From f859fdf7ba742e66c1e4f809cfebda59cd94aa64 Mon Sep 17 00:00:00 2001
From: Aryan <aryan@huggingface.co>
Date: Wed, 16 Jul 2025 21:31:53 +0200
Subject: [PATCH] refactor; support flash attention 2 with cp

---
 src/diffusers/models/attention_dispatch.py | 53 ++++++++++++++--------
 1 file changed, 33 insertions(+), 20 deletions(-)

diff --git a/src/diffusers/models/attention_dispatch.py b/src/diffusers/models/attention_dispatch.py
index 07a9c09b5e..6357bdad0f 100644
--- a/src/diffusers/models/attention_dispatch.py
+++ b/src/diffusers/models/attention_dispatch.py
@@ -571,8 +571,8 @@ class _cudnn_attention(torch.autograd.Function):
         value: torch.Tensor,
         attn_mask: Optional[torch.Tensor] = None,
         dropout_p: float = 0.0,
-        scale: Optional[float] = None,
         is_causal: bool = False,
+        scale: Optional[float] = None,
         enable_gqa: bool = False,
         return_lse: bool = False,
     ):
@@ -653,8 +653,8 @@ class _flash_attention_2(torch.autograd.Function):
         value: torch.Tensor,
         attn_mask: Optional[torch.Tensor] = None,
         dropout_p: float = 0.0,
-        scale: Optional[float] = None,
         is_causal: bool = False,
+        scale: Optional[float] = None,
         enable_gqa: bool = False,
         return_lse: bool = False,
     ):
@@ -753,8 +753,8 @@ class TemplatedRingAttention(torch.autograd.Function):
         value: torch.Tensor,
         attn_mask: Optional[torch.Tensor],
         dropout_p: float,
-        scale: Optional[float],
         is_causal: bool,
+        scale: Optional[float],
         enable_gqa: bool,
         return_lse: bool,
         op: torch.autograd.Function,
@@ -778,7 +778,7 @@ class TemplatedRingAttention(torch.autograd.Function):
                 value = kv[key.numel() :].reshape_as(value)
                 next_rank = (next_rank + 1) % world_size
 
-            out, lse = op.apply(query, key, value, attn_mask, dropout_p, scale, is_causal, enable_gqa, True)
+            out, lse = op.apply(query, key, value, attn_mask, dropout_p, is_causal, scale, enable_gqa, True)
 
             if parallel_config.convert_to_fp32:
                 out = out.to(torch.float32)
@@ -813,8 +813,8 @@ class TemplatedUlyssesAttention(torch.autograd.Function):
         value: torch.Tensor,
         attn_mask: Optional[torch.Tensor],
         dropout_p: float,
-        scale: Optional[float],
         is_causal: bool,
+        scale: Optional[float],
         enable_gqa: bool,
         return_lse: bool,
         op: torch.autograd.Function,
@@ -833,7 +833,7 @@ class TemplatedUlyssesAttention(torch.autograd.Function):
         query, key, value = (funcol.all_to_all_single(x, None, None, group=group).wait() for x in (query, key, value))
         query, key, value = (x.flatten(0, 1).permute(1, 0, 2, 3).contiguous() for x in (query, key, value))
 
-        out = op.apply(query, key, value, attn_mask, dropout_p, scale, is_causal, enable_gqa, return_lse)
+        out = op.apply(query, key, value, attn_mask, dropout_p, is_causal, scale, enable_gqa, return_lse)
         if return_lse:
             out, lse, *_ = out
 
@@ -883,14 +883,14 @@ def _templated_context_parallel_attention(
     # TODO: add support for unified attention with ring/ulysses degree both being > 1
     if parallel_config.ring_degree > 1:
         return TemplatedRingAttention.apply(
-            query, key, value, attn_mask, dropout_p, scale, is_causal, enable_gqa, return_lse, op
+            query, key, value, attn_mask, dropout_p, is_causal, scale, enable_gqa, return_lse, op
         )
     elif parallel_config.ulysses_degree > 1:
         return TemplatedUlyssesAttention.apply(
-            query, key, value, attn_mask, dropout_p, scale, is_causal, enable_gqa, return_lse, op
+            query, key, value, attn_mask, dropout_p, is_causal, scale, enable_gqa, return_lse, op
         )
     else:
-        return op.apply(query, key, value, attn_mask, dropout_p, scale, is_causal, enable_gqa, return_lse)
+        return op.apply(query, key, value, attn_mask, dropout_p, is_causal, scale, enable_gqa, return_lse)
 
 
 # ===== Attention backends =====
@@ -905,20 +905,33 @@ def _flash_attention(
     key: torch.Tensor,
     value: torch.Tensor,
     dropout_p: float = 0.0,
-    scale: Optional[float] = None,
     is_causal: bool = False,
+    scale: Optional[float] = None,
     return_lse: bool = False,
 ) -> torch.Tensor:
-    out = flash_attn_func(
-        q=query,
-        k=key,
-        v=value,
-        dropout_p=dropout_p,
-        softmax_scale=scale,
-        causal=is_causal,
-        return_attn_probs=return_lse,
-    )
-    return out
+    parallel_config = _AttentionBackendRegistry._parallel_config
+
+    lse = None
+    if parallel_config is None:
+        out = flash_attn_func(
+            q=query,
+            k=key,
+            v=value,
+            dropout_p=dropout_p,
+            softmax_scale=scale,
+            causal=is_causal,
+            return_attn_probs=return_lse,
+        )
+        if return_lse:
+            out, lse, *_ = out
+    else:
+        out = _templated_context_parallel_attention(
+            query, key, value, None, dropout_p, is_causal, scale, False, return_lse, op=_flash_attention_2
+        )
+        if return_lse:
+            out, lse = out
+
+    return (out, lse) if return_lse else out
 
 
 @_AttentionBackendRegistry.register(