cherry-pick @Any-Winter-4079's invoke-ai/InvokeAI#540. this is a collaboration incorporating a lot of people's contributions -- including for example @Doggettx and the original code from @neonsecret on which the Doggetx optimizations were based (see invoke-ai/InvokeAI#431, https://github.com/sd-webui/stable-diffusion-webui/pull/771\#issuecomment-1239716055). Takes exactly the same amount of time to run 8 steps as original CompVis code does (10.4 secs, ~1.25s/it).

Author: Birch-san

ldm/modules/attention.py

@@ -1,4 +1,3 @@
-import gc
 from inspect import isfunction
 import math
 import torch
@@ -8,6 +7,8 @@
 
 from ldm.modules.diffusionmodules.util import checkpoint
 
+import psutil
+
 
 def exists(val):
     return val is not None
@@ -151,14 +152,13 @@ def forward(self, x):
 
 
 class CrossAttention(nn.Module):
-    def __init__(self, query_dim, context_dim=None, heads=8, dim_head=64, dropout=0., att_step=1):
+    def __init__(self, query_dim, context_dim=None, heads=8, dim_head=64, dropout=0.):
         super().__init__()
         inner_dim = dim_head * heads
         context_dim = default(context_dim, query_dim)
 
         self.scale = dim_head ** -0.5
         self.heads = heads
-        self.att_step = att_step
 
         self.to_q = nn.Linear(query_dim, inner_dim, bias=False)
         self.to_k = nn.Linear(context_dim, inner_dim, bias=False)
@@ -169,23 +169,50 @@ def __init__(self, query_dim, context_dim=None, heads=8, dim_head=64, dropout=0.
             nn.Dropout(dropout)
         )
 
-    def forward(self, x, context=None, mask=None):
-        h = self.heads
-
-        q_in = self.to_q(x)
-        context = default(context, x)
-
-        k_in = self.to_k(context)
-        v_in = self.to_v(context)
-
-        del context, x
-
-        q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> (b h) n d', h=h), (q_in, k_in, v_in))
-        del q_in, k_in, v_in
-
-
-        r1 = torch.zeros(q.shape[0], q.shape[1], v.shape[2], device=q.device)
-
+        if torch.cuda.is_available():
+            self.einsum_op = self.einsum_op_cuda
+        else:
+            self.mem_total = psutil.virtual_memory().total / (1024**3)
+            self.einsum_op = self.einsum_op_mps_v1 if self.mem_total >= 32 else self.einsum_op_mps_v2
+    
+    def einsum_op_compvis(self, q, k, v, r1):
+        s1 = einsum('b i d, b j d -> b i j', q, k) * self.scale # faster
+        s2 = s1.softmax(dim=-1, dtype=q.dtype)
+        del s1
+        r1 = einsum('b i j, b j d -> b i d', s2, v)
+        del s2
+        return r1
+
+    def einsum_op_mps_v1(self, q, k, v, r1):
+        if q.shape[1] <= 4096: # (512x512) max q.shape[1]: 4096
+            r1 = self.einsum_op_compvis(q, k, v, r1)
+        else:
+            slice_size = math.floor(2**30 / (q.shape[0] * q.shape[1]))
+            for i in range(0, q.shape[1], slice_size):
+                end = i + slice_size
+                s1 = einsum('b i d, b j d -> b i j', q[:, i:end], k) * self.scale
+                s2 = s1.softmax(dim=-1, dtype=r1.dtype)
+                del s1  
+                r1[:, i:end] = einsum('b i j, b j d -> b i d', s2, v)
+                del s2
+        return r1
+
+    def einsum_op_mps_v2(self, q, k, v, r1):
+        if self.mem_total >= 8 and q.shape[1] <= 4096:
+                r1 = self.einsum_op_compvis(q, k, v, r1)
+        else:
+            slice_size = 1
+            for i in range(0, q.shape[0], slice_size):
+                end = min(q.shape[0], i + slice_size)
+                s1 = einsum('b i d, b j d -> b i j', q[i:end], k[i:end])
+                s1 *= self.scale
+                s2 = s1.softmax(dim=-1, dtype=r1.dtype)
+                del s1
+                r1[i:end] = einsum('b i j, b j d -> b i d', s2, v[i:end])
+                del s2
+        return r1
+
+    def einsum_op_cuda(self, q, k, v, r1):
         stats = torch.cuda.memory_stats(q.device)
         mem_active = stats['active_bytes.all.current']
         mem_reserved = stats['reserved_bytes.all.current']
@@ -200,30 +227,39 @@ def forward(self, x, context=None, mask=None):
 
