softmax reconstruction and optimization (#31821)

paddle/fluid/operators/softmax_cudnn_op.cu

@@ -13,7 +13,9 @@ See the License for the specific language governing permissions and
 limitations under the License. */
 
 #include "paddle/fluid/framework/op_registry.h"
+#include "paddle/fluid/operators/amp/fp16_type_traits.h"
 #include "paddle/fluid/operators/math/math_cuda_utils.h"
+#include "paddle/fluid/operators/softmax_impl.cuh"
 #include "paddle/fluid/operators/softmax_op.h"
 #include "paddle/fluid/platform/cuda_device_function.h"
 #ifdef PADDLE_WITH_HIP
@@ -21,7 +23,6 @@ limitations under the License. */
 #else
 #include "paddle/fluid/platform/cudnn_helper.h"
 #endif
-#include "paddle/fluid/platform/gpu_launch_config.h"
 
 namespace paddle {
 namespace platform {
@@ -37,288 +38,414 @@ using ScopedTensorDescriptor = platform::ScopedTensorDescriptor;
 using DataLayout = platform::DataLayout;
 using Tensor = framework::Tensor;
 
-#define LAUNCH_SOFTMAX_WARP_FORWARD(Log2Elements)                  \
-  case Log2Elements:                                               \
-    WarpSoftmaxForward<T, float, Log2Elements><<<                  \
-        blocks, threads, 0, ctx.cuda_device_context().stream()>>>( \
-        out_data, x->data<T>(), N, dim, dim);                      \
-    break;
-
-#define LAUNCH_SOFTMAX_WARP_BACKWARD(Log2Elements)                 \
-  case Log2Elements:                                               \
-    softmax_warp_backward<T, float, Log2Elements><<<               \
-        blocks, threads, 0, ctx.cuda_device_context().stream()>>>( \
-        dx_data, mul_grad.data<T>(), out->data<T>(), N, dim, dim); \
-    break;
-
-static inline int SizeOutAxis(const int axis, DDim dims) {
-  int size = 1;
-  for (int i = axis + 1; i < dims.size(); i++) {
-    size *= dims[i];
-  }
-  return size;
-}
-
-int log2_ceil(int value) {
-  int log2_value = 0;
-  while ((1 << log2_value) < value) ++log2_value;
-  return log2_value;
-}
-
-template <typename T, int VLEN>
-union vec_t {
-  static_assert(sizeof(T) == -1, "vec_t is only available by specialization.");
+// Vectorization trait 4 * sizeof(T)
+template <typename T>
+class VecT4 {};
+template <>
+class VecT4<double> {
+ public:
+  using Type = long4;
 };
-
 template <>
-union vec_t<float, 4> {
-  float4 s;
-  float v[4];
+class VecT4<float> {
+ public:
+  using Type = int4;
+};
+template <>
+class VecT4<platform::float16> {
+ public:
+  using Type = int2;
 };
 
+// Vectorization trait 2 * sizeof(T)
+template <typename T>
+class VecT2 {};
 template <>
-union vec_t<platform::float16, 4> {
-  int2 s;
-  platform::float16 v[4];
+class VecT2<double> {
+ public:
+  using Type = int4;
+};
+template <>
+class VecT2<float> {
+ public:
+  using Type = int2;
+};
+template <>
+class VecT2<platform::float16> {
+ public:
+  using Type = int;
 };
 
-template <typename T, typename VECT, int VPT, int WARP_PER_BLOCK>
-__global__ void VecSoftmaxForward(T* dst, const T* src, const int batch_size,
-                                  const int softmax_ele) {
-  int offset = blockIdx.x * softmax_ele * WARP_PER_BLOCK;
-  int idx = threadIdx.x * VPT;
-
-  VECT buf = reinterpret_cast<const VECT*>(&src[offset + idx])[0];
-  T* bufp = reinterpret_cast<T*>(&buf);
-  float4 val4;
-  float* val4p = reinterpret_cast<float*>(&val4);
-  for (int i = 0; i < VPT; ++i) {
-    val4p[i] = static_cast<float>(bufp[i]);
-  }
-  float val = val4.x + val4.y + val4.z + val4.w;
-  float max_val = math::warpReduceMax<float>(
-      max(max(val4.x, val4.y), max(val4.z, val4.w)), 0xffffffff);
-  float4 tmp4 = make_float4(__expf(val4.x - max_val), __expf(val4.y - max_val),
-                            __expf(val4.z - max_val), __expf(val4.w - max_val));
-  float* tmp4p = reinterpret_cast<float*>(&tmp4);
-  float invsum = 1.f / (math::warpReduceSum<float>(
-                            tmp4.x + tmp4.y + tmp4.z + tmp4.w, 0xffffffff) +
-                        1e-6f);
-  for (int i = 0; i < VPT; ++i) {
-    bufp[i] = static_cast<T>(tmp4p[i] * invsum);
-  }
-  reinterpret_cast<VECT*>(&dst[offset + idx])[0] = buf;
+int static inline log2_ceil(int value) {
+  int log2_value = 0;
+  while ((1 << log2_value) < value) ++log2_value;
+  return log2_value;
 }
 
