Only test for xformers when enabling them #1773 (#1776)

* only check for xformers when xformers are enabled

* only test for xformers when enabling them

src/diffusers/models/attention.py

@@ -288,28 +288,29 @@ class AttentionBlock(nn.Module):
         self._use_memory_efficient_attention_xformers = False
 
     def set_use_memory_efficient_attention_xformers(self, use_memory_efficient_attention_xformers: bool):
-        if not is_xformers_available():
-            raise ModuleNotFoundError(
-                "Refer to https://github.com/facebookresearch/xformers for more information on how to install"
-                " xformers",
-                name="xformers",
-            )
-        elif not torch.cuda.is_available():
-            raise ValueError(
-                "torch.cuda.is_available() should be True but is False. xformers' memory efficient attention is only"
-                " available for GPU "
-            )
-        else:
-            try:
-                # Make sure we can run the memory efficient attention
-                _ = xformers.ops.memory_efficient_attention(
-                    torch.randn((1, 2, 40), device="cuda"),
-                    torch.randn((1, 2, 40), device="cuda"),
-                    torch.randn((1, 2, 40), device="cuda"),
+        if use_memory_efficient_attention_xformers:
+            if not is_xformers_available():
+                raise ModuleNotFoundError(
+                    "Refer to https://github.com/facebookresearch/xformers for more information on how to install"
+                    " xformers",
+                    name="xformers",
                 )
-            except Exception as e:
-                raise e
-            self._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
+            elif not torch.cuda.is_available():
+                raise ValueError(
+                    "torch.cuda.is_available() should be True but is False. xformers' memory efficient attention is only"
+                    " available for GPU "
+                )
+            else:
+                try:
+                    # Make sure we can run the memory efficient attention
+                    _ = xformers.ops.memory_efficient_attention(
+                        torch.randn((1, 2, 40), device="cuda"),
+                        torch.randn((1, 2, 40), device="cuda"),
+                        torch.randn((1, 2, 40), device="cuda"),
+                    )
+                except Exception as e:
+                    raise e
+        self._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
 
     def reshape_heads_to_batch_dim(self, tensor):
         batch_size, seq_len, dim = tensor.shape
@@ -450,31 +451,32 @@ class BasicTransformerBlock(nn.Module):
         self.norm3 = nn.LayerNorm(dim)
 
     def set_use_memory_efficient_attention_xformers(self, use_memory_efficient_attention_xformers: bool):
-        if not is_xformers_available():
-            print("Here is how to install it")
-            raise ModuleNotFoundError(
-                "Refer to https://github.com/facebookresearch/xformers for more information on how to install"
-                " xformers",
-                name="xformers",
-            )
-        elif not torch.cuda.is_available():
-            raise ValueError(
-                "torch.cuda.is_available() should be True but is False. xformers' memory efficient attention is only"
-                " available for GPU "
-            )
-        else:
-            try:
-                # Make sure we can run the memory efficient attention
-                _ = xformers.ops.memory_efficient_attention(
-                    torch.randn((1, 2, 40), device="cuda"),
-                    torch.randn((1, 2, 40), device="cuda"),
-                    torch.randn((1, 2, 40), device="cuda"),
+        if use_memory_efficient_attention_xformers:
+            if not is_xformers_available():
+                print("Here is how to install it")
+                raise ModuleNotFoundError(
+                    "Refer to https://github.com/facebookresearch/xformers for more information on how to install"
+                    " xformers",
+                    name="xformers",
                 )
-            except Exception as e:
-                raise e
-            self.attn1._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
-            if self.attn2 is not None:
-                self.attn2._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
+            elif not torch.cuda.is_available():
+                raise ValueError(
+                    "torch.cuda.is_available() should be True but is False. xformers' memory efficient attention is only"
+                    " available for GPU "
+                )
+            else:
+                try:
+                    # Make sure we can run the memory efficient attention
+                    _ = xformers.ops.memory_efficient_attention(
+                        torch.randn((1, 2, 40), device="cuda"),
+                        torch.randn((1, 2, 40), device="cuda"),
+                        torch.randn((1, 2, 40), device="cuda"),
+                    )
+                except Exception as e:
+                    raise e
+        self.attn1._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
+        if self.attn2 is not None:
+            self.attn2._use_memory_efficient_attention_xformers = use_memory_efficient_attention_xformers
 
     def forward(self, hidden_states, encoder_hidden_states=None, timestep=None, attention_mask=None):
         # 1. Self-Attention