skip reset mkldnn when input size does not change

paddle/gserver/layers/MkldnnLayer.cpp

@@ -49,7 +49,6 @@ void MkldnnLayer::resetForwardFC(int bs,
                                  real* wgtData,
                                  real* biasData) {
   bool hasSpatial = ih == 1 && iw == 1 ? false : true;
-
   mem::desc botMD = hasSpatial ? createMD({bs, ic, ih, iw}, format::nchw)
                                : createMD({bs, ic}, format::nc);
   mem::desc wgtMD = hasSpatial ? createMD({oc, ic, ih, iw}, format::oihw)
@@ -58,7 +57,12 @@ void MkldnnLayer::resetForwardFC(int bs,
                                       : createMD({}, format::format_undef);
   mem::desc topMD = createMD({bs, oc}, format::nc);
 
-  inVal_.reset(new mem(mem::primitive_desc(botMD, engine_), botData));
+  mem::primitive_desc botPD = mem::primitive_desc(botMD, engine_);
+  if (inVal_ && inVal_->get_primitive_desc() == botPD) {
+    return;
+  }
+
+  inVal_.reset(new mem(botPD, botData));
   wgtVal_.reset(new mem(mem::primitive_desc(wgtMD, engine_), wgtData));
   outVal_.reset(new mem(mem::primitive_desc(topMD, engine_), topData));
 
@@ -111,7 +115,6 @@ void MkldnnLayer::resetBackwardFC(int bs,
                                   real* wgtData,
                                   real* biasDiff) {
   bool hasSpatial = ih == 1 && iw == 1 ? false : true;
-  engine_ = CpuEngine::Instance().getEngine();
 
   // backward weight
   mem::desc botMD = hasSpatial ? createMD({bs, ic, ih, iw}, format::nchw)
@@ -122,9 +125,19 @@ void MkldnnLayer::resetBackwardFC(int bs,
   mem::desc biasMD = biasDiff != NULL ? createMD({oc}, format::x)
                                       : createMD({}, format::format_undef);
 
-  inVal_.reset(new mem(mem::primitive_desc(botMD, engine_), botData));
+  mem::primitive_desc topPD = mem::primitive_desc(botMD, engine_);
+  if (outGrad_ && outGrad_->get_primitive_desc() == topPD) {
+    return;
+  }
+
+  if (inVal_) {
+    // update data
+    inVal_->set_data_handle(botData);
+  } else {
+    inVal_.reset(new mem(mem::primitive_desc(botMD, engine_), botData));
+  }
   wgtGrad_.reset(new mem(mem::primitive_desc(wgtMD, engine_), wgtDiff));
-  outGrad_.reset(new mem(mem::primitive_desc(topMD, engine_), topDiff));
+  outGrad_.reset(new mem(topPD, topDiff));
 
   fc_fwd::desc fwdDesc =
       fc_fwd::desc(mkldnn::prop_kind::forward, botMD, wgtMD, topMD);
@@ -154,7 +167,12 @@ void MkldnnLayer::resetBackwardFC(int bs,
   fc_bwdData::primitive_desc bwdDataPD =
       fc_bwdData::primitive_desc(bwdDataDesc, engine_, fwdPD);
   inGrad_.reset(new mem(mem::primitive_desc(botMD, engine_), botDiff));
-  wgtVal_.reset(new mem(mem::primitive_desc(wgtMD, engine_), wgtData));
+  if (wgtVal_) {
+    // update data
+    wgtVal_->set_data_handle(wgtData);
+  } else {
+    wgtVal_.reset(new mem(mem::primitive_desc(wgtMD, engine_), wgtData));
+  }
   bwdData_.reset(new fc_bwdData(bwdDataPD, *outGrad_, *wgtVal_, *inGrad_));
   pipelineBwd_.push_back(*bwdData_);
 }