From 9012787f95004409d721dcfc40a95b6698234a3a Mon Sep 17 00:00:00 2001
From: carryyu <569782149@qq.com>
Date: Thu, 29 Sep 2022 20:45:56 +0800
Subject: [PATCH] Optimize softmax's performance when dim_size >= 100000.
 (#46535)

---
 paddle/phi/kernels/gpudnn/softmax_gpudnn.h | 236 ++++++++++++++++++++-
 1 file changed, 235 insertions(+), 1 deletion(-)

diff --git a/paddle/phi/kernels/gpudnn/softmax_gpudnn.h b/paddle/phi/kernels/gpudnn/softmax_gpudnn.h
index a15244cc52..75dfc8514a 100644
--- a/paddle/phi/kernels/gpudnn/softmax_gpudnn.h
+++ b/paddle/phi/kernels/gpudnn/softmax_gpudnn.h
@@ -19,6 +19,7 @@ limitations under the License. */
 #include "paddle/phi/common/bfloat16.h"
 #include "paddle/phi/common/float16.h"
 #include "paddle/phi/core/dense_tensor.h"
+#include "paddle/phi/kernels/funcs/aligned_vector.h"
 #include "paddle/phi/kernels/funcs/axis_utils.h"
 #include "paddle/phi/kernels/primitive/kernel_primitives.h"
 
@@ -26,6 +27,32 @@ limitations under the License. */
 #include "paddle/fluid/platform/device/gpu/gpu_device_function.h"
 #include "paddle/fluid/platform/device/gpu/gpu_dnn.h"
 
+#define MATRIX_SOFTMAX_ALIGN_BYTES 16
+#define MATRIX_SOFTMAX_THREAHOLD 100000
+
+#define FIXED_BLOCK_DIM_BASE(dim, ...) \
+  case (dim): {                        \
+    constexpr auto kBlockDim = (dim);  \
+    __VA_ARGS__;                       \
+  } break
+
+#define FIXED_VEC_SIZE_BASE(vec_size, ...) \
+  case (vec_size): {                       \
+    constexpr auto VecSize = (vec_size);   \
+    __VA_ARGS__;                           \
+  } break
+
+#define FIXED_BLOCK_DIM(...)                \
+  FIXED_BLOCK_DIM_BASE(512, ##__VA_ARGS__); \
+  FIXED_BLOCK_DIM_BASE(256, ##__VA_ARGS__); \
+  FIXED_BLOCK_DIM_BASE(128, ##__VA_ARGS__); \
+  FIXED_BLOCK_DIM_BASE(64, ##__VA_ARGS__);  \
+  FIXED_BLOCK_DIM_BASE(32, ##__VA_ARGS__)
+
+#define FIXED_VEC_SIZE(...)              \
+  FIXED_VEC_SIZE_BASE(8, ##__VA_ARGS__); \
+  FIXED_VEC_SIZE_BASE(4, ##__VA_ARGS__)
+
 namespace phi {
 
 using ScopedTensorDescriptor = paddle::platform::ScopedTensorDescriptor;
@@ -85,6 +112,20 @@ static inline int Log2Ceil(int value) {
   return log2_value;
 }
 
+inline int getBlockSize(int vec_size, uint64_t dim_size) {
+  uint64_t block_size = 1;
+  uint64_t max_block_size =
+      std::min(dim_size / vec_size, static_cast<uint64_t>(1024));
+
+  if (vec_size > 1) {
+    max_block_size /= 2;
+  }
+
+  while (block_size < (max_block_size)) block_size *= 2;
+  block_size = std::max(block_size, static_cast<uint64_t>(32));
+  return block_size;
+}
+
 template <typename T, int BatchSize, int WarpSize>
 __device__ __forceinline__ void WarpReduceSum(T* sum) {
 #pragma unroll
@@ -111,6 +152,41 @@ __device__ __forceinline__ void WarpReduceMax(T* sum) {
   }
 }
 
