mx roofline: adjust mxfp8 formulas (#1953)

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Author: vkuzo

torchao/testing/float8/roofline_utils.py

@@ -183,27 +183,16 @@ def get_tensor_memory_traffic_ovhd_s(
             "mxfp8_cutlass",
             "mxfp8_cublas",
         ), "unsupported"
-
-        if tensor_role == "weight":
-            # x_bf16 = ...
-            # kernel 1:               x_bf16 -> x_mxfp8_dim0
-            # kernel 2:               x_bf16 -> x_mxfp8_dim1
-            if fuse_with_prev:
-                kernel_1_rw = 0 + BYTES_PER_EL_FLOAT8 * numel
-            else:
-                kernel_1_rw = BYTES_PER_EL_BF16 * numel + BYTES_PER_EL_FLOAT8 * numel
-            kernel_2_rw = BYTES_PER_EL_BF16 * numel + BYTES_PER_EL_FLOAT8 * numel
-            res_bytes = [kernel_1_rw, kernel_2_rw]
+        # For now, assume that we can't profitably fuse kernel 1 and kernel 2
+        # x_bf16 = ...
+        # kernel 1:               x_bf16 -> x_mxfp8_dim0
+        # kernel 2:               x_bf16 -> x_mxfp8_dim1
+        if fuse_with_prev:
+            kernel_1_rw = 0 + BYTES_PER_EL_FLOAT8 * numel
         else:
-            # x_bf16 = ...
-            # kernel 1:               x_bf16 -> x_mxfp8_dim0, x_mxfp8_dim1
-            if fuse_with_prev:
-                kernel_1_rw = 0 + BYTES_PER_EL_FLOAT8 * numel * 2
-            else:
-                kernel_1_rw = (
-                    BYTES_PER_EL_BF16 * numel + BYTES_PER_EL_FLOAT8 * numel * 2
-                )
-            res_bytes = [kernel_1_rw]
+            kernel_1_rw = BYTES_PER_EL_BF16 * numel + BYTES_PER_EL_FLOAT8 * numel
+        kernel_2_rw = BYTES_PER_EL_BF16 * numel + BYTES_PER_EL_FLOAT8 * numel
+        res_bytes = [kernel_1_rw, kernel_2_rw]
 
     # convert from bytes to seconds
     res_s = [