-template <typename T, int WARP_BATCH, int WARP_SIZE_SOFTMAX>
-__device__ __forceinline__ void warp_reduce_sum(T* sum) {
+/*
+Core function of computing softmax forward for axis=-1.
+The computation includes
+  - Compute maximum of batch: maxvalue_{i} = max_j src_{i,j}
+  - Compute sum of exp batch: s_{i} = sum_{j}{ exp(src_{i,j} - maxvalue_{i} }
+  - Compute: (a_{i,j} - maxvalue_{i}) / s_{i}
+One warp (32 threads) is used to compute 1 or 2 batch (kBatchSize).
+For reduction max (sum), firstly compute max (sum) to one warp, then use shuffle
+api to compute max (sum) in one warp.
+*/
+template <typename T, typename VecT, typename AccT, int Log2Elements,
+          bool LogMode = false>
+__global__ void WarpSoftmaxForward(T* softmax, const T* src,
+                                   const int batch_size, const int stride,
+                                   const int element_count) {
+  constexpr int kDimCeil = 1 << Log2Elements;
+  constexpr int kWarpSize = (kDimCeil < 32) ? kDimCeil : 32;
+  constexpr int kVSize = sizeof(VecT) / sizeof(T);
+  constexpr int kIterations = kDimCeil / kWarpSize;
+  constexpr int kIterationsV =
+      (kIterations >= kVSize) ? (kIterations / kVSize) : 1;
+  constexpr int kBatchSize = (kDimCeil <= 32) ? 2 : 1;
+
+  int first_batch = (blockDim.y * blockIdx.x + threadIdx.y) * kBatchSize;
+
+  // max index to read
+  int idx_max_v[kBatchSize];
 #pragma unroll
-  for (int offset = WARP_SIZE_SOFTMAX / 2; offset > 0; offset /= 2) {
-#pragma unroll
-    for (int i = 0; i < WARP_BATCH; ++i) {
-      T sum_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
-      sum[i] = sum[i] + sum_val;
-    }
+  for (int i = 0; i < kBatchSize; i++) {
+    int idx_max = ((i + first_batch) < batch_size) ? element_count : 0;
+    idx_max_v[i] = idx_max / kVSize;
   }
-}
 
-template <typename T, int WARP_BATCH, int WARP_SIZE_SOFTMAX>
-__device__ __forceinline__ void warp_reduce_max(T* sum) {
+  // read data from global memory
+  AccT srcdata[kBatchSize][kIterationsV][kVSize];
+
+#pragma unroll
+  for (int i = 0; i < kBatchSize; ++i) {
+// read data
+#pragma unroll
+    for (int it = 0; it < kIterationsV; ++it) {
+      int src_idx = threadIdx.x + it * kWarpSize;
+      if (kVSize == 1) {
+        if (src_idx < idx_max_v[i]) {
+          srcdata[i][it][0] =
+              static_cast<AccT>(src[(first_batch + i) * stride + src_idx]);
+        } else {
+          srcdata[i][it][0] = -std::numeric_limits<AccT>::infinity();
+        }
+      } else {
+        const VecT* src_v =
+            reinterpret_cast<const VecT*>(&src[(first_batch + i) * stride]);
+        if (src_idx < idx_max_v[i]) {
+          VecT srctmp = src_v[src_idx];
+          const T* srcinptr = reinterpret_cast<const T*>(&srctmp);
 #pragma unroll
-  for (int offset = WARP_SIZE_SOFTMAX / 2; offset > 0; offset /= 2) {
+          for (int s = 0; s < kVSize; s++) {
+            srcdata[i][it][s] = static_cast<AccT>(srcinptr[s]);
+          }
+        } else {
 #pragma unroll
-    for (int i = 0; i < WARP_BATCH; ++i) {
-      T max_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
-      sum[i] = max(sum[i], max_val);
+          for (int s = 0; s < kVSize; s++) {
+            srcdata[i][it][s] = -std::numeric_limits<AccT>::infinity();
+          }
+        }
+      }
     }
   }
-}
-
-template <typename T, typename AccT, int Log2Elements>
-__global__ void WarpSoftmaxForward(T* dst, const T* src, const int batch_size,
-                                   const int stride, const int element_count) {
-  constexpr int next_power_of_two = 1 << Log2Elements;
-  constexpr int warp_size_softmax =
-      (next_power_of_two < 32) ? next_power_of_two : 32;
-  constexpr int WARP_ITERATIONS = next_power_of_two / warp_size_softmax;
-  constexpr int WARP_BATCH = (next_power_of_two <= 128) ? 2 : 1;
 
