178 lines
6.0 KiB
Python
178 lines
6.0 KiB
Python
# SPDX-License-Identifier: Apache-2.0
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# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
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from typing import Any
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from vllm.logger import init_logger
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from vllm.platforms import current_platform
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logger = init_logger(__name__)
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# Track whether upstream flash-attn is available on ROCm.
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# Set during module initialization and never modified afterwards.
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# This module-level flag avoids repeated import attempts and ensures
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# consistent behavior (similar to IS_AITER_FOUND in _aiter_ops.py).
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_ROCM_FLASH_ATTN_AVAILABLE = False
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if current_platform.is_cuda():
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from vllm._custom_ops import reshape_and_cache_flash
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# from vllm.vllm_flash_attn import ( # type: ignore[attr-defined]
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# flash_attn_varlen_func,
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# get_scheduler_metadata,
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# )
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from ixformer.contrib.vllm_flash_attn import flash_attn_varlen_func, flash_attn_with_kvcache
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elif current_platform.is_xpu():
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from vllm import _custom_ops as ops
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from vllm._xpu_ops import xpu_ops
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reshape_and_cache_flash = ops.reshape_and_cache_flash
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flash_attn_varlen_func = xpu_ops.flash_attn_varlen_func # type: ignore[assignment]
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get_scheduler_metadata = xpu_ops.get_scheduler_metadata # type: ignore[assignment]
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elif current_platform.is_rocm():
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try:
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from flash_attn import flash_attn_varlen_func # type: ignore[no-redef]
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# Mark that upstream flash-attn is available on ROCm
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_ROCM_FLASH_ATTN_AVAILABLE = True
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except ImportError:
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def flash_attn_varlen_func(*args: Any, **kwargs: Any) -> Any: # type: ignore[no-redef,misc]
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raise ImportError(
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"ROCm platform requires upstream flash-attn "
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"to be installed. Please install flash-attn first."
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)
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# ROCm doesn't use scheduler metadata (FA3 feature), provide stub
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def get_scheduler_metadata(*args: Any, **kwargs: Any) -> None: # type: ignore[misc]
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return None
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# ROCm uses the C++ custom op for reshape_and_cache
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from vllm import _custom_ops as ops
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reshape_and_cache_flash = ops.reshape_and_cache_flash
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def get_flash_attn_version(requires_alibi: bool = False) -> int | None:
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# import here to avoid circular dependencies
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from vllm.platforms import current_platform
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return 3
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if current_platform.is_xpu():
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return 2
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if current_platform.is_rocm():
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# ROCm doesn't use vllm_flash_attn; return None to skip fa_version arg
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return None
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try:
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from vllm.vllm_flash_attn.flash_attn_interface import (
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fa_version_unsupported_reason,
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is_fa_version_supported,
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)
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device_capability = current_platform.get_device_capability()
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assert device_capability is not None
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# 1. default version depending on platform
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fa_version = (
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3 if (device_capability.major == 9 and is_fa_version_supported(3)) else 2
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)
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# 2. override if passed by environment or config
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from vllm.config import get_current_vllm_config_or_none
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vllm_config = get_current_vllm_config_or_none()
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if (
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vllm_config is not None
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and vllm_config.attention_config.flash_attn_version is not None
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):
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fa_version = vllm_config.attention_config.flash_attn_version
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# 3. fallback for unsupported combinations
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if device_capability.major == 10 and fa_version == 3:
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logger.warning_once(
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"Cannot use FA version 3 on Blackwell platform, "
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"defaulting to FA version 2."
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)
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fa_version = 2
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if requires_alibi and fa_version == 3:
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logger.warning_once(
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"Cannot use FA version 3 with ALiBi, defaulting to FA version 2."
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)
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fa_version = 2
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if not is_fa_version_supported(fa_version):
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logger.error(
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"Cannot use FA version %d is not supported due to %s",
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fa_version,
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fa_version_unsupported_reason(fa_version),
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)
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assert is_fa_version_supported(fa_version)
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return fa_version
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except (ImportError, AssertionError):
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return None
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def flash_attn_supports_fp8() -> bool:
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return (
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get_flash_attn_version() == 3
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and current_platform.is_device_capability_family(90)
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)
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def flash_attn_supports_sinks() -> bool:
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if current_platform.is_xpu():
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return True
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else:
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return get_flash_attn_version() == 3
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def flash_attn_supports_mla():
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from vllm.platforms import current_platform
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if current_platform.is_cuda():
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try:
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from vllm.vllm_flash_attn.flash_attn_interface import (
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is_fa_version_supported,
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)
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return is_fa_version_supported(
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3
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) and current_platform.is_device_capability_family(90)
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except (ImportError, AssertionError):
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pass
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return False
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def is_flash_attn_varlen_func_available() -> bool:
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"""Check if flash_attn_varlen_func is available.
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This function determines whether the flash_attn_varlen_func imported at module
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level is a working implementation or a stub.
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Platform-specific sources:
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- CUDA: vllm.vllm_flash_attn.flash_attn_varlen_func
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- XPU: xpu_ops.flash_attn_varlen_func
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- ROCm: upstream flash_attn.flash_attn_varlen_func (if available)
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Note: This is separate from the AITER flash attention backend (rocm_aiter_fa.py)
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which uses rocm_aiter_ops.flash_attn_varlen_func. The condition to use AITER is
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handled separately via _aiter_ops.is_aiter_found_and_supported().
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Returns:
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bool: True if a working flash_attn_varlen_func implementation is available.
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"""
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if current_platform.is_cuda() or current_platform.is_xpu():
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# CUDA and XPU always have flash_attn_varlen_func available
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return True
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if current_platform.is_rocm():
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# Use the flag set during module import to check if
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# upstream flash-attn was successfully imported
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return _ROCM_FLASH_ATTN_AVAILABLE
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return False
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