[GitHub] [incubator-mxnet] TaoLv commented on a change in pull request #17170: add mkldnn softmax backward

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TaoLv commented on a change in pull request #17170: add mkldnn softmax backward 
URL: https://github.com/apache/incubator-mxnet/pull/17170#discussion_r366408821
 
 

 ##########
 File path: src/operator/nn/mkldnn/mkldnn_softmax.cc
 ##########
 @@ -131,6 +143,80 @@ void MKLDNNSoftmaxForward(const nnvm::NodeAttrs& attrs,
   stream->Submit();
 }
 
+class MKLDNNSoftmaxBwd {
+ public:
+  mkldnn::softmax_backward::primitive_desc pd;
+
+  MKLDNNSoftmaxBwd(const mkldnn::memory &diff_mem,
+                   const mkldnn::memory &data_mem,
+                   const int axis,
+                   const mkldnn::softmax_forward::primitive_desc &hint_fwd_pd) 
:
+                                 pd(GetSoftmaxBwdPd(diff_mem, data_mem, axis, 
hint_fwd_pd)) {
+    bwd_ = std::make_shared<mkldnn::softmax_backward>(pd);
+  }
+
+  const mkldnn::softmax_backward &GetBwd() const {
+    return *bwd_;
+  }
+
+ private:
+  std::shared_ptr<mkldnn::softmax_backward> bwd_;
+};
+
+typedef ParamOpSign<SoftmaxParam> MKLDNNSoftmaxSignature;
+
+static MKLDNNSoftmaxBwd &GetSoftmaxBwd(const SoftmaxParam &param,
+                                       const int real_axis,
+                                       const std::vector<NDArray> &data,
+                                       const std::vector<NDArray> &output) {
+#if DMLC_CXX11_THREAD_LOCAL
+  static thread_local std::unordered_map<MKLDNNSoftmaxSignature, 
MKLDNNSoftmaxBwd, OpHash> bwds;
+#else
+  static MX_THREAD_LOCAL std::unordered_map<MKLDNNSoftmaxSignature, 
MKLDNNSoftmaxBwd, OpHash> bwds;
+#endif
+
+  MKLDNNSoftmaxSignature key(param);
+  key.AddSign(real_axis);
+  key.AddSign(data);
+  key.AddSign(output);
+
+  auto it = bwds.find(key);
+  if (it == bwds.end()) {
+    auto diff_mem = data[0].GetMKLDNNData();
+    auto data_mem = data[1].GetMKLDNNData();
+    auto fwd_pd = GetSoftmaxFwdPd(true, real_axis, *data_mem);
+    MKLDNNSoftmaxBwd bwd(*diff_mem, *data_mem, real_axis, fwd_pd);
+    it = AddToCache(&bwds, key, bwd);
+  }
+  return it->second;
+}
+
+void MKLDNNSoftmaxBackward(const nnvm::NodeAttrs& attrs,
+                           const OpContext &ctx,
+                           const std::vector<NDArray> &in_data,
+                           const std::vector<OpReqType>& req,
+                           const std::vector<NDArray> &out_data) {
+  if (req[0] == kNullOp) return;
+  CHECK_EQ(in_data.size(), 2U);
+  const SoftmaxParam& param = nnvm::get<SoftmaxParam>(attrs.parsed);
+  int axis = CheckAxis(param.axis, in_data[1].shape().ndim());
+  auto diff_mem = in_data[0].GetMKLDNNData();
+  auto data_mem = in_data[1].GetMKLDNNData();
+  auto bwd = GetSoftmaxBwd(param, axis, in_data, out_data);
+
+  auto out_mem = CreateMKLDNNMem(out_data[0], bwd.pd.diff_src_desc(), req[0]);
 
 Review comment:
   1. Please check if you want to support req=kAddTo;
   2. softmax backward primitive should support in-place calculation so no need 
to create additional buffer.

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