Update the demo code and the doc of varbase.backward. (#26506)

* update the demo code and the doc of varbase.backward.

* update the doc of the fake interface `paddle.fluid.Variable`.

* remove BackwardStrategy.

Author: wzzju

paddle/fluid/imperative/backward_strategy.h

@@ -30,12 +30,13 @@
 #include "paddle/fluid/operators/math/math_function.h"
 #include "paddle/fluid/platform/profiler.h"
 
+DECLARE_bool(sort_sum_gradient);
+
 namespace paddle {
 namespace imperative {
 
-void BasicEngine::Init(VarBase* var, const detail::BackwardStrategy& strategy,
-                       bool retain_graph) {
-  backward_strategy_ = strategy;
+void BasicEngine::Init(VarBase* var, bool retain_graph) {
+  sorted_sum_gradient_ = FLAGS_sort_sum_gradient;
   retain_graph_ = retain_graph;
   init_node_ = var->GradVarBase()->GradNode();
   var->GradVarBase()->ClearGradNode();
@@ -105,7 +106,7 @@ void BasicEngine::PrepareGradAccumulators(const OpBase& op) {
 
       auto& accumulator = accumulators_[var.get()];
       if (!accumulator) {
-        if (backward_strategy_.sorted_sum_gradient_) {
+        if (sorted_sum_gradient_) {
           accumulator.reset(new SortedGradientAccumulator(var.get()));
         } else {
           accumulator.reset(new EagerGradientAccumulator(var.get()));

paddle/fluid/imperative/basic_engine.cc

@@ -18,7 +18,6 @@
 #include <unordered_map>
 #include <utility>
 #include <vector>
-#include "paddle/fluid/imperative/backward_strategy.h"
 #include "paddle/fluid/imperative/engine.h"
 #include "paddle/fluid/imperative/gradient_accumulator.h"
 
@@ -30,8 +29,7 @@ class OpBase;
 
 class BasicEngine : public Engine {
  public:
-  void Init(VarBase* var, const detail::BackwardStrategy& strategy,
-            bool retain_graph = false);
+  void Init(VarBase* var, bool retain_graph = false);
 
   void Execute() override;
 
@@ -46,7 +44,7 @@ class BasicEngine : public Engine {
 
  private:
   std::shared_ptr<GradOpNode> init_node_;
-  detail::BackwardStrategy backward_strategy_;
+  bool sorted_sum_gradient_;
   std::unordered_map<GradOpNode*, size_t> node_deps_;
   std::unordered_map<VariableWrapper*, std::unique_ptr<GradientAccumulator>>
       accumulators_;

paddle/fluid/imperative/basic_engine.h

@@ -33,6 +33,8 @@
 #include "paddle/fluid/platform/profiler.h"
 #include "paddle/fluid/string/string_helper.h"
 
+DECLARE_bool(sort_sum_gradient);
+
 namespace paddle {
 namespace imperative {
 
@@ -529,8 +531,7 @@ class PartialGradTask {
                   const std::vector<std::shared_ptr<VarBase>> &output_targets,
                   const std::vector<std::shared_ptr<VarBase>> &output_grads,
                   const std::vector<std::shared_ptr<VarBase>> &no_grad_vars,
-                  const platform::Place &place,
-                  const detail::BackwardStrategy &strategy, bool create_graph,
+                  const platform::Place &place, bool create_graph,
                   bool retain_graph, bool allow_unused, bool only_inputs);
 
   std::vector<std::shared_ptr<VarBase>> Run();
@@ -577,23 +578,22 @@ class PartialGradTask {
   bool retain_graph_;
   bool allow_unused_;
   bool only_inputs_;
-  detail::BackwardStrategy strategy_;
+  bool sorted_sum_gradient_{FLAGS_sort_sum_gradient};
 };
 
 PartialGradTask::PartialGradTask(
     const std::vector<std::shared_ptr<VarBase>> &input_targets,
     const std::vector<std::shared_ptr<VarBase>> &output_targets,
     const std::vector<std::shared_ptr<VarBase>> &output_grads,
     const std::vector<std::shared_ptr<VarBase>> &no_grad_vars,
-    const platform::Place &place, const detail::BackwardStrategy &strategy,
-    bool create_graph, bool retain_graph, bool allow_unused, bool only_inputs) {
+    const platform::Place &place, bool create_graph, bool retain_graph,
+    bool allow_unused, bool only_inputs) {
   input_targets_ = input_targets;
   place_ = place;
   create_graph_ = create_graph;
   retain_graph_ = retain_graph;
   allow_unused_ = allow_unused;
   only_inputs_ = only_inputs;
-  strategy_ = strategy;
 