-  int first_batch = (blockDim.y * blockIdx.x + threadIdx.y) * WARP_BATCH;
-
-  int local_batches = batch_size - first_batch;
-  if (local_batches > WARP_BATCH) {
-    local_batches = WARP_BATCH;
-  }
-
-  int local_idx = threadIdx.x;
-
-  src += first_batch * stride + local_idx;
-  dst += first_batch * stride + local_idx;
+  // compute max value
+  AccT max_value[kBatchSize];
+#pragma unroll
+  for (int i = 0; i < kBatchSize; ++i) {
+    // it = 0
+    AccT valmax = srcdata[i][0][0];
+#pragma unroll
+    for (int s = 1; s < kVSize; ++s) {
+      valmax = (valmax > srcdata[i][0][s]) ? valmax : srcdata[i][0][s];
+    }
+    max_value[i] = valmax;
 
-  // load data from global memory
-  AccT elements[WARP_BATCH][WARP_ITERATIONS];
-  for (int i = 0; i < WARP_BATCH; ++i) {
-    int batch_element_count = (i >= local_batches) ? 0 : element_count;
-    for (int it = 0; it < WARP_ITERATIONS; ++it) {
-      int element_index = local_idx + it * warp_size_softmax;
-      if (element_index < batch_element_count) {
-        elements[i][it] =
-            static_cast<float>(src[i * element_count + it * warp_size_softmax]);
-      } else {
-        elements[i][it] = -std::numeric_limits<AccT>::infinity();
+// it = 1, 2, ...
+#pragma unroll
+    for (int it = 1; it < kIterationsV; ++it) {
+      AccT valmax = srcdata[i][it][0];
+#pragma unroll
+      for (int s = 1; s < kVSize; ++s) {
+        valmax = (valmax > srcdata[i][it][s]) ? valmax : srcdata[i][it][s];
       }
+      max_value[i] = (max_value[i] > valmax) ? max_value[i] : valmax;
     }
   }
+  WarpReduceMax<AccT, kBatchSize, kWarpSize>(max_value);
 
-  // compute max_value
-  AccT max_value[WARP_BATCH];
+  // compute sum
+  AccT sum[kBatchSize];
 #pragma unroll
-  for (int i = 0; i < WARP_BATCH; ++i) {
-    max_value[i] = elements[i][0];
+  for (int i = 0; i < kBatchSize; ++i) {
+    // it = 0
+    if (LogMode) {
+      sum[i] = std::exp(srcdata[i][0][0] - max_value[i]);
+    } else {
+      srcdata[i][0][0] = std::exp(srcdata[i][0][0] - max_value[i]);
+      sum[i] = srcdata[i][0][0];
+    }
 #pragma unroll
-    for (int it = 1; it < WARP_ITERATIONS; ++it) {
-      max_value[i] =
-          (max_value[i] > elements[i][it]) ? max_value[i] : elements[i][it];
+    for (int s = 1; s < kVSize; ++s) {
+      if (LogMode) {
+        sum[i] += std::exp(srcdata[i][0][s] - max_value[i]);
+      } else {
+        srcdata[i][0][s] = std::exp(srcdata[i][0][s] - max_value[i]);
+        sum[i] += srcdata[i][0][s];
+      }
     }
-  }
-  warp_reduce_max<AccT, WARP_BATCH, warp_size_softmax>(max_value);
 
-  AccT sum[WARP_BATCH]{0.0f};
+// it = 1, 2, ...
 #pragma unroll
-  for (int i = 0; i < WARP_BATCH; ++i) {
+    for (int it = 1; it < kIterationsV; ++it) {
 #pragma unroll
-    for (int it = 0; it < WARP_ITERATIONS; ++it) {
-      elements[i][it] = (std::exp((elements[i][it] - max_value[i])));
-      sum[i] += elements[i][it];
+      for (int s = 0; s < kVSize; ++s) {
+        if (LogMode) {
+          sum[i] += std::exp(srcdata[i][it][s] - max_value[i]);
+        } else {
+          srcdata[i][it][s] = std::exp(srcdata[i][it][s] - max_value[i]);
+          sum[i] += srcdata[i][it][s];
+        }
+      }
     }
   }
-  warp_reduce_sum<AccT, WARP_BATCH, warp_size_softmax>(sum);
+  WarpReduceSum<AccT, kBatchSize, kWarpSize>(sum);
 