+template <typename T>
+__inline__ __device__ void BlockReduceMax(T* val) {
+  static __shared__ T shared[32];
+  int lane = threadIdx.x & 0x1f;
+  int wid = threadIdx.x >> 5;
+
+  WarpReduceMax<T, 1, 32>(val);
+
+  if (lane == 0) shared[wid] = *val;
+
+  __syncthreads();
+
+  int block_span = (blockDim.x + warpSize - 1) >> 5;
+  *val = (lane < block_span) ? shared[lane] : -1e10f;
+  WarpReduceMax<T, 1, 32>(val);
+}
+
+template <typename T>
+__inline__ __device__ void BlockReduceSum(T* val) {
+  static __shared__ T shared[32];
+  int lane = threadIdx.x & 0x1f;
+  int wid = threadIdx.x >> 5;
+
+  WarpReduceSum<T, 1, 32>(val);
+
+  __syncthreads();
+  if (lane == 0) shared[wid] = *val;
+
+  __syncthreads();
+
+  int block_span = (blockDim.x + warpSize - 1) >> 5;
+  *val = (lane < block_span) ? shared[lane] : static_cast<T>(0.0f);
+  WarpReduceSum<T, 1, 32>(val);
+}
+
 template <typename Tx, typename Ty = Tx>
 struct ReduceMaxFunctor {
   inline Ty initial() { return -std::numeric_limits<Ty>::infinity(); }
@@ -120,6 +196,14 @@ struct ReduceMaxFunctor {
   }
 };
 
+template <typename T, typename AccT>
+struct MaxFunctor {
+  __device__ __forceinline__ AccT operator()(const AccT& max_v,
+                                             const T& v) const {
+    return max(max_v, static_cast<AccT>(v));
+  }
+};
+
 template <typename Tx, typename Ty = Tx>
 struct ExpFunctor {
   HOSTDEVICE inline Ty operator()(const Tx& x) const {
@@ -245,6 +329,126 @@ struct LogSoftmaxBackwardFunctor {
   Tx sum;
 };
 
+template <typename T, typename AccT>
+struct SumExpFunctor {
+  HOSTDEVICE inline SumExpFunctor(AccT v) : max_v(v) {}
+
+  HOSTDEVICE inline AccT operator()(AccT sum, T v) const {
+    return sum + std::exp(static_cast<AccT>(v) - max_v);
+  }
+
+ private:
+  AccT max_v;
+};
+
+template <template <typename, typename> class Reduction,
+          typename T,
+          typename AccT,
+          int VecSize>
+__device__ __forceinline__ AccT
+ThreadVecReduce(const T* data,
+                int dim_size,
+                const Reduction<T, AccT>& functor,
+                AccT default_value) {
+  using VecT = phi::AlignedVector<T, VecSize>;
+  AccT thread_val = default_value;
+  const int last = dim_size % (VecSize * blockDim.x);
+
+  T v[VecSize];
+  VecT* value = reinterpret_cast<VecT*>(&v);
+
+  for (int offset = threadIdx.x; offset * VecSize < dim_size - last;
+       offset += blockDim.x) {
+    *value = reinterpret_cast<VecT*>(const_cast<T*>(data))[offset];
+#pragma unroll
+    for (int i = 0; i < VecSize; i++) {
+      thread_val = functor(thread_val, v[i]);
+    }
+  }
+
+  for (int offset = dim_size - last + threadIdx.x; offset < dim_size;
+       offset += blockDim.x) {
+    thread_val = functor(thread_val, data[offset]);
+  }
+  return thread_val;
+}
+
+template <template <typename, typename> class Reduction,
+          typename T,
+          typename AccT,
+          int VecSize>
+__device__ __forceinline__ void ThreadVecWrite(T* out,
+                                               const T* input,
+                                               int dim_size,
+                                               Reduction<AccT, T> functor) {
+  using VecT = phi::AlignedVector<T, VecSize>;
+
+  const int last = dim_size % (VecSize * blockDim.x);
+
+  T in_v[VecSize];
+  VecT* in_value = reinterpret_cast<VecT*>(&in_v);
+
+  T out_v[VecSize];
+  VecT* out_value = reinterpret_cast<VecT*>(&out_v);
+
+  for (int offset = threadIdx.x; offset * VecSize < dim_size - last;
+       offset += blockDim.x) {
+    *in_value = reinterpret_cast<VecT*>(const_cast<T*>(input))[offset];
+#pragma unroll
+    for (int i = 0; i < VecSize; i++) {
+      out_v[i] = functor(static_cast<AccT>(in_v[i]));
+    }
+    reinterpret_cast<VecT*>(out)[offset] = *out_value;
+  }
+
+  for (int offset = dim_size - last + threadIdx.x; offset < dim_size;
+       offset += blockDim.x) {
+    out[offset] = functor(static_cast<AccT>(input[offset]));
+  }
+}
+
+template <typename T,
+          typename AccT,
+          typename IndexType,
+          int BatchSize,
+          int VecSize,
+          bool LogMode = false>
+__global__ void KeMatrixSoftmaxForward(T* softmax, const T* src, int dim_size) {
+  using VecT = phi::AlignedVector<T, VecSize>;
+
+  int bid = blockIdx.x;
+  const T* batch_input = src + bid * dim_size;
+  T* batch_output = softmax + bid * dim_size;
+
+  // get max value
+  AccT thread_max = ThreadVecReduce<MaxFunctor, T, AccT, VecSize>(
+      batch_input,
+      dim_size,
+      MaxFunctor<T, AccT>(),
+      std::numeric_limits<AccT>::min());
+  BlockReduceMax<AccT>(&thread_max);
+
+  // get exp value and sum all
+  AccT thread_exp = ThreadVecReduce<SumExpFunctor, T, AccT, VecSize>(
+      batch_input,
+      dim_size,
+      SumExpFunctor<T, AccT>(thread_max),
+      static_cast<AccT>(0.));
+  BlockReduceSum<AccT>(&thread_exp);
+
+  // write data to softmax_output according to the LogMode
+  if (LogMode) {
+    LogSoftmaxForwardFunctor<AccT, T> reduction(thread_max,
+                                                std::log(thread_exp));
+    ThreadVecWrite<LogSoftmaxForwardFunctor, T, AccT, VecSize>(
+        batch_output, batch_input, dim_size, reduction);
+  } else {
+    SoftmaxForwardFunctor<AccT, T> reduction(thread_max, thread_exp);
+    ThreadVecWrite<SoftmaxForwardFunctor, T, AccT, VecSize>(
+        batch_output, batch_input, dim_size, reduction);
+  }
+}
+
 /*
 Core function of computing softmax forward for axis=-1.
 The computation includes
@@ -927,6 +1131,30 @@ void LaunchSoftmaxBackwardCudnnKernel(const GPUContext& dev_ctx,
   }
 }
 
