_supported_head_sizes()
if head_size not in support_head_sizes:
raise ValueError(
f"Head size {head_size} is not supported by FlashAttention. "
f"Supported head sizes are: {_SUPPORTED_HEAD_SIZES}.")
f"Supported head sizes are: {support_head_sizes}.")
def forward(
self,

16
vllm/attention/selector.py
View File

@ -34,11 +34,21 @@ def get_attn_backend(
sliding_window, dtype, kv_cache_dtype,
block_size)
if backend == _Backend.FLASH_ATTN:
logger.info("Using FlashAttention-2 backend.")
from vllm.attention.backends.flash_attn import ( # noqa: F401
FlashAttentionBackend)
return FlashAttentionBackend
elif backend == _Backend.XFORMERS:
# We check it here not in _which_attn_to_use because we cannot know
# the head size until we import FlashAttentionBackend.
supported_head_sizes = FlashAttentionBackend.get_supported_head_sizes()
if head_size in supported_head_sizes:
logger.info("Using FlashAttention-2 backend.")
return FlashAttentionBackend
logger.info(
"Cannot use FlashAttention-2 backend for head size %d. "
"Using XFormers backend instead.", head_size)
backend = _Backend.XFORMERS
if backend == _Backend.XFORMERS:
logger.info("Using XFormers backend.")
from vllm.attention.backends.xformers import ( # noqa: F401
XFormersBackend)