-// store result
+// write result to global memory
 #pragma unroll
-  for (int i = 0; i < WARP_BATCH; ++i) {
-    if (i >= local_batches) break;
+  for (int i = 0; i < kBatchSize; ++i) {
+    if (LogMode) {
+      sum[i] = std::log(sum[i]);
+    }
+
 #pragma unroll
-    for (int it = 0; it < WARP_ITERATIONS; ++it) {
-      int element_index = local_idx + it * warp_size_softmax;
-      if (element_index < element_count) {
-        dst[i * element_count + it * warp_size_softmax] =
-            elements[i][it] / sum[i];
+    for (int it = 0; it < kIterationsV; ++it) {
+      int idx = threadIdx.x + it * kWarpSize;
+      if (kVSize == 1) {
+        if (idx < idx_max_v[i]) {
+          if (LogMode) {
+            softmax[(first_batch + i) * stride + idx] =
+                srcdata[i][it][0] - max_value[i] - sum[i];
+          } else {
+            softmax[(first_batch + i) * stride + idx] =
+                srcdata[i][it][0] / sum[i];
+          }
+        } else {
+          break;
+        }
       } else {
-        break;
+        VecT* softmax_v =
+            reinterpret_cast<VecT*>(&softmax[(first_batch + i) * stride]);
+        VecT tmpdata;
+        T* tmpptr = reinterpret_cast<T*>(&tmpdata);
+#pragma unroll
+        for (int s = 0; s < kVSize; ++s) {
+          if (LogMode) {
+            tmpptr[s] = srcdata[i][it][s] - max_value[i] - sum[i];
+          } else {
+            tmpptr[s] = srcdata[i][it][s] / sum[i];
+          }
+        }
+
+        if (idx < idx_max_v[i]) {
+          softmax_v[idx] = tmpdata;
+        } else {
+          break;
+        }
       }
     }
   }
 }
 
-template <typename T, typename AccT, int Log2Elements>
-__global__ void softmax_warp_backward(T* gradInput, const T* grad,
-                                      const T* output, int batch_size,
-                                      int stride, int element_count) {
-  constexpr int next_power_of_two = 1 << Log2Elements;
-  constexpr int warp_size_softmax =
-      (next_power_of_two < 32) ? next_power_of_two : 32;
-  constexpr int WARP_ITERATIONS = next_power_of_two / warp_size_softmax;
-  constexpr int WARP_BATCH = (next_power_of_two <= 128) ? 2 : 1;
-
-  int first_batch = (blockDim.y * blockIdx.x + threadIdx.y) * WARP_BATCH;
-
+/*
+Core function of computing softmax backward for axis=-1.
+The computation includes
+  - Compute sum of exp batch: s_{i} = sum_{j} {src_{i,j} * grad_{i,j}
+  - Compute src_{i,j} * ( grad_{i,j}) - s_{i} )
+One warp (32 threads) is used to compute 1 or 2 batch (kBatchSize).
+For reduction max (sum), firstly compute max (sum) to one warp, then use shuffle
+api to compute max (sum) in one warp.
+*/
+template <typename T, typename VecT, typename AccT, int Log2Elements,
+          bool LogMode = false>
+__global__ void WarpSoftmaxBackward(T* dst, const T* grad, const T* src,
+                                    int batch_size, int stride,
+                                    int element_count) {
+  constexpr int kVSize = sizeof(VecT) / sizeof(T);
+  constexpr int kDimCeil = 1 << Log2Elements;
+  constexpr int kWarpSize = (kDimCeil < 32) ? kDimCeil : 32;
+  constexpr int kIterations = kDimCeil / kWarpSize;
+  constexpr int kBatchSize = (kDimCeil <= 128) ? 2 : 1;
+  constexpr int kIterationsV =
+      (kIterations >= kVSize) ? (kIterations / kVSize) : 1;
+  int element_count_v = element_count / kVSize;
+
+  int first_batch = (blockDim.y * blockIdx.x + threadIdx.y) * kBatchSize;
   int local_batches = batch_size - first_batch;
-  if (local_batches > WARP_BATCH) {
-    local_batches = WARP_BATCH;
+  if (local_batches > kBatchSize) {
+    local_batches = kBatchSize;
   }
 