+template <typename T, typename IndexType, bool LogMode>
+void LaunchKeMatrixSoftmaxForwardKernel(
+    const GPUContext& dev_ctx, T* out, const T* input, int N, int dim_size) {
+  using AccT = typename phi::dtype::MPTypeTrait<T>::Type;
+  const int vec_size = MATRIX_SOFTMAX_ALIGN_BYTES / sizeof(T);
+  switch (getBlockSize(vec_size, dim_size)) {
+    FIXED_BLOCK_DIM(switch (vec_size) {
+      FIXED_VEC_SIZE(
+          KeMatrixSoftmaxForward<T,
+                                 AccT,
+                                 IndexType,
+                                 kBlockDim,
+                                 VecSize,
+                                 LogMode>
+          <<<N, kBlockDim, 0, dev_ctx.stream()>>>(out, input, dim_size));
+      default:
+        break;
+    });
+    default:
+      PADDLE_THROW(
+          errors::Fatal("the input dim has error in the softmax cuda kernel."));
+  }
+}
+
 #if CUDNN_VERSION < 8100
 template <>
 inline void LaunchSoftmaxForwardCudnnKernel<phi::dtype::bfloat16>(
@@ -967,7 +1195,8 @@ bool UseCudnnSoftmax(const GPUContext& ctx,
   }
   constexpr int max_dim = 512;
   if (!cudnn_available || !last_dim ||
-      (softmax_dim <= max_dim && sizeof(T) <= 4)) {
+      (softmax_dim <= max_dim && sizeof(T) <= 4) ||
+      softmax_dim >= MATRIX_SOFTMAX_THREAHOLD) {
     return false;
   } else {
     return true;
@@ -991,6 +1220,11 @@ void SoftmaxForwardCUDAKernelDriverImpl(const GPUContext& dev_ctx,
 
   if (D == 1) {
     if (!UseCudnnSoftmax<T>(dev_ctx, dim, true)) {
+      if (dim >= MATRIX_SOFTMAX_THREAHOLD) {
+        LaunchKeMatrixSoftmaxForwardKernel<T, IndexType, LogMode>(
+            dev_ctx, out_data, x.data<T>(), N, dim);
+        return;
+      }
       int dim_log2 = static_cast<int>(Log2Ceil(dim));
       IndexType dim_ceil = 1 << dim_log2;
       int warp_size = (dim_ceil < 32) ? dim_ceil : 32;
-- 
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