[GitHub] rahul003 commented on a change in pull request #10696: [MXNET-366]Extend MXNet Distributed Training by AllReduce

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rahul003 commented on a change in pull request #10696: [MXNET-366]Extend MXNet Distributed Training by AllReduce
URL: https://github.com/apache/incubator-mxnet/pull/10696#discussion_r195266548
 
 

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 File path: src/kvstore/collectives/include/coll_wrapper.h
 ##########
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * Copyright (c) 2018 by Contributors
+ */
+
+#ifndef MXNET_KVSTORE_COLLECTIVES_INCLUDE_COLL_WRAPPER_H_
+#define MXNET_KVSTORE_COLLECTIVES_INCLUDE_COLL_WRAPPER_H_
+
+#if MXNET_USE_ALLREDUCE_DIST_KVSTORE
+
+#include <mpi.h>
+
+#include "mxnet/ndarray.h"
+#include "mxnet/base.h"
+#include "mpi_message.pb.h"
+
+template<typename DType>
+MPI_Datatype MPI_Data_Type_Cast(void);
+
+template<>
+MPI_Datatype MPI_Data_Type_Cast<int>(void) {
+  return MPI_INT;
+}
+
+template<>
+MPI_Datatype MPI_Data_Type_Cast<float>(void) {
+  return MPI_FLOAT;
+}
+
+template<>
+MPI_Datatype MPI_Data_Type_Cast<double>(void) {
+  return MPI_DOUBLE;
+}
+
+template <class xpu, class DType>
+struct COLL_Wrapper {
+  static int Broadcast(mxnet::NDArray *input_array,
+                       int root_rank) {
+    return 0; }
+
+  static int AllReduce(mxnet::NDArray *input_array,
+                       mxnet::NDArray *output_array) {
+    return 0; }
+};
+
+// CPU Implementation
+template <class DType>
+struct COLL_Wrapper<mxnet::cpu, DType> {
+  static int Broadcast(mxnet::NDArray *input_array,
+                       int root_rank) {
+    DType *buf = reinterpret_cast<DType *>(input_array->data().dptr<DType>());
+    unsigned int count = input_array->data().Size();
+    int ret = MPI_Bcast(buf, count, MPI_Data_Type_Cast<DType>(), root_rank, MPI_COMM_WORLD);
+    return ret;
+  }
+
+  static int AllReduce(mxnet::NDArray *input_array,
+                       mxnet::NDArray *output_array) {
+    DType *send_buf = reinterpret_cast<DType *>(input_array->data().dptr<DType>());
+    DType *recv_buf = reinterpret_cast<DType *>(output_array->data().dptr<DType>());
+    unsigned int count = input_array->data().Size();
+    int ret;
+    assert(input_array->data().Size() == output_array->data().Size());
+
+    if (send_buf != recv_buf) {
+      ret = MPI_Allreduce(reinterpret_cast<const void *>(send_buf),
+                          reinterpret_cast<void *>(recv_buf),
+                          count, MPI_Data_Type_Cast<DType>(), MPI_SUM, MPI_COMM_WORLD);
+    } else {
 
 Review comment:
   Just for my understanding when can send_buf = recv_buf

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