118 lines
4.0 KiB
Python
118 lines
4.0 KiB
Python
import torch
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from einops import rearrange
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from flash_attn import flash_attn_func as flash_attn_func_v2
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from liger_kernel.ops.rope import LigerRopeFunction
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from torch import Tensor
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from typing import Tuple
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try:
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from flash_attn_interface import flash_attn_func as flash_attn_func_v3
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SUPPORT_FA3 = True
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except:
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SUPPORT_FA3 = False
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def flash_attn_func(q: Tensor, k: Tensor, v: Tensor) -> Tensor:
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if SUPPORT_FA3:
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return flash_attn_func_v3(q, k, v)[0]
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return flash_attn_func_v2(q, k, v)
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def attention(q: Tensor, k: Tensor, v: Tensor, pe) -> Tensor:
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if isinstance(pe, torch.Tensor):
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q, k = apply_rope(q, k, pe)
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else:
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cos, sin = pe
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q, k = LigerRopeFunction.apply(q, k, cos, sin)
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# to compare with the original implementation
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# k = reverse_rearrange_tensor(k)
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q = rearrange(q, "B H L D -> B L H D")
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k = rearrange(k, "B H L D -> B L H D")
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v = rearrange(v, "B H L D -> B L H D")
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x = flash_attn_func(q, k, v)
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x = rearrange(x, "B L H D -> B L (H D)")
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return x
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def liger_rope(pos: Tensor, dim: int, theta: int) -> Tuple:
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assert dim % 2 == 0
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scale = torch.arange(0, dim, 2, dtype=torch.float32, device=pos.device) / dim
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omega = 1.0 / (theta**scale)
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out = torch.einsum("...n,d->...nd", pos, omega) # (b, seq, dim//2)
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cos = out.cos()
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sin = out.sin()
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return (cos, sin)
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def rope(pos: Tensor, dim: int, theta: int) -> Tuple:
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assert dim % 2 == 0
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scale = torch.arange(0, dim, 2, dtype=torch.float64, device=pos.device) / dim
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omega = 1.0 / (theta**scale)
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out = torch.einsum("...n,d->...nd", pos, omega)
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out = torch.stack([torch.cos(out), -torch.sin(out), torch.sin(out), torch.cos(out)], dim=-1)
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out = rearrange(out, "b n d (i j) -> b n d i j", i=2, j=2)
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return out.float()
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def apply_rope(xq: Tensor, xk: Tensor, freqs_cis: Tensor) -> tuple[Tensor, Tensor]:
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xq_ = xq.float().reshape(*xq.shape[:-1], -1, 1, 2)
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xk_ = xk.float().reshape(*xk.shape[:-1], -1, 1, 2)
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xq_out = freqs_cis[..., 0] * xq_[..., 0] + freqs_cis[..., 1] * xq_[..., 1]
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xk_out = freqs_cis[..., 0] * xk_[..., 0] + freqs_cis[..., 1] * xk_[..., 1]
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return xq_out.reshape(*xq.shape).type_as(xq), xk_out.reshape(*xk.shape).type_as(xk)
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def rearrange_tensor(tensor):
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"""
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Rearranges the last dimension (D) of the input tensor based on the specified mapping:
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2d -> d, 2d+1 -> D/2 + d.
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Args:
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tensor (torch.Tensor): Input tensor of shape [B, H, L, D], where D is even.
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Returns:
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torch.Tensor: Tensor with rearranged last dimension, same shape as input.
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"""
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B, H, L, D = tensor.shape
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if D % 2 != 0:
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raise ValueError("The last dimension D must be even.")
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half_D = D // 2
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indices = torch.empty(D, dtype=torch.long, device=tensor.device)
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# Fill the indices based on the mapping rule
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indices[:half_D] = torch.arange(0, D, 2, device=tensor.device)
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indices[half_D:] = torch.arange(1, D, 2, device=tensor.device)
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# Rearrange the tensor based on the computed indices
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return tensor.index_select(dim=-1, index=indices)
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def reverse_rearrange_tensor(tensor):
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"""
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Restores the original order of the last dimension (D) of the input tensor based on the reverse mapping:
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d -> 2d, D/2 + d -> 2d + 1.
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Args:
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tensor (torch.Tensor): Input tensor of shape [B, H, L, D], where D is even.
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Returns:
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torch.Tensor: Tensor with restored original last dimension order, same shape as input.
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"""
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B, H, L, D = tensor.shape
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if D % 2 != 0:
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raise ValueError("The last dimension D must be even.")
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half_D = D // 2
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reverse_indices = torch.empty(D, dtype=torch.long, device=tensor.device)
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# Fill the reverse indices to restore the original order
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reverse_indices[::2] = torch.arange(half_D, device=tensor.device)
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reverse_indices[1::2] = torch.arange(half_D, D, device=tensor.device)
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# Rearrange the tensor based on the reverse indices
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return tensor.index_select(dim=-1, index=reverse_indices)
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