-  int local_idx = threadIdx.x % warp_size_softmax;
-
-  int thread_offset = first_batch * stride + local_idx;
-  grad += thread_offset;
-  output += thread_offset;
-  gradInput += thread_offset;
-
-  // load data from global memory
-  AccT grad_reg[WARP_BATCH][WARP_ITERATIONS];
-  AccT output_reg[WARP_BATCH][WARP_ITERATIONS];
-  for (int i = 0; i < WARP_BATCH; ++i) {
-    int batch_element_count = (i >= local_batches) ? 0 : element_count;
-    for (int it = 0; it < WARP_ITERATIONS; ++it) {
-      int element_index = local_idx + it * warp_size_softmax;
-      if (element_index < batch_element_count) {
-        grad_reg[i][it] =
-            static_cast<AccT>(grad[i * element_count + it * warp_size_softmax]);
-        output_reg[i][it] = static_cast<AccT>(
-            output[i * element_count + it * warp_size_softmax]);
+  // read data from global memory
+  VecT src_reg[kBatchSize][kIterationsV];
+  VecT grad_reg[kBatchSize][kIterationsV];
+
+  for (int i = 0; i < kBatchSize; ++i) {
+    const VecT* src_v =
+        reinterpret_cast<const VecT*>(&src[(first_batch + i) * stride]);
+    const VecT* grad_v =
+        reinterpret_cast<const VecT*>(&grad[(first_batch + i) * stride]);
+
+    // max index to read
+    int idx_max = (i < local_batches) ? element_count : 0;
+    int idx_max_v = idx_max / kVSize;
+
+    // read data
+    for (int it = 0; it < kIterationsV; ++it) {
+      int src_idx = threadIdx.x + it * kWarpSize;
+      if (src_idx < idx_max_v) {
+        src_reg[i][it] = src_v[src_idx];
+        grad_reg[i][it] = grad_v[src_idx];
       } else {
-        grad_reg[i][it] = AccT(0);
-        output_reg[i][it] = AccT(0);
+#pragma unroll
+        for (int s = 0; s < kVSize; s++) {
+          reinterpret_cast<T*>(&src_reg[i][it])[s] = 0.0;
+          reinterpret_cast<T*>(&grad_reg[i][it])[s] = 0.0;
+        }
       }
     }
   }
 
-  AccT sum[WARP_BATCH];
+  // compute sum
+  AccT sum[kBatchSize]{0.0};
+#pragma unroll
+  for (int i = 0; i < kBatchSize; ++i) {
 #pragma unroll
-  for (int i = 0; i < WARP_BATCH; ++i) {
-    sum[i] = grad_reg[i][0];
+    for (int it = 0; it < kIterationsV; ++it) {
+      T* gradptr = reinterpret_cast<T*>(&grad_reg[i][it]);
+      T* srcptr = reinterpret_cast<T*>(&src_reg[i][it]);
 #pragma unroll
-    for (int it = 1; it < WARP_ITERATIONS; ++it) {
-      sum[i] += grad_reg[i][it];
+      for (int s = 0; s < kVSize; ++s) {
+        if (LogMode) {
+          sum[i] += static_cast<AccT>(gradptr[s]);
+        } else {
+          sum[i] += static_cast<AccT>(gradptr[s] * srcptr[s]);
+        }
+      }
     }
   }
-  warp_reduce_sum<AccT, WARP_BATCH, warp_size_softmax>(sum);
+  WarpReduceSum<AccT, kBatchSize, kWarpSize>(sum);
 
-// store result
+// write result
 #pragma unroll
-  for (int i = 0; i < WARP_BATCH; ++i) {
+  for (int i = 0; i < kBatchSize; ++i) {
     if (i >= local_batches) break;
+
+    VecT* dst_v = reinterpret_cast<VecT*>(&dst[(first_batch + i) * stride]);
+
+    // max index to write
+    int idx_max = (i < local_batches) ? element_count : 0;
+    int idx_max_v = idx_max / kVSize;
+
 #pragma unroll
-    for (int it = 0; it < WARP_ITERATIONS; ++it) {
-      int element_index = local_idx + it * warp_size_softmax;
-      if (element_index < element_count) {
-        // compute gradients
-        gradInput[i * element_count + it * warp_size_softmax] =
-            (grad_reg[i][it] - output_reg[i][it] * sum[i]);
+    for (int it = 0; it < kIterationsV; ++it) {
+      VecT tmpdata;
+      T* tmpptr = reinterpret_cast<T*>(&tmpdata);
+      T* gradptr = reinterpret_cast<T*>(&grad_reg[i][it]);
+      T* srcptr = reinterpret_cast<T*>(&src_reg[i][it]);
+#pragma unroll
+      for (int s = 0; s < kVSize; ++s) {
+        if (LogMode) {
+          tmpptr[s] = static_cast<AccT>(gradptr[s]) -
+                      std::exp(static_cast<AccT>(srcptr[s])) * sum[i];
+        } else {
+          tmpptr[s] = static_cast<AccT>(srcptr[s]) *
+                      (static_cast<AccT>(gradptr[s]) - sum[i]);
+        }
+      }
+
+      int idx = threadIdx.x + it * kWarpSize;
+      if (idx < idx_max_v) {
+        dst_v[idx] = tmpdata;
       }
     }
   }
 }
 