   PADDLE_ENFORCE_EQ(only_inputs_, true,
                     platform::errors::Unimplemented(
@@ -981,7 +981,7 @@ void PartialGradTask::PrepareInitialGradientAccumulators(const OpBase *op) {
 
       if (!accumulator) {
         accumulator.reset(new GradientAccumulationInfo(
-            var, strategy_.sorted_sum_gradient_, create_graph_));
+            var, sorted_sum_gradient_, create_graph_));
       }
 
       accumulator->IncreaseTotalRefCnt();
@@ -1033,11 +1033,11 @@ PartialGradEngine::PartialGradEngine(
     const std::vector<std::shared_ptr<VarBase>> &output_targets,
     const std::vector<std::shared_ptr<VarBase>> &output_grads,
     const std::vector<std::shared_ptr<VarBase>> &no_grad_vars,
-    const platform::Place &place, const detail::BackwardStrategy &strategy,
-    bool create_graph, bool retain_graph, bool allow_unused, bool only_inputs)
+    const platform::Place &place, bool create_graph, bool retain_graph,
+    bool allow_unused, bool only_inputs)
     : task_(new PartialGradTask(input_targets, output_targets, output_grads,
-                                no_grad_vars, place, strategy, create_graph,
-                                retain_graph, allow_unused, only_inputs)) {}
+                                no_grad_vars, place, create_graph, retain_graph,
+                                allow_unused, only_inputs)) {}
 
 PartialGradEngine::~PartialGradEngine() { Clear(); }
 

paddle/fluid/imperative/partial_grad_engine.cc

@@ -16,7 +16,6 @@
 
 #include <memory>
 #include <vector>
-#include "paddle/fluid/imperative/backward_strategy.h"
 #include "paddle/fluid/imperative/engine.h"
 #include "paddle/fluid/platform/place.h"
 
@@ -33,8 +32,7 @@ class PartialGradEngine : public Engine {
                     const std::vector<std::shared_ptr<VarBase>> &output_targets,
                     const std::vector<std::shared_ptr<VarBase>> &output_grads,
                     const std::vector<std::shared_ptr<VarBase>> &no_grad_vars,
-                    const platform::Place &place,
-                    const detail::BackwardStrategy &strategy, bool create_graph,
+                    const platform::Place &place, bool create_graph,
                     bool retain_graph, bool allow_unused, bool only_inputs);
 
   ~PartialGradEngine();

paddle/fluid/imperative/partial_grad_engine.h

@@ -240,9 +240,8 @@ TEST(test_tracer, test_trace_op_with_multi_device_inputs) {
   framework::AttributeMap reduce_attr_map;
   tracer.TraceOp("reduce_sum", reduce_in, reduce_out, reduce_attr_map,
                  gpu_place, true);
-  detail::BackwardStrategy back_st;
   imperative::BasicEngine engine;
-  engine.Init(reduce_sum_out.get(), back_st);
+  engine.Init(reduce_sum_out.get());
   engine.Execute();
 
   framework::LoDTensor rlt;
@@ -356,9 +355,8 @@ TEST(test_tracer, test_var_without_grad_var) {
   ASSERT_EQ(y_in->GradVarBase()->GradOpNum(), 0UL);
   ASSERT_EQ(vout->GradVarBase()->GradOpNum(), 1UL);
 
-  detail::BackwardStrategy back_st;
   imperative::BasicEngine engine;
-  engine.Init(vout.get(), back_st);
+  engine.Init(vout.get());
   engine.Execute();
 
   // check the grad

paddle/fluid/imperative/tests/test_tracer.cc

@@ -508,3 +508,16 @@ DEFINE_int32(
     "summary will be shown."
     "If FLAGS_call_stack_level == 2, the python stack, c++ stack, and "
     "error message summary will be shown.");
+
+/**
+ * Debug related FLAG
+ * Name: sort_sum_gradient
+ * Since Version: 2.0.0
+ * Value Range: bool, default=false
+ * Example:
+ * Note: If True, gradients are summed by the reverse order of
+ * the forward execution sequence.
+ */
+DEFINE_bool(sort_sum_gradient, false,
+            "Sum gradients by the reverse order of "
+            "the forward execution sequence.");

paddle/fluid/platform/flags.cc

@@ -38,6 +38,7 @@ DECLARE_bool(enable_rpc_profiler);
 DECLARE_int32(multiple_of_cupti_buffer_size);
 DECLARE_bool(reader_queue_speed_test_mode);
 DECLARE_int32(call_stack_level);
+DECLARE_bool(sort_sum_gradient);
 // device management
 DECLARE_int32(paddle_num_threads);
 // executor
@@ -340,7 +341,7 @@ static void RegisterGlobalVarGetterSetter() {
   REGISTER_PUBLIC_GLOBAL_VAR(
       FLAGS_eager_delete_tensor_gb, FLAGS_enable_parallel_graph,
       FLAGS_allocator_strategy, FLAGS_use_system_allocator, FLAGS_check_nan_inf,
-      FLAGS_call_stack_level, FLAGS_cpu_deterministic,
+      FLAGS_call_stack_level, FLAGS_sort_sum_gradient, FLAGS_cpu_deterministic,
       FLAGS_enable_rpc_profiler, FLAGS_multiple_of_cupti_buffer_size,
       FLAGS_reader_queue_speed_test_mode, FLAGS_pe_profile_fname,
       FLAGS_print_sub_graph_dir, FLAGS_fraction_of_cpu_memory_to_use,

paddle/fluid/pybind/global_value_getter_setter.cc

@@ -30,7 +30,6 @@ limitations under the License. */
 
 #include "paddle/fluid/imperative/all_reduce.h"
 #include "paddle/fluid/imperative/amp_auto_cast.h"
-#include "paddle/fluid/imperative/backward_strategy.h"
 #include "paddle/fluid/imperative/basic_engine.h"
 #include "paddle/fluid/imperative/data_loader.h"
 #include "paddle/fluid/imperative/layer.h"
@@ -507,50 +506,6 @@ void BindImperative(py::module *m_ptr) {
         []() { memory::allocation::MemoryMapFdSet::Instance().Clear(); });
 #endif
 
