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import importlib.metadata
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import math
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import torch
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import torch.nn as nn
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import torch.nn.functional as F
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try:
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import flash_attn
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from flash_attn.flash_attn_interface import _flash_attn_forward
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from flash_attn.flash_attn_interface import flash_attn_varlen_func
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except ImportError:
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flash_attn = None
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flash_attn_varlen_func = None
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_flash_attn_forward = None
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MEMORY_LAYOUT = {
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"flash": (
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lambda x: x.view(x.shape[0] * x.shape[1], *x.shape[2:]),
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lambda x: x,
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),
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"torch": (
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lambda x: x.transpose(1, 2),
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lambda x: x.transpose(1, 2),
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),
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"vanilla": (
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lambda x: x.transpose(1, 2),
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lambda x: x.transpose(1, 2),
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),
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}
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def get_cu_seqlens(text_mask, img_len):
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"""Calculate cu_seqlens_q, cu_seqlens_kv using text_mask and img_len
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Args:
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text_mask (torch.Tensor): the mask of text
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img_len (int): the length of image
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Returns:
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torch.Tensor: the calculated cu_seqlens for flash attention
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"""
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batch_size = text_mask.shape[0]
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text_len = text_mask.sum(dim=1)
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max_len = text_mask.shape[1] + img_len
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cu_seqlens = torch.zeros([2 * batch_size + 1], dtype=torch.int32, device="cuda")
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for i in range(batch_size):
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s = text_len[i] + img_len
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s1 = i * max_len + s
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s2 = (i + 1) * max_len
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cu_seqlens[2 * i + 1] = s1
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cu_seqlens[2 * i + 2] = s2
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return cu_seqlens
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def attention(
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q,
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k,
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v,
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mode="flash",
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drop_rate=0,
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attn_mask=None,
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causal=False,
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cu_seqlens_q=None,
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cu_seqlens_kv=None,
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max_seqlen_q=None,
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max_seqlen_kv=None,
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batch_size=1,
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):
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"""
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Perform QKV self attention.
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Args:
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q (torch.Tensor): Query tensor with shape [b, s, a, d], where a is the number of heads.
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k (torch.Tensor): Key tensor with shape [b, s1, a, d]
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v (torch.Tensor): Value tensor with shape [b, s1, a, d]
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mode (str): Attention mode. Choose from 'self_flash', 'cross_flash', 'torch', and 'vanilla'.
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drop_rate (float): Dropout rate in attention map. (default: 0)
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attn_mask (torch.Tensor): Attention mask with shape [b, s1] (cross_attn), or [b, a, s, s1] (torch or vanilla).
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(default: None)
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causal (bool): Whether to use causal attention. (default: False)
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cu_seqlens_q (torch.Tensor): dtype torch.int32. The cumulative sequence lengths of the sequences in the batch,
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used to index into q.
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cu_seqlens_kv (torch.Tensor): dtype torch.int32. The cumulative sequence lengths of the sequences in the batch,
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used to index into kv.
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max_seqlen_q (int): The maximum sequence length in the batch of q.
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max_seqlen_kv (int): The maximum sequence length in the batch of k and v.
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Returns:
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torch.Tensor: Output tensor after self attention with shape [b, s, ad]
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"""
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pre_attn_layout, post_attn_layout = MEMORY_LAYOUT[mode]
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q = pre_attn_layout(q)
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k = pre_attn_layout(k)
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v = pre_attn_layout(v)
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if mode == "torch":
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if attn_mask is not None and attn_mask.dtype != torch.bool:
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attn_mask = attn_mask.to(q.dtype)
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x = F.scaled_dot_product_attention(
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q, k, v, attn_mask=attn_mask, dropout_p=drop_rate, is_causal=causal
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)
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elif mode == "flash":
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x = flash_attn_varlen_func(
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q,
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k,
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v,
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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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)
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x = x.view(
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batch_size, max_seqlen_q, x.shape[-2], x.shape[-1]
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)
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elif mode == "vanilla":
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scale_factor = 1 / math.sqrt(q.size(-1))
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b, a, s, _ = q.shape
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s1 = k.size(2)
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attn_bias = torch.zeros(b, a, s, s1, dtype=q.dtype, device=q.device)
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if causal:
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assert (
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attn_mask is None
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), "Causal mask and attn_mask cannot be used together"
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temp_mask = torch.ones(b, a, s, s, dtype=torch.bool, device=q.device).tril(
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diagonal=0
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)
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attn_bias.masked_fill_(temp_mask.logical_not(), float("-inf"))
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attn_bias.to(q.dtype)
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if attn_mask is not None:
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if attn_mask.dtype == torch.bool:
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attn_bias.masked_fill_(attn_mask.logical_not(), float("-inf"))
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else:
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attn_bias += attn_mask
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attn = (q @ k.transpose(-2, -1)) * scale_factor
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attn += attn_bias
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attn = attn.softmax(dim=-1)
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attn = torch.dropout(attn, p=drop_rate, train=True)
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x = attn @ v
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else:
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raise NotImplementedError(f"Unsupported attention mode: {mode}")
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x = post_attn_layout(x)
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b, s, a, d = x.shape
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out = x.reshape(b, s, -1)
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return out
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def parallel_attention(
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hybrid_seq_parallel_attn,
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q,
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k,
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v,
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img_q_len,
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img_kv_len,
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cu_seqlens_q,
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cu_seqlens_kv
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):
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attn1 = hybrid_seq_parallel_attn(
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None,
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q[:, :img_q_len, :, :],
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k[:, :img_kv_len, :, :],
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v[:, :img_kv_len, :, :],
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dropout_p=0.0,
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causal=False,
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joint_tensor_query=q[:,img_q_len:cu_seqlens_q[1]],
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joint_tensor_key=k[:,img_kv_len:cu_seqlens_kv[1]],
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joint_tensor_value=v[:,img_kv_len:cu_seqlens_kv[1]],
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joint_strategy="rear",
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)
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if flash_attn.__version__ >= '2.7.0':
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attn2, *_ = _flash_attn_forward(
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q[:,cu_seqlens_q[1]:],
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k[:,cu_seqlens_kv[1]:],
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v[:,cu_seqlens_kv[1]:],
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dropout_p=0.0,
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softmax_scale=q.shape[-1] ** (-0.5),
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causal=False,
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window_size_left=-1,
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window_size_right=-1,
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softcap=0.0,
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alibi_slopes=None,
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return_softmax=False,
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)
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else:
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attn2, *_ = _flash_attn_forward(
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q[:,cu_seqlens_q[1]:],
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k[:,cu_seqlens_kv[1]:],
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v[:,cu_seqlens_kv[1]:],
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dropout_p=0.0,
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softmax_scale=q.shape[-1] ** (-0.5),
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causal=False,
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window_size=(-1, -1),
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softcap=0.0,
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alibi_slopes=None,
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return_softmax=False,
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)
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attn = torch.cat([attn1, attn2], dim=1)
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b, s, a, d = attn.shape
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attn = attn.reshape(b, s, -1)
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return attn
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