clarify MKLDNN INT8 Mul Op attributes (#18685)

paddle/fluid/operators/mkldnn/mul_mkldnn_op.cc

@@ -207,6 +207,14 @@ class QuantMulPrimitiveFactory : public MulPrimitiveFactory<XT, YT, OT> {
     int y_num_col_dims = ctx.Attr<int>("y_num_col_dims");
     auto scale_y = ctx.Attr<std::vector<float>>("scale_y");
 
+    // TODO(intel-minghui) : Remove the restriction that only supports Input(Y)
+    // as weights
+    bool enforce = std::is_same<YT, float>::value;
+    PADDLE_ENFORCE(
+        enforce == true,
+        "Input(Y) supposed to be fp32 data type since only fp32 data type is "
+        "supported in the current design of MKLDNN INT8.");
+
     auto x_matrix =
         this->template UpdateDataFormat<XT>(x_input, x_num_col_dims, ctx);
     auto y_matrix =

paddle/fluid/operators/mul_op.cc

@@ -144,13 +144,17 @@ class MulOpMaker : public framework::OpProtoAndCheckerMaker {
         )DOC")
         .SetDefault(1)
         .EqualGreaterThan(1);
-    AddAttr<float>("scale_x",
-                   "scale_x to used for int8 input data x."
-                   "Only used with MKL-DNN INT8")
+    AddAttr<float>(
+        "scale_x",
+        "scale_x to be used for int8 mul input data x. scale_x has the"
+        "same purpose as scale_in in OPs that support quantization."
+        "Only to be used with MKL-DNN INT8")
         .SetDefault(1.0f);
-    AddAttr<std::vector<float>>("scale_y",
-                                "scale_y to used for int8 input data y."
-                                "Only used with MKL-DNN INT8")
+    AddAttr<std::vector<float>>(
+        "scale_y",
+        "scale_y to be used for int8 mul input data y. scale_y has the"
+        "same purpose as scale_weights in OPs that support quantization."
+        "Only to be used with MKL-DNN INT8")
         .SetDefault({1.0f});
     AddAttr<float>("scale_out",
                    "scale_out to be used for int8 output data."