Add --fast argument to enable experimental optimizations.

Optimizations that might break things/lower quality will be put behind
this flag first and might be enabled by default in the future.

Currently the only optimization is float8_e4m3fn matrix multiplication on
4000/ADA series Nvidia cards or later. If you have one of these cards you
will see a speed boost when using fp8_e4m3fn flux for example.

comfy/cli_args.py

@@ -123,6 +123,7 @@ parser.add_argument("--default-hashing-function", type=str, choices=['md5', 'sha
 
 parser.add_argument("--disable-smart-memory", action="store_true", help="Force ComfyUI to agressively offload to regular ram instead of keeping models in vram when it can.")
 parser.add_argument("--deterministic", action="store_true", help="Make pytorch use slower deterministic algorithms when it can. Note that this might not make images deterministic in all cases.")
+parser.add_argument("--fast", action="store_true", help="Enable some untested and potentially quality deteriorating optimizations.")
 
 parser.add_argument("--dont-print-server", action="store_true", help="Don't print server output.")
 parser.add_argument("--quick-test-for-ci", action="store_true", help="Quick test for CI.")

comfy/model_base.py

@@ -96,10 +96,7 @@ class BaseModel(torch.nn.Module):
 
         if not unet_config.get("disable_unet_model_creation", False):
             if model_config.custom_operations is None:
-                if self.manual_cast_dtype is not None:
-                    operations = comfy.ops.manual_cast
-                else:
-                    operations = comfy.ops.disable_weight_init
+                operations = comfy.ops.pick_operations(unet_config.get("dtype", None), self.manual_cast_dtype)
             else:
                 operations = model_config.custom_operations
             self.diffusion_model = unet_model(**unet_config, device=device, operations=operations)

comfy/model_management.py

@@ -1048,6 +1048,16 @@ def should_use_bf16(device=None, model_params=0, prioritize_performance=True, ma
 
     return False
 
+def supports_fp8_compute(device=None):
+    props = torch.cuda.get_device_properties(device)
+    if props.major >= 9:
+        return True
+    if props.major < 8:
+        return False
+    if props.minor < 9:
+        return False
+    return True
+
 def soft_empty_cache(force=False):
     global cpu_state
     if cpu_state == CPUState.MPS:

comfy/ops.py

@@ -18,7 +18,7 @@
 
 import torch
 import comfy.model_management
-
+from comfy.cli_args import args
 
 def cast_to(weight, dtype=None, device=None, non_blocking=False):
     if (dtype is None or weight.dtype == dtype) and (device is None or weight.device == device):
@@ -242,3 +242,42 @@ class manual_cast(disable_weight_init):
 
     class Embedding(disable_weight_init.Embedding):
         comfy_cast_weights = True
+
+
+def fp8_linear(self, input):
+    dtype = self.weight.dtype
+    if dtype not in [torch.float8_e4m3fn]:
+        return None
+
+    if len(input.shape) == 3:
+        out = torch.empty((input.shape[0], input.shape[1], self.weight.shape[0]), device=input.device, dtype=input.dtype)
+        inn = input.to(dtype)
+        non_blocking = comfy.model_management.device_supports_non_blocking(input.device)
+        w = cast_to(self.weight, device=input.device, non_blocking=non_blocking).t()
+        for i in range(input.shape[0]):
+            if self.bias is not None:
+                o, _ = torch._scaled_mm(inn[i], w, out_dtype=input.dtype, bias=cast_to_input(self.bias, input, non_blocking=non_blocking))
+            else:
+                o, _ = torch._scaled_mm(inn[i], w, out_dtype=input.dtype)
+            out[i] = o
+        return out
+    return None
+
+class fp8_ops(manual_cast):
+    class Linear(manual_cast.Linear):
+        def forward_comfy_cast_weights(self, input):
+            out = fp8_linear(self, input)
+            if out is not None:
+                return out
+
+            weight, bias = cast_bias_weight(self, input)
+            return torch.nn.functional.linear(input, weight, bias)
+
+
+def pick_operations(weight_dtype, compute_dtype, load_device=None):
+    if compute_dtype is None or weight_dtype == compute_dtype:
+        return disable_weight_init
+    if args.fast:
+        if comfy.model_management.supports_fp8_compute(load_device):
+            return fp8_ops
+    return manual_cast