improve dropout (#29465)

* improve drop out

* add VectorizedRandomGeneratorWithGenerator

* fix bug

* modify according to comments

paddle/fluid/operators/dropout_op.cu

@@ -17,6 +17,7 @@ limitations under the License. */
 #include <thrust/iterator/counting_iterator.h>
 #include <thrust/random.h>
 #include <thrust/transform.h>
+#include <algorithm>
 #include <string>
 #include "paddle/fluid/memory/memcpy.h"
 #include "paddle/fluid/operators/dropout_op.h"
@@ -26,60 +27,35 @@ limitations under the License. */
 namespace paddle {
 namespace operators {
 
-template <typename T, typename MaskType>
-__global__ void RandomGenerator(const size_t n, const int seed,
-                                const float dropout_prob, const T* src,
-                                MaskType* mask_data, T* dst,
-                                bool is_upscale_in_train) {
-  curandStatePhilox4_32_10_t state;
-  int idx = blockDim.x * blockIdx.x + threadIdx.x;
-  int step_size = 0;
+// aligned vector generates vectorized load/store on CUDA
+template <typename T, int Size>
+struct alignas(sizeof(T) * Size) AlignedVector {
+  T val[Size];
+};
 
-  MaskType mask;
-  T dest;
-  for (; idx < n; idx += blockDim.x * gridDim.x) {
-    T s = src[idx];
-    if (step_size == 0) {
-      curand_init(seed, idx, idx, &state);
-      step_size = blockDim.x * gridDim.x;
-    } else {
-      curand_init(seed, idx, step_size, &state);
-    }
-    if (curand_uniform(&state) < dropout_prob) {
-      mask = 0;
-      dest = 0;
-    } else {
-      mask = 1;
-      if (is_upscale_in_train) {
-        dest = s / static_cast<T>(1.0f - dropout_prob);
-      } else {
-        dest = s;
-      }
-    }
-    mask_data[idx] = mask;
-    dst[idx] = dest;
+template <typename T>
+inline int VectorizedSize(const T* pointer) {
+  uint64_t address = reinterpret_cast<uint64_t>(pointer);
+  constexpr int vec4 = std::alignment_of<AlignedVector<T, 4>>::value;  // NOLINT
+  if (address % vec4 == 0) {
+    return 4;
   }
+  return 1;
 }
 
 template <typename T, typename MaskType>
-__global__ void RandomGeneratorWithSeed(const size_t n, const int* seed,
-                                        const float dropout_prob, const T* src,
-                                        MaskType* mask_data, T* dst,
-                                        bool is_upscale_in_train) {
+__global__ void RandomGenerator(const size_t n, uint64_t seed,
+                                const float dropout_prob, const T* src,
+                                MaskType* mask_data, T* dst,
+                                bool is_upscale_in_train, uint64_t increment) {
   curandStatePhilox4_32_10_t state;
   int idx = blockDim.x * blockIdx.x + threadIdx.x;
-  int step_size = 0;
+  curand_init(seed, idx, increment, &state);
 
   MaskType mask;
   T dest;
   for (; idx < n; idx += blockDim.x * gridDim.x) {
     T s = src[idx];
-    if (step_size == 0) {
-      curand_init(seed[0], idx, idx, &state);
-      step_size = blockDim.x * gridDim.x;
-    } else {
-      curand_init(seed[0], idx, step_size, &state);
-    }
     if (curand_uniform(&state) < dropout_prob) {
       mask = 0;
       dest = 0;
@@ -96,39 +72,49 @@ __global__ void RandomGeneratorWithSeed(const size_t n, const int* seed,
   }
 }
 
-template <typename T, typename MaskType>
-__global__ void RandomGeneratorWithGenerator(const size_t n, uint64_t seed,
-                                             const float dropout_prob,
-                                             const T* src, MaskType* mask_data,
-                                             T* dst, bool is_upscale_in_train,
-                                             uint64_t increment) {
+template <typename T, typename MaskType, int VecSize>
+__global__ void VectorizedRandomGenerator(const size_t n, uint64_t seed,
+                                          const float dropout_prob,
+                                          const T* src, MaskType* mask_data,
+                                          T* dst, bool is_upscale_in_train,
+                                          uint64_t increment) {
+  int64_t idx = blockDim.x * blockIdx.x + threadIdx.x;
   curandStatePhilox4_32_10_t state;
-  int idx = blockDim.x * blockIdx.x + threadIdx.x;
-  int step_size = 0;
+  curand_init(seed, idx, increment, &state);
 