         if mem_required > mem_free_total:
             steps = 2**(math.ceil(math.log(mem_required / mem_free_total, 2)))
-            # print(f"Expected tensor size:{tensor_size/gb:0.1f}GB, cuda free:{mem_free_cuda/gb:0.1f}GB "
-            #       f"torch free:{mem_free_torch/gb:0.1f} total:{mem_free_total/gb:0.1f} steps:{steps}")
 
         if steps > 64:
             max_res = math.floor(math.sqrt(math.sqrt(mem_free_total / 2.5)) / 8) * 64
             raise RuntimeError(f'Not enough memory, use lower resolution (max approx. {max_res}x{max_res}). '
-                               f'Need: {mem_required/64/gb:0.1f}GB free, Have:{mem_free_total/gb:0.1f}GB free')
+                            f'Need: {mem_required/64/gb:0.1f}GB free, Have:{mem_free_total/gb:0.1f}GB free')
 
-        slice_size = q.shape[1] // steps if (q.shape[1] % steps) == 0 else q.shape[1]
+        slice_size = q.shape[1] // steps if (q.shape[1] % steps) == 0 else q.shape[1]  
         for i in range(0, q.shape[1], slice_size):
-            end = i + slice_size
+            end = min(q.shape[1], i + slice_size)
             s1 = einsum('b i d, b j d -> b i j', q[:, i:end], k) * self.scale
-
-            s2 = s1.softmax(dim=-1)
+            s2 = s1.softmax(dim=-1, dtype=r1.dtype)
             del s1
-
             r1[:, i:end] = einsum('b i j, b j d -> b i d', s2, v)
-            del s2
+            del s2 
+        return r1
 
-        del q, k, v
+    def forward(self, x, context=None, mask=None):
+        h = self.heads
 
+        q = self.to_q(x)
+        context = default(context, x)
+        del x
+        k = self.to_k(context)
+        v = self.to_v(context)
+        del context
+
+        q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> (b h) n d', h=h), (q, k, v))
+
+        r1 = torch.zeros(q.shape[0], q.shape[1], v.shape[2], device=q.device, dtype=q.dtype)
+        r1 = self.einsum_op(q, k, v, r1)
+        del q, k, v
         r2 = rearrange(r1, '(b h) n d -> b n (h d)', h=h)
         del r1
-
         return self.to_out(r2)
 
 
@@ -243,9 +279,10 @@ def forward(self, x, context=None):
         return checkpoint(self._forward, (x, context), self.parameters(), self.checkpoint)
 
     def _forward(self, x, context=None):
-        x = self.attn1(self.norm1(x)) + x
-        x = self.attn2(self.norm2(x), context=context) + x
-        x = self.ff(self.norm3(x)) + x
+        x = x.contiguous() if x.device.type == 'mps' else x
+        x += self.attn1(self.norm1(x))
+        x += self.attn2(self.norm2(x), context=context)
+        x += self.ff(self.norm3(x))
         return x
 
 
@@ -292,4 +329,4 @@ def forward(self, x, context=None):
             x = block(x, context=context)
         x = rearrange(x, 'b (h w) c -> b c h w', h=h, w=w)
         x = self.proj_out(x)
-        return x + x_in
+        return x + x_in