-template <typename T>
-__global__ void MultiplyCUDAKernel(T* C, const T* A, const T* B, int N) {
-  CUDA_KERNEL_LOOP(i, N) {
-    C[i] = static_cast<T>(static_cast<float>(A[i]) * static_cast<float>(B[i]));
+#define SOFTMAX_WARP_FORWARD_CASE(Log2Elements, AccT)                         \
+  case Log2Elements:                                                          \
+    WarpSoftmaxForward<                                                       \
+        T, VecT, AccT, Log2Elements,                                          \
+        LogMode><<<blocks, threads, 0, ctx.cuda_device_context().stream()>>>( \
+        dst, src, batch_size, stride, element_count);                         \
+    break;
+
+/*
+  Wrapper of softmax formward with template instantiation on size of input.
+*/
+template <typename T, typename VecT, bool LogMode>
+void SwitchWarpSoftmaxForward(const int blocks, const dim3 threads,
+                              const framework::ExecutionContext& ctx, T* dst,
+                              const T* src, const int batch_size,
+                              const int stride, const int element_count,
+                              int Log2Elements) {
+  using AccT = typename details::MPTypeTrait<T>::Type;
+  switch (Log2Elements) {
+    SOFTMAX_WARP_FORWARD_CASE(0, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(1, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(2, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(3, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(4, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(5, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(6, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(7, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(8, AccT);
+    SOFTMAX_WARP_FORWARD_CASE(9, AccT);
+    default:
+      break;
   }
 }
 
-template <typename T, int VPT, int WARP_PER_BLOCK>
-__global__ void VecSoftmaxBackward(T* dst, const T* grad, const T* src,
-                                   const int batch_size,
-                                   const int softmax_ele) {
-  const int offset =
-      blockIdx.x * softmax_ele * WARP_PER_BLOCK + threadIdx.x * VPT;
-
-  float local_sum_gy = 0.f;
-  vec_t<T, VPT> local_grad;
-  vec_t<T, VPT> local_src;
-
-  local_grad.s =
-      reinterpret_cast<const decltype(local_grad.s)*>(&grad[offset])[0];
-  local_src.s = reinterpret_cast<const decltype(local_src.s)*>(&src[offset])[0];
-
-  for (int i = 0; i < VPT; ++i) {
-    local_sum_gy += static_cast<float>(local_grad.v[i]) *
-                    static_cast<float>(local_src.v[i]);
-  }
-  float sum_gy = math::warpReduceSum<float>(local_sum_gy, 0xffffffff);
+#define SOFTMAX_WARP_BACKWARD_CASE(Log2Elements, AccT)                        \
+  case Log2Elements:                                                          \
+    WarpSoftmaxBackward<                                                      \
+        T, VecT, AccT, Log2Elements,                                          \
+        LogMode><<<blocks, threads, 0, ctx.cuda_device_context().stream()>>>( \
+        dst, grad, src, batch_size, stride, element_count);                   \
+    break;
 
-  vec_t<T, VPT> local_dst;
-  for (int i = 0; i < VPT; ++i) {
-    local_dst.v[i] =
-        static_cast<T>(static_cast<float>(local_src.v[i]) *
-                       (static_cast<float>(local_grad.v[i]) - sum_gy));
+/*
+Wrapper of softmax backward with template instantiation on size of input.
+*/
+template <typename T, typename VecT, bool LogMode>
+void SwitchWarpSoftmaxBackward(const int blocks, const dim3 threads,
+                               const framework::ExecutionContext& ctx, T* dst,
+                               const T* grad, const T* src,
+                               const int batch_size, const int stride,
+                               const int element_count, int Log2Elements) {
+  using AccT = typename details::MPTypeTrait<T>::Type;
+  switch (Log2Elements) {
+    SOFTMAX_WARP_BACKWARD_CASE(0, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(1, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(2, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(3, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(4, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(5, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(6, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(7, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(8, AccT);
+    SOFTMAX_WARP_BACKWARD_CASE(9, AccT);
+    default:
+      break;
   }
-  reinterpret_cast<decltype(local_dst.s)*>(&dst[offset])[0] = local_dst.s;
 }
 
