Add cross attention type for Sana-Sprint.

Author: scxue

src/diffusers/models/transformers/sana_transformer.py

@@ -14,6 +14,7 @@
 
 from typing import Any, Dict, Optional, Tuple, Union
 
+import math
 import torch
 import torch.nn.functional as F
 from torch import nn
@@ -184,6 +185,91 @@ def __call__(
 
         return hidden_states
 
+    
+class SanaAttnProcessor3_0:
+    r"""
+    Processor for implementing scaled dot-product attention (enabled by default if you're using PyTorch 2.0).
+    """
+
+    def __init__(self):
+        if not hasattr(F, "scaled_dot_product_attention"):
+            raise ImportError("SanaAttnProcessor2_0 requires PyTorch 2.0, to use it, please upgrade PyTorch to 2.0.")
+
+    @staticmethod
+    def scaled_dot_product_attention(query, key, value, attn_mask=None, dropout_p=0.0, is_causal=False, scale=None
+    ) -> torch.Tensor:
+        B, H, L, S = *query.size()[:-1], key.size(-2)
+        scale_factor = 1 / math.sqrt(query.size(-1)) if scale is None else scale
+        attn_bias = torch.zeros(B, H, L, S, dtype=query.dtype, device=query.device)
+
+        if attn_mask is not None:
+            if attn_mask.dtype == torch.bool:
+                attn_bias.masked_fill_(attn_mask.logical_not(), float("-inf"))
+            else:
+                attn_bias += attn_mask
+        attn_weight = query @ key.transpose(-2, -1) * scale_factor
+        attn_weight += attn_bias
+        attn_weight = torch.softmax(attn_weight, dim=-1)
+        attn_weight = torch.dropout(attn_weight, dropout_p, train=True)
+        return attn_weight @ value
+
+    #     return x
+    def __call__(
+        self,
+        attn: Attention,
+        hidden_states: torch.Tensor,
+        encoder_hidden_states: Optional[torch.Tensor] = None,
+        attention_mask: Optional[torch.Tensor] = None,
+    ) -> torch.Tensor:
+        batch_size, sequence_length, _ = (
+            hidden_states.shape if encoder_hidden_states is None else encoder_hidden_states.shape
+        )
+
+        if attention_mask is not None:
+            attention_mask = attn.prepare_attention_mask(attention_mask, sequence_length, batch_size)
+            # scaled_dot_product_attention expects attention_mask shape to be
+            # (batch, heads, source_length, target_length)
+            attention_mask = attention_mask.view(batch_size, attn.heads, -1, attention_mask.shape[-1])
+
+        query = attn.to_q(hidden_states)
+
+        if encoder_hidden_states is None:
+            encoder_hidden_states = hidden_states
+
+        key = attn.to_k(encoder_hidden_states)
+        value = attn.to_v(encoder_hidden_states)
+
+        if attn.norm_q is not None:
+            query = attn.norm_q(query)
+        if attn.norm_k is not None:
+            key = attn.norm_k(key)
+
+        inner_dim = key.shape[-1]
+        head_dim = inner_dim // attn.heads
+
+        query = query.view(batch_size, -1, attn.heads, head_dim).transpose(1, 2)
+
+        key = key.view(batch_size, -1, attn.heads, head_dim).transpose(1, 2)
+        value = value.view(batch_size, -1, attn.heads, head_dim).transpose(1, 2)
+
+        # the output of sdp = (batch, num_heads, seq_len, head_dim)
+        # TODO: add support for attn.scale when we move to Torch 2.1
+        hidden_states = self.scaled_dot_product_attention(
+            query, key, value, attn_mask=attention_mask, dropout_p=0.0, is_causal=False
+        )
+
+        hidden_states = hidden_states.transpose(1, 2).reshape(batch_size, -1, attn.heads * head_dim)
+        hidden_states = hidden_states.to(query.dtype)
+
+        # linear proj
+        hidden_states = attn.to_out[0](hidden_states)
+        # dropout
+        hidden_states = attn.to_out[1](hidden_states)
+
+        hidden_states = hidden_states / attn.rescale_output_factor
+
+        return hidden_states
+
 
 class SanaTransformerBlock(nn.Module):
     r"""
@@ -205,6 +291,7 @@ def __init__(
         attention_out_bias: bool = True,
         mlp_ratio: float = 2.5,
         qk_norm: Optional[str] = None,
+        cross_attention_type: str = "flash",
     ) -> None:
         super().__init__()
 
@@ -223,6 +310,12 @@ def __init__(
         )
 
         # 2. Cross Attention
+        if cross_attention_type == "flash":
+            cross_attention_processor = SanaAttnProcessor2_0()
+        elif cross_attention_type == "vanilla":
+            cross_attention_processor = SanaAttnProcessor3_0()
+        else:
+            raise ValueError(f"Cross attention type {cross_attention_type} is not defined.")
         if cross_attention_dim is not None:
             self.norm2 = nn.LayerNorm(dim, elementwise_affine=norm_elementwise_affine, eps=norm_eps)
             self.attn2 = Attention(
@@ -235,7 +328,7 @@ def __init__(
                 dropout=dropout,
                 bias=True,
                 out_bias=attention_out_bias,
-                processor=SanaAttnProcessor2_0(),
+                processor=cross_attention_processor,
             )
 
         # 3. Feed-forward
@@ -360,6 +453,7 @@ def __init__(
         guidance_embeds_scale: float = 0.1,
         qk_norm: Optional[str] = None,
         timestep_scale: float = 1.0,
+        cross_attention_type: str = "flash",
     ) -> None:
         super().__init__()
 
@@ -402,6 +496,7 @@ def __init__(
                     norm_eps=norm_eps,
                     mlp_ratio=mlp_ratio,
                     qk_norm=qk_norm,
+                    cross_attention_type=cross_attention_type,
                 )
                 for _ in range(num_layers)
             ]