-  py::class_<imperative::detail::BackwardStrategy> backward_strategy(
-      m, "BackwardStrategy", R"DOC(
-
-    BackwardStrategy is a descriptor of how to run the backward process.
-
-    **Note**:
-        **This API is only available in** `Dygraph <../../user_guides/howto/dygraph/DyGraph.html>`_ **Mode**
-
-    Attribute:
-        **sort_sum_gradient**:
-
-        If framework will sum the gradient by the reverse order of trace. eg. x_var ( :ref:`api_guide_Variable` ) will be the input of multiple OP such as :ref:`api_fluid_layers_scale` , this attr will decide if framework will sum gradient of `x_var` by the reverse order.
-
-        By Default: False
-
-        Examples:
-            .. code-block:: python
-
-                import numpy as np
-                import paddle.fluid as fluid
-
-                x = np.ones([2, 2], np.float32)
-                with fluid.dygraph.guard():
-                    x_var = fluid.dygraph.to_variable(x)
-                    sums_inputs = []
-                    # x_var will be multi-scales' input here
-                    for _ in range(10):
-                        sums_inputs.append(fluid.layers.scale(x_var))
-                    ret2 = fluid.layers.sums(sums_inputs)
-                    loss2 = fluid.layers.reduce_sum(ret2)
-                    backward_strategy = fluid.dygraph.BackwardStrategy()
-                    backward_strategy.sort_sum_gradient = True
-                    loss2.backward(backward_strategy)
-      )DOC");
-  backward_strategy.def(py::init())
-      .def_property("sort_sum_gradient",
-                    [](const imperative::detail::BackwardStrategy &self) {
-                      return self.sorted_sum_gradient_;
-                    },
-                    [](imperative::detail::BackwardStrategy &self,
-                       bool sorted_sum_gradient) {
-                      self.sorted_sum_gradient_ = sorted_sum_gradient;
-                    });
-
   m.def("start_imperative_gperf_profiler",
         []() { imperative::StartProfile(); });
 
@@ -745,21 +700,18 @@ void BindImperative(py::module *m_ptr) {
                          inputs2.append(tmp)
                     ret2 = fluid.layers.sums(inputs2)
                     loss2 = fluid.layers.reduce_sum(ret2)
-                    backward_strategy = fluid.dygraph.BackwardStrategy()
-                    backward_strategy.sort_sum_gradient = True
-                    loss2.backward(backward_strategy)
+                    loss2.backward()
                     print(loss2.gradient())
                     loss2.clear_gradient()
                     print("After clear {}".format(loss2.gradient()))
       )DOC")
       .def("_run_backward",
-           [](imperative::VarBase &self,
-              const imperative::detail::BackwardStrategy &bckst,
-              const imperative::Tracer &tracer, bool retain_graph) {
+           [](imperative::VarBase &self, const imperative::Tracer &tracer,
+              bool retain_graph) {
              // TODO(jiabin): when we impl more backward execution we can
              // select them
              auto *engine = tracer.GetEngine();
-             engine->Init(&self, bckst, retain_graph);
+             engine->Init(&self, retain_graph);
              VLOG(3) << "Start backward";
              engine->Execute();
              VLOG(3) << "Finish backward";
@@ -1024,13 +976,11 @@ void BindImperative(py::module *m_ptr) {
              &output_targets,
          const std::vector<std::shared_ptr<imperative::VarBase>> &output_grads,
          const std::vector<std::shared_ptr<imperative::VarBase>> &no_grad_vars,
-         const platform::Place &place,
-         const imperative::detail::BackwardStrategy &strategy,
-         bool create_graph, bool retain_graph, bool allow_unused,
-         bool only_inputs) {
+         const platform::Place &place, bool create_graph, bool retain_graph,
+         bool allow_unused, bool only_inputs) {
         imperative::PartialGradEngine engine(
             input_targets, output_targets, output_grads, no_grad_vars, place,
-            strategy, create_graph, retain_graph, allow_unused, only_inputs);
+            create_graph, retain_graph, allow_unused, only_inputs);
         engine.Execute();
         return engine.GetResult();
       },

paddle/fluid/pybind/imperative.cc

@@ -225,7 +225,6 @@
 from .framework import CUDAPlace  #DEFINE_ALIAS
 from .framework import CUDAPinnedPlace  #DEFINE_ALIAS
 
-from .framework import BackwardStrategy  #DEFINE_ALIAS
 from .framework import to_variable  #DEFINE_ALIAS
 from .framework import grad  #DEFINE_ALIAS
 from .framework import no_grad  #DEFINE_ALIAS