-template <typename T>
+#undef SOFTMAX_WARP_FORWARD_CASE
+#undef SOFTMAX_WARP_BACKWARD_CASE
+
+template <typename T, bool LogMode = false>
 class SoftmaxCUDNNKernel : public framework::OpKernel<T> {
  public:
   void Compute(const framework::ExecutionContext& ctx) const override {
@@ -335,60 +462,39 @@ class SoftmaxCUDNNKernel : public framework::OpKernel<T> {
     const int D = SizeOutAxis(axis, dims);
 
     constexpr int max_dim = 320;
-    bool optimize = false;
     constexpr int warps_per_block = 4;
+
     if (D == 1 && dim <= max_dim && sizeof(T) <= 4) {
-      if (dim == 128 && N % warps_per_block == 0) {
-        optimize = true;
-        // a warp for a batch, 4 elements for a thread, only support the softmax
-        // dim size = 128 currently
-        if (sizeof(T) == 2) {
-          VecSoftmaxForward<T, int2, 4, warps_per_block><<<
-              N / warps_per_block, warps_per_block * WARP_SIZE, 0,
-              ctx.cuda_device_context().stream()>>>(out_data, x->data<T>(), N,
-                                                    dim);
-        } else if (sizeof(T) == 4) {
-          VecSoftmaxForward<T, int4, 4, warps_per_block><<<
-              N / warps_per_block, warps_per_block * WARP_SIZE, 0,
-              ctx.cuda_device_context().stream()>>>(out_data, x->data<T>(), N,
-                                                    dim);
-        } else {
-          assert(false && "not support");
-        }
-      } else if (dim < max_dim) {
-        optimize = true;
-        int log2_elements = static_cast<int>(log2_ceil(dim));
-        const int next_power_of_two = 1 << log2_elements;
-
-        int warp_size = (next_power_of_two < 32) ? next_power_of_two : 32;
-
-        int batches_per_warp = (next_power_of_two <= 128) ? 2 : 1;
-
-        // use 128 threads per block to maximimize gpu utilization
-        constexpr int threads_per_block = 128;
-
-        int warps_per_block = (threads_per_block / warp_size);
-        int batches_per_block = warps_per_block * batches_per_warp;
-        int blocks = (N + batches_per_block - 1) / batches_per_block;
-        dim3 threads(warp_size, warps_per_block, 1);
-
-        switch (log2_elements) {
-          LAUNCH_SOFTMAX_WARP_FORWARD(0);  // 1
-          LAUNCH_SOFTMAX_WARP_FORWARD(1);  // 2
-          LAUNCH_SOFTMAX_WARP_FORWARD(2);  // 4
-          LAUNCH_SOFTMAX_WARP_FORWARD(3);  // 8
-          LAUNCH_SOFTMAX_WARP_FORWARD(4);  // 16
-          LAUNCH_SOFTMAX_WARP_FORWARD(5);  // 32
-          LAUNCH_SOFTMAX_WARP_FORWARD(6);  // 64
-          LAUNCH_SOFTMAX_WARP_FORWARD(7);  // 128
-          LAUNCH_SOFTMAX_WARP_FORWARD(8);  // 256
-          LAUNCH_SOFTMAX_WARP_FORWARD(9);  // 512
-          default:
-            break;
-        }
+      const int kDimLog2 = static_cast<int>(log2_ceil(dim));
+      const int kDimCeil = 1 << kDimLog2;
+      int kWarpSize = (kDimCeil < 32) ? kDimCeil : 32;
+      int batches_per_warp = (kDimCeil <= 32) ? 2 : 1;
+
+      // use 128 threads per block to maximimize gpu utilization
+      constexpr int threads_per_block = 128;
+
+      int warps_per_block = (threads_per_block / kWarpSize);
+      int batches_per_block = warps_per_block * batches_per_warp;
+      int blocks = (N + batches_per_block - 1) / batches_per_block;
+      dim3 threads(kWarpSize, warps_per_block, 1);
+
+      // vectorization read/write
+      using T4 = typename VecT4<T>::Type;
+      using T2 = typename VecT2<T>::Type;
+      if (dim % 4 == 0) {
+        SwitchWarpSoftmaxForward<T, T4, LogMode>(blocks, threads, ctx, out_data,
+                                                 x->data<T>(), N, dim, dim,
+                                                 kDimLog2);
+      } else if (dim % 2 == 0) {
+        SwitchWarpSoftmaxForward<T, T2, LogMode>(blocks, threads, ctx, out_data,
+                                                 x->data<T>(), N, dim, dim,
+                                                 kDimLog2);
+      } else {
+        SwitchWarpSoftmaxForward<T, T, LogMode>(blocks, threads, ctx, out_data,
+                                                x->data<T>(), N, dim, dim,
+                                                kDimLog2);
       }
-    }
-    if (!optimize) {
+    } else {
       ScopedTensorDescriptor desc;
       std::vector<int> tensor_dims = {N, dim, D, 1};
       DataLayout layout = DataLayout::kNCHW;
@@ -405,22 +511,37 @@ class SoftmaxCUDNNKernel : public framework::OpKernel<T> {
 #ifdef PADDLE_WITH_HIP
       auto mode = axis == rank - 1 ? MIOPEN_SOFTMAX_MODE_INSTANCE
                                    : MIOPEN_SOFTMAX_MODE_CHANNEL;
-      PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxForward(
-          handle, platform::CudnnDataType<T>::kOne(), desc_, x->data<T>(),
-          platform::CudnnDataType<T>::kZero(), desc_, out_data));
+      if (LogMode) {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxForward_V2(
+            handle, platform::CudnnDataType<T>::kOne(), desc_, x->data<T>(),
+            platform::CudnnDataType<T>::kZero(), desc_, out_data,
+            MIOPEN_SOFTMAX_LOG, mode));
+      } else {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxForward_V2(
+            handle, platform::CudnnDataType<T>::kOne(), desc_, x->data<T>(),
+            platform::CudnnDataType<T>::kZero(), desc_, out_data,
+            MIOPEN_SOFTMAX_ACCURATE, mode));
+      }
 #else
       auto mode = axis == rank - 1 ? CUDNN_SOFTMAX_MODE_INSTANCE
                                    : CUDNN_SOFTMAX_MODE_CHANNEL;
-      PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxForward(
-          handle, CUDNN_SOFTMAX_ACCURATE, mode,
-          platform::CudnnDataType<T>::kOne(), desc_, x->data<T>(),
-          platform::CudnnDataType<T>::kZero(), desc_, out_data));
+      if (LogMode) {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxForward(
+            handle, CUDNN_SOFTMAX_LOG, mode, platform::CudnnDataType<T>::kOne(),
+            desc_, x->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
+            out_data));
+      } else {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxForward(
+            handle, CUDNN_SOFTMAX_ACCURATE, mode,
+            platform::CudnnDataType<T>::kOne(), desc_, x->data<T>(),
+            platform::CudnnDataType<T>::kZero(), desc_, out_data));
+      }
 #endif
     }
   }
 };
 
