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97 lines
3.7 KiB
97 lines
3.7 KiB
from ..base_extension import _Extension
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class FlashAttentionDaoCudaExtension(_Extension):
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def __init__(self):
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super().__init__(name="flash_attention_dao_cuda", support_aot=False, support_jit=False, priority=10)
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def is_available(self) -> bool:
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# cuda extension can only be built if cuda is available
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try:
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import torch
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from flash_attn import flash_attn_func, flash_attn_varlen_kvpacked_func # noqa
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from flash_attn.bert_padding import index_first_axis, pad_input # noqa
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cuda_available = torch.cuda.is_available()
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except:
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cuda_available = False
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return cuda_available
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def assert_compatible(self) -> bool:
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pass
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def build_aot(self) -> None:
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raise NotImplementedError(
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"We rely on the third-party flash-attn library for flash attention (https://github.com/Dao-AILab/flash-attention). Please install flash-attn via 'pip install flash-attn --no-build-isolation'."
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)
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def build_jit(self) -> None:
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raise NotImplementedError(
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"We rely on the third-party flash-attn library for flash attention (https://github.com/Dao-AILab/flash-attention). Please install flash-attn via 'pip install flash-attn --no-build-isolation'"
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)
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def load(self):
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from typing import Optional
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import torch
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from einops import rearrange
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from flash_attn import flash_attn_func, flash_attn_varlen_kvpacked_func
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from flash_attn.bert_padding import index_first_axis, pad_input
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def _unpad_input(hidden_states: torch.Tensor, indices: torch.Tensor):
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return index_first_axis(rearrange(hidden_states, "b s ... -> (b s) ..."), indices)
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def flash_attention(
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q: torch.Tensor,
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k: torch.Tensor,
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v: torch.Tensor,
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dropout_p: float = 0.0,
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scale: Optional[float] = None,
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attention_mask: Optional[torch.Tensor] = None,
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is_causal: bool = False,
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cu_seqlens_q: Optional[torch.Tensor] = None,
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cu_seqlens_kv: Optional[torch.Tensor] = None,
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max_seqlen_q: Optional[int] = None,
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max_seqlen_kv: Optional[int] = None,
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q_indices: Optional[torch.Tensor] = None,
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kv_indices: Optional[torch.Tensor] = None,
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):
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# [B, N, S, D] -> [B, S, N, D]
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q = q.transpose(1, 2)
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k = k.transpose(1, 2)
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v = v.transpose(1, 2)
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b, s_q = q.shape[:2]
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if cu_seqlens_q is not None:
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# padded / padded causal
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# unpad input: [B, S, N, D] -> [T, N, D]
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q = _unpad_input(q, q_indices)
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kv = _unpad_input(torch.stack(tensors=(k, v), dim=2), kv_indices)
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attn_output = flash_attn_varlen_kvpacked_func(
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q,
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kv,
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cu_seqlens_q,
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cu_seqlens_kv,
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max_seqlen_q,
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max_seqlen_kv,
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dropout_p=dropout_p,
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softmax_scale=scale,
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causal=is_causal,
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)
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# pad output: [T, N, D] -> [B, S, N, D]
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attn_output = pad_input(attn_output, q_indices, b, s_q)
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else:
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# causal / no attn mask
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attn_output = flash_attn_func(
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q,
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k,
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v,
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dropout_p=dropout_p,
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softmax_scale=scale,
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causal=is_causal,
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)
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# [B, S, N, D] -> [B, N, S, D]
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return attn_output.transpose(1, 2)
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return flash_attention
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