   MaskType mask;
   T dest;
-  for (; idx < n; idx += blockDim.x * gridDim.x) {
-    T s = src[idx];
-    if (step_size == 0) {
-      curand_init(seed, idx, increment, &state);
-      step_size = blockDim.x * gridDim.x;
-    } else {
-      curand_init(seed, idx, increment, &state);
-    }
-    if (curand_uniform(&state) < dropout_prob) {
-      mask = 0;
-      dest = 0;
-    } else {
-      mask = 1;
-      if (is_upscale_in_train) {
-        dest = s / static_cast<T>(1.0f - dropout_prob);
+  using LoadT = AlignedVector<T, VecSize>;
+  using MaskLoadT = AlignedVector<MaskType, VecSize>;
+  T factor = static_cast<T>(1.0f / (1.0f - dropout_prob));
+  for (int i = idx * VecSize; i < n; i += blockDim.x * gridDim.x * VecSize) {
+    T src_vec[VecSize];
+    LoadT* value = reinterpret_cast<LoadT*>(&src_vec);
+    *value = *reinterpret_cast<const LoadT*>(&src[i]);
+    float4 rand = curand_uniform4(&state);
+
+    T dest_vec[VecSize];
+    MaskType mask_vec[VecSize];
+
+#pragma unroll
+    for (int ii = 0; ii < VecSize; ii++) {
+      if ((&rand.x)[ii] < dropout_prob) {
+        dest_vec[ii] = 0;
+        mask_vec[ii] = 0;
       } else {
-        dest = s;
+        if (is_upscale_in_train) {
+          dest_vec[ii] = src_vec[ii] * factor;
+        } else {
+          dest_vec[ii] = src_vec[ii];
+        }
+        mask_vec[ii] = 1;
       }
     }
-    mask_data[idx] = mask;
-    dst[idx] = dest;
+
+    *(reinterpret_cast<LoadT*>(&dst[i])) =
+        *reinterpret_cast<LoadT*>(&dest_vec[0]);
+    *(reinterpret_cast<MaskLoadT*>(&mask_data[i])) =
+        *reinterpret_cast<MaskLoadT*>(&mask_vec[0]);
   }
 }
 
@@ -170,36 +156,57 @@ class GPUDropoutKernel : public framework::OpKernel<T> {
 
       int threads = 512;
       int grid = (x_numel + threads - 1) / threads;
+      const auto& dev_ctx = context.cuda_device_context();
+      int blocks_per_sm =
+          dev_ctx.GetMaxPhysicalThreadCount() / dev_ctx.GetSMCount() / threads;
+      grid = std::min(dev_ctx.GetSMCount() * blocks_per_sm, grid);
+
+      // increment is used to set the args(offset) of curand_init, which defines
+      // offset in subsequence.
+      // The detail:
+      // https://docs.nvidia.com/cuda/curand/device-api-overview.html
+      // Increment should be at least the number of curand() random numbers used
+      // in each thread to avoid the random number generated this time being the
+      // same as the previous calls.
+      uint64_t seed_data;
+      uint64_t increment;
+      int vec_size = VectorizedSize<T>(x_data);
+      auto offset =
+          ((x_numel - 1) / (threads * grid * vec_size) + 1) * vec_size;
+      int device_id = BOOST_GET_CONST(platform::CUDAPlace, context.GetPlace())
+                          .GetDeviceId();
+      auto gen_cuda = framework::GetDefaultCUDAGenerator(device_id);
+
       if (seed && platform::is_gpu_place(seed->place())) {
-        auto seed_gpu_data = seed->data<int>();
-        RandomGeneratorWithSeed<T, uint8_t><<<grid, threads, 0, stream>>>(
-            size, seed_gpu_data, dropout_prob, x_data, mask_data, y_data,
-            upscale_in_train);
-        return;
-      }
-      int seed_data;
-      std::random_device rnd;
-      if (seed) {
-        seed_data = *(seed->data<int>());
+        framework::Tensor seed_cpu_tensor;
+        TensorCopySync(*seed, platform::CPUPlace(), &seed_cpu_tensor);
+        seed_data = static_cast<uint64_t>(seed_cpu_tensor.data<int>()[0]);
+        increment = offset;
+      } else if (gen_cuda->GetIsInitPy() && (!context.Attr<bool>("fix_seed"))) {
+        auto seed_offset = gen_cuda->IncrementOffset(offset);
+        seed_data = seed_offset.first;
+        increment = seed_offset.second;
       } else {
-        seed_data =
-            context.Attr<bool>("fix_seed") ? context.Attr<int>("seed") : rnd();
+        if (seed) {
+          seed_data = *(seed->data<int>());
+        } else {
+          std::random_device rnd;
+          seed_data = context.Attr<bool>("fix_seed") ? context.Attr<int>("seed")
+                                                     : rnd();
+        }
+        increment = offset;
       }
 
-      int device_id = BOOST_GET_CONST(platform::CUDAPlace, context.GetPlace())
-                          .GetDeviceId();
-      auto gen_cuda = framework::GetDefaultCUDAGenerator(device_id);
-      if (gen_cuda->GetIsInitPy() && (!context.Attr<bool>("fix_seed"))) {
-        auto seed_offset = gen_cuda->IncrementOffset(1);
-        RandomGeneratorWithGenerator<T, uint8_t><<<grid, threads, 0, stream>>>(
-            size, seed_offset.first, dropout_prob, x_data, mask_data, y_data,
-            upscale_in_train, seed_offset.second);
-        return;
+      if (vec_size == 4) {
+        VectorizedRandomGenerator<T, uint8_t, 4><<<grid, threads, 0, stream>>>(
+            size, seed_data, dropout_prob, x_data, mask_data, y_data,
+            upscale_in_train, increment);
+      } else {
+        RandomGenerator<T, uint8_t><<<grid, threads, 0, stream>>>(
+            size, seed_data, dropout_prob, x_data, mask_data, y_data,
+            upscale_in_train, increment);
       }
 
-      RandomGenerator<T, uint8_t><<<grid, threads, 0, stream>>>(
-          size, seed_data, dropout_prob, x_data, mask_data, y_data,
-          upscale_in_train);
     } else {
       auto X = EigenMatrix<T>::Reshape(*x, 1);
       auto Y = EigenMatrix<T>::Reshape(*y, 1);