From 1fdf8853d420e884db8a71b47a707889e494d4df Mon Sep 17 00:00:00 2001
From: Yang Yu <yuyang18@baidu.com>
Date: Mon, 25 Dec 2017 14:35:28 +0800
Subject: [PATCH] Optimize adam_op

---
 paddle/operators/adam_op.h  | 32 +++++++-------
 paddle/platform/for_range.h | 85 +++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+), 16 deletions(-)
 create mode 100644 paddle/platform/for_range.h

diff --git a/paddle/operators/adam_op.h b/paddle/operators/adam_op.h
index 887258530cb..c4e2c8bb88e 100644
--- a/paddle/operators/adam_op.h
+++ b/paddle/operators/adam_op.h
@@ -16,7 +16,7 @@ limitations under the License. */
 #include <math.h>  // for sqrt in CPU and CUDA
 #include "paddle/framework/op_registry.h"
 #include "paddle/operators/detail/safe_ref.h"
-#include "paddle/platform/transform.h"
+#include "paddle/platform/for_range.h"
 
 namespace paddle {
 namespace operators {
@@ -36,10 +36,12 @@ struct AdamFunctor {
   const T* lr_;
   const T* grad_;
   const T* param_;
+  T* param_out_;
 
   AdamFunctor(T beta1, T beta2, T epsilon, const T* beta1_pow,
               const T* beta2_pow, const T* mom1, T* mom1_out, const T* mom2,
-              T* mom2_out, const T* lr, const T* grad, const T* param)
+              T* mom2_out, const T* lr, const T* grad, const T* param,
+              T* param_out)
       : beta1_(beta1),
         beta2_(beta2),
         epsilon_(epsilon),
@@ -51,11 +53,10 @@ struct AdamFunctor {
         moment2_out_(mom2_out),
         lr_(lr),
         grad_(grad),
-        param_(param) {}
+        param_(param),
+        param_out_(param_out) {}
 
-  // From param[i] --> param_out[i];
-  inline HOSTDEVICE T operator()(const T& p) const {
-    size_t i = &p - param_;
+  inline HOSTDEVICE void operator()(size_t i) const {
     // Merge all memory access together.
     T g = grad_[i];
     T mom1 = moment1_[i];
@@ -63,17 +64,18 @@ struct AdamFunctor {
     T lr = *lr_;
     T beta1_pow = *beta1_pow_;
     T beta2_pow = *beta2_pow_;
+    T p = param_[i];
 
     // Calculation
-    lr = lr * sqrt(1 - beta2_pow) / (1 - beta1_pow);
+    lr *= sqrt(1 - beta2_pow) / (1 - beta1_pow);
     mom1 = beta1_ * mom1 + (1 - beta1_) * g;
     mom2 = beta2_ * mom2 + (1 - beta2_) * g * g;
-    T new_p = p - lr * (mom1 / (sqrt(mom2) + epsilon_));
+    p -= lr * (mom1 / (sqrt(mom2) + epsilon_));
 
     // Write back to global memory
     moment1_out_[i] = mom1;
     moment2_out_[i] = mom2;
-    return new_p;
+    param_out_[i] = p;
   }
 };
 
@@ -113,13 +115,11 @@ class AdamOpKernel : public framework::OpKernel<T> {
                            mom2.template data<T>(),
                            mom2_out.template mutable_data<T>(ctx.GetPlace()),
                            lr.template data<T>(), grad.template data<T>(),
-                           param.template data<T>());
-
-    const T* in_ptr = param.template data<T>();
-    T* out_ptr = param_out.template mutable_data<T>(ctx.GetPlace());
-    platform::Transform<DeviceContext> trans;
-    trans(static_cast<const DeviceContext&>(ctx.device_context()), in_ptr,
-          in_ptr + param_out.numel(), out_ptr, functor);
+                           param.template data<T>(),
+                           param_out.template mutable_data<T>(ctx.GetPlace()));
+    platform::ForRange<DeviceContext> for_range(
+        static_cast<const DeviceContext&>(ctx.device_context()), param.numel());
+    for_range(functor);
   }
 };
 
diff --git a/paddle/platform/for_range.h b/paddle/platform/for_range.h
new file mode 100644
index 00000000000..6ba6b010761
--- /dev/null
+++ b/paddle/platform/for_range.h
@@ -0,0 +1,85 @@
+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserved.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License. */
+
+#pragma once
+#include "paddle/platform/device_context.h"
+
+namespace paddle {
+namespace platform {
+
+template <typename DeviceContext>
+struct ForRange {
+  ForRange(const DeviceContext& dev_ctx, size_t limit);
+
+  template <typename Function>
+  void operator()(Function func) const;
+};
+
+template <>
+struct ForRange<CPUDeviceContext> {
+  ForRange(const CPUDeviceContext& dev_ctx, size_t limit) : limit_(limit) {}
+
+  template <typename Function>
+  void operator()(Function func) const {
+    for (size_t i = 0; i < limit_; ++i) {
+      func(i);
+    }
+  }
+
+  size_t limit_;
+};
+
+#ifdef __NVCC__
+template <typename Function>
+__global__ static void ForRangeElemwiseOpGridIsOne(Function func) {
+  size_t idx = static_cast<size_t>(threadIdx.x);
+  func(idx);
+}
+
+template <typename Function>
+__global__ static void ForRangeElemwiseOp(Function func, int limit) {
+  size_t idx = static_cast<size_t>(blockIdx.x * blockDim.x + threadIdx.x);
+  if (idx < limit) {
+    func(idx);
+  }
+}
+
+template <>
+struct ForRange<CUDADeviceContext> {
+  ForRange(const CUDADeviceContext& dev_ctx, size_t limit)
+      : dev_ctx_(dev_ctx), limit_(static_cast<int>(limit)) {}
+
+  template <typename Function>
+  inline void operator()(Function func) const {
+    constexpr size_t num_threads = 1024;
+    int block_size = limit_ <= num_threads ? limit_ : num_threads;
+    int grid_size = (limit_ + num_threads - 1) / num_threads;
+
+    if (grid_size == 1) {
+      ForRangeElemwiseOpGridIsOne<<<1, block_size, 0, dev_ctx_.stream()>>>(
+          func);
+    } else {
+      ForRangeElemwiseOp<<<grid_size, block_size, 0, dev_ctx_.stream()>>>(
+          func, limit_);
+    }
+  }
+
+  const CUDADeviceContext& dev_ctx_;
+  int limit_;
+};
+
+#endif
+
+}  // namespace platform
+}  // namespace paddle
-- 
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