overlap rpc op memcpy in distributed training

paddle/fluid/framework/details/multi_devices_graph_builder.cc

@@ -191,15 +191,54 @@ std::unique_ptr<SSAGraph> MultiDevSSAGraphBuilder::Build(
   };
 
   bool is_forwarding = true;
+  std::unordered_map<std::string, int> rpc_var_device_mapping;
+  int rpc_op_device_id = 0;
+  auto schedule_rpc_op = [&]() -> void {
+    rpc_op_device_id++;
+    if (rpc_op_device_id >= static_cast<int>(places_.size())) {
+      rpc_op_device_id = 0;
+    }
+  };
+
   for (auto *op : program.Block(0).AllOps()) {
     if (boost::get<int>(
             op->GetAttr(OpProtoAndCheckerMaker::OpRoleAttrName())) ==
         static_cast<int>(OpRole::kRPC)) {
       // append rpc op if program is distributed trainer main program.
       // always use the first device
-      CreateRPCOp(&result, *op);
+      if (op->Type() == "send_vars") {
+        auto got = remote_vars_devices_.find(op->InputArgumentNames()[0]);
+        if (got == remote_vars_devices_.end()) {
+          schedule_rpc_op();
+        } else {
+          rpc_op_device_id = got->second;
+        }
+        CreateRPCOp(&result, *op, rpc_op_device_id);
+      } else if (op->Type() == "recv") {
+        schedule_rpc_op();
+        for (auto &varname : op->OutputArgumentNames()) {
+          remote_vars_devices_.insert({varname, rpc_op_device_id});
+        }
+        CreateRPCOp(&result, *op, rpc_op_device_id);
+      } else {
+        CreateRPCOp(&result, *op, 0);
+      }
     } else if (IsDistTrainOp(*op, send_vars, recv_vars)) {
-      CreateDistTrainOp(&result, *op);
+      if (op->Type() == "split_byref") {
+        schedule_rpc_op();
+        for (auto &varname : op->OutputArgumentNames()) {
+          remote_vars_devices_.insert({varname, rpc_op_device_id});
+        }
+        CreateDistTrainOp(&result, *op, rpc_op_device_id);
+      }
+      if (op->Type() == "oncat") {
+        auto got = remote_vars_devices_.find(op->InputArgumentNames()[0]);
+        PADDLE_ENFORCE_NE(got != remote_vars_devices_.end(),
+                          "can not find right place to concat received var.");
+        CreateDistTrainOp(&result, *op, got->second);
+      } else {
+        CreateDistTrainOp(&result, *op, 0);
+      }
     } else if (IsScaleLossOp(*op)) {
       // user can customize loss@grad if not use_default_grad_scale_
       if (strategy_.gradient_scale_ !=
@@ -464,17 +503,18 @@ void MultiDevSSAGraphBuilder::ConnectOp(SSAGraph *result, OpHandleBase *op,
 }
 
 void MultiDevSSAGraphBuilder::CreateDistTrainOp(SSAGraph *result,
-                                                const OpDesc &op) const {
-  CreateComputationalOp(result, op, 0);
+                                                const OpDesc &op,
+                                                int place_id) const {
+  CreateComputationalOp(result, op, place_id);
   if (op.Type() == "concat") {
     ConnectOp(result, result->ops_.back().get(), "fetch_barrier");
   }
 }
 
-void MultiDevSSAGraphBuilder::CreateRPCOp(SSAGraph *result,
-                                          const OpDesc &op) const {
-  auto &p = places_[0];
-  auto *s = local_scopes_[0];
+void MultiDevSSAGraphBuilder::CreateRPCOp(SSAGraph *result, const OpDesc &op,
+                                          int place_id) const {
+  auto &p = places_[place_id];
+  auto *s = local_scopes_[place_id];
   result->ops_.emplace_back(new RPCOpHandle(op, s, p, op.Type()));
 
   if (op.Type() == "send_barrier") {
@@ -493,7 +533,7 @@ void MultiDevSSAGraphBuilder::CreateRPCOp(SSAGraph *result,
 
   // TODO(Yancey1989): schedule rpc op on different place may
   // increate throughput
-  CreateOpHandleIOs(result, op, 0);
+  CreateOpHandleIOs(result, op, place_id);
 }
 
 bool MultiDevSSAGraphBuilder::IsScaleLossOp(const OpDesc &op) const {

paddle/fluid/framework/details/multi_devices_graph_builder.h

@@ -48,6 +48,14 @@ class MultiDevSSAGraphBuilder : public SSAGraphBuilder {
 
   std::unique_ptr<SSAGraph> Build(const ProgramDesc &program) const override;
 
