add static scaling option

Author: drisspg

float8_experimental/float8_dynamic_linear.py

@@ -62,8 +62,10 @@ class Float8DynamicLinear(torch.nn.Linear):
     def __init__(self, **super_kwargs):
         super().__init__(**super_kwargs)
 
+        self.activation_scale: Optional[torch.Tensor] = None
+
     def forward(self, x):
-        x_fp8 = cast_to_float8_e4m3fn(x, self.forward_config)
+        x_fp8 = cast_to_float8_e4m3fn(x, self.forward_config, self.activation_scale)
         if isinstance(self.weight, Float8Tensor):  # cast by FSDP
             w_fp8 = self.weight
         else:
@@ -86,7 +88,11 @@ def static_quantize_weight(self, dtype: torch.dtype = torch.float8_e4m3fn) -> No
 
     @classmethod
     def from_float(
-        cls, mod, emulate: bool = False, static_quantize_weight: bool = False
+        cls,
+        mod,
+        emulate: bool = False,
+        static_quantize_weight: bool = False,
+        activation_scale: Optional[torch.Tensor] = None,
     ) -> "Float8DynamicLinear":
         """
         Create an nn.Linear with fp8 compute from a regular nn.Linear
@@ -96,6 +102,8 @@ def from_float(
             emulate (bool): whether to emulate fp8 matmul logic in float32
             static_quantize_weight (bool): whether to quantize the weight statically, this is useful
                 for inference where weights are not updated.
+            activation_scale (torch.Tensor): The scale of the input to this linear module, used for
+                for inference when a statically known scale is available.
         """
         with torch.device("meta"):
             super_kwargs = {
@@ -116,16 +124,38 @@ def from_float(
         if static_quantize_weight:
             new_mod.static_quantize_weight()
 
+        new_mod.activation_scale = activation_scale
         new_mod.bias = mod.bias
         return new_mod
 
 
 def cast_to_float8_e4m3fn(
-    inpt_tensor: torch.Tensor, mm_config: ScaledMMConfig, reduce_amax: bool = False
+    inpt_tensor: torch.Tensor,
+    mm_config: ScaledMMConfig,
+    reduce_amax: bool = False,
+    activation_scale: Optional[torch.Tensor] = None,
 ) -> Float8Tensor:
+    """Casts an input tensor to the Float8 (e4m3fn) format for efficient computation.
+
+    Args:
+        inpt_tensor: The input tensor to be cast.
+        mm_config: Configuration settings for the matrix multiplication
+        reduce_amax: Whether to reduce the amax (absolute maximum) among the local distributed group.
+        activation_scale: Optional tensor specifying the scale for activation. Default is None.
+
+    Returns:
+        Float8Tensor: The input tensor cast to Float8 (e4m3fn) format.
+
+    Note:
+        If the input tensor is already in Float8 format, it is returned as is without re-casting.
+    """
     if tensor_already_casted_to_fp8(inpt_tensor):
         return inpt_tensor
-    scale = tensor_to_scale(inpt_tensor, torch.float8_e4m3fn, reduce_amax)
+    scale = (
+        activation_scale
+        if activation_scale is not None
+        else tensor_to_scale(inpt_tensor, torch.float8_e4m3fn)
+    )
     return Float8Tensor.to_float8(
         inpt_tensor, scale, torch.float8_e4m3fn, mm_config=mm_config
     )