Add gperftools into imperative tracer

test=develop

paddle/fluid/imperative/tracer.cc

@@ -20,9 +20,23 @@
 #include "paddle/fluid/platform/device_context.h"
 #include "paddle/fluid/platform/enforce.h"
 
+#ifdef WITH_GPERFTOOLS
+#include "gperftools/profiler.h"
+#endif
+
+DEFINE_string(
+    tracer_profile_fname, "",
+    "Profiler filename for imperative tracer, which generated by gperftools."
+    "Only valid when compiled `WITH_PROFILER=ON`. Empty if disable.");
+
 namespace paddle {
 namespace imperative {
 
+static std::once_flag gTracerProfileOnce;
+#ifdef WITH_GPERFTOOLS
+static bool gTracerProfilerStarted = false;
+#endif
+
 void CreateGradOp(const framework::OpDesc& op_desc,
                   const std::unordered_set<std::string>& no_grad_set,
                   const std::vector<framework::BlockDesc*>& grad_sub_block,
@@ -68,11 +82,31 @@ platform::Place GetExpectedPlace(platform::Place place, VarBasePtrMap inputs) {
   return result;
 }
 
+Tracer::Tracer(framework::BlockDesc* root_block) : root_block_(root_block) {
+  if (!FLAGS_tracer_profile_fname.empty()) {
+    std::call_once(gTracerProfileOnce, [] {
+#ifdef WITH_GPERFTOOLS
+      ProfilerStart(FLAGS_tracer_profile_fname.c_str());
+      gTracerProfilerStarted = true;
+#else
+      LOG(WARNING) << "Paddle is not compiled with gperftools. "
+                      "FLAGS_tracer_profile_fname will be ignored";
+#endif
+    });
+  }
+}
+
 std::set<std::string> Tracer::Trace(OpBase* op, const VarBasePtrMap& inputs,
                                     const VarBasePtrMap& outputs,
                                     framework::BlockDesc* block,
                                     const platform::Place expected_place,
                                     const bool stop_gradient) {
+#ifdef WITH_GPERFTOOLS
+  if (gTracerProfilerStarted) {
+    ProfilerFlush();
+  }
+#endif
+
   std::map<std::string, VarBase*> vars;
 
   framework::OpDesc* op_desc = op->op_desc_;

paddle/fluid/imperative/tracer.h

@@ -40,7 +40,7 @@ platform::Place GetExpectedPlace(platform::Place place, VarBasePtrMap inputs);
 
 class Tracer {
  public:
-  explicit Tracer(framework::BlockDesc* root_block) : root_block_(root_block) {}
+  explicit Tracer(framework::BlockDesc* root_block);
 
   virtual ~Tracer() {}