+  int GetRemoteVarDevice(const std::string &var_name) const {
+    auto got = remote_vars_devices_.find(var_name);
+    if (got != remote_vars_devices_.end()) {
+      return got->second;
+    }
+    return -1;
+  }
+
  private:
   void CreateOpHandleIOs(SSAGraph *result, const OpDesc &op,
                          size_t place_id) const;
@@ -64,8 +72,9 @@ class MultiDevSSAGraphBuilder : public SSAGraphBuilder {
 
   bool IsScaleLossOp(const OpDesc &op) const;
 
-  void CreateRPCOp(SSAGraph *result, const OpDesc &op) const;
-  void CreateDistTrainOp(SSAGraph *result, const OpDesc &op) const;
+  void CreateRPCOp(SSAGraph *result, const OpDesc &op, int place_id) const;
+  void CreateDistTrainOp(SSAGraph *result, const OpDesc &op,
+                         int place_id) const;
 
   /**
    * Is this operator as the end-point operator before/after send operator.
@@ -111,6 +120,7 @@ class MultiDevSSAGraphBuilder : public SSAGraphBuilder {
 
  private:
   BuildStrategy strategy_;
+  mutable std::unordered_map<std::string, int> remote_vars_devices_;
 };
 }  // namespace details
 }  // namespace framework

paddle/fluid/framework/parallel_executor.cc

@@ -22,7 +22,6 @@ limitations under the License. */
 #include "paddle/fluid/platform/nccl_helper.h"
 #endif
 
-#include "paddle/fluid/framework/details/multi_devices_graph_builder.h"
 #include "paddle/fluid/framework/details/threaded_ssa_graph_executor.h"
 #include "paddle/fluid/platform/profiler.h"
 
@@ -97,15 +96,17 @@ ParallelExecutor::ParallelExecutor(
 // Step 2. Convert main_program to SSA form and dependency graph. Also, insert
 // ncclOp
 #ifdef PADDLE_WITH_CUDA
-  details::MultiDevSSAGraphBuilder builder(
+  builder_.reset(new details::MultiDevSSAGraphBuilder(
       member_->places_, loss_var_name, params, member_->local_scopes_,
-      member_->nccl_ctxs_.get(), build_strategy);
+      member_->nccl_ctxs_.get(), build_strategy));
+
 #else
-  details::MultiDevSSAGraphBuilder builder(member_->places_, loss_var_name,
-                                           params, member_->local_scopes_,
-                                           build_strategy);
+  builder_.reset(new details::MultiDevSSAGraphBuilder(
+      member_->places_, loss_var_name, params, member_->local_scope_,
+      build_strategy));
+
 #endif
-  auto graph = builder.Build(main_program);
+  auto graph = builder_.get()->Build(main_program);
 
   member_->executor_.reset(new details::ThreadedSSAGraphExecutor(
       exec_strategy, member_->local_scopes_, places, std::move(graph)));
@@ -146,8 +147,16 @@ void ParallelExecutor::BCastParamsToGPUs(
           buffer = t->mutable_data(place, main_tensor.type());
         }
         auto &nccl_ctx = member_->nccl_ctxs_->at(place);
-        platform::dynload::ncclBcast(buffer, numel, data_type, 0,
-                                     nccl_ctx.comm_, nccl_ctx.stream());
+
+        if (builder_.get() != nullptr &&
+            builder_->GetRemoteVarDevice(var) != -1) {
+          int place_id = builder_->GetRemoteVarDevice(var);
+          platform::dynload::ncclBcast(buffer, numel, data_type, place_id,
+                                       nccl_ctx.comm_, nccl_ctx.stream());
+        } else {
+          platform::dynload::ncclBcast(buffer, numel, data_type, 0,
+                                       nccl_ctx.comm_, nccl_ctx.stream());
+        }
       }
     } else {
       platform::CPUPlace cpu;

paddle/fluid/framework/parallel_executor.h

@@ -19,12 +19,14 @@ limitations under the License. */
 #include <unordered_set>
 #include <vector>
 #include "paddle/fluid/framework/details/execution_strategy.h"
+#include "paddle/fluid/framework/details/multi_devices_graph_builder.h"
 #include "paddle/fluid/framework/executor.h"
 #include "paddle/fluid/framework/op_info.h"
 #include "paddle/fluid/framework/program_desc.h"
 #include "paddle/fluid/framework/scope.h"
 #include "paddle/fluid/framework/tensor.h"
 #include "paddle/fluid/platform/device_context.h"
+
 namespace paddle {
 namespace framework {
 
@@ -68,6 +70,7 @@ class ParallelExecutor {
 
  private:
   ParallelExecutorPrivate *member_;
+  std::unique_ptr<details::MultiDevSSAGraphBuilder> builder_;
 };
 
 }  // namespace framework