-template <typename T>
+template <typename T, bool LogMode = false>
 class SoftmaxGradCUDNNKernel : public framework::OpKernel<T> {
  public:
   void Compute(const framework::ExecutionContext& ctx) const override {
@@ -437,78 +558,38 @@ class SoftmaxGradCUDNNKernel : public framework::OpKernel<T> {
     const int N = SizeToAxis(axis, dims);
     const int D = SizeOutAxis(axis, dims);
 
+    constexpr int max_dim = 320;
     constexpr int warps_per_block = 4;
-    constexpr bool warp_softmax_available =
-        std::is_same<T, float>::value ||
-        std::is_same<T, platform::float16>::value;
-    bool optimize = false;
-    if (D == 1 && warp_softmax_available) {
-      if (dim == 128 && N % warps_per_block == 0) {
-        optimize = true;
-        if (std::is_same<T, float>::value) {
-          VecSoftmaxBackward<float, 4, warps_per_block><<<
-              N / warps_per_block, warps_per_block * WARP_SIZE, 0,
-              ctx.cuda_device_context().stream()>>>(dx->data<float>(),
-                                                    dout->data<float>(),
-                                                    out->data<float>(), N, dim);
-        } else if (std::is_same<T, platform::float16>::value) {
-          VecSoftmaxBackward<platform::float16, 4, warps_per_block><<<
-              N / warps_per_block, warps_per_block * WARP_SIZE, 0,
-              ctx.cuda_device_context().stream()>>>(
-              dx->data<platform::float16>(), dout->data<platform::float16>(),
-              out->data<platform::float16>(), N, dim);
-        } else {
-          PADDLE_ENFORCE_EQ(
-              warp_softmax_available, true,
-              platform::errors::Unimplemented(
-                  "Warp softmax backward is only available for fp32 and fp16"));
-        }
-      } else if (dim < 40 && dim % 32 != 0) {
-        optimize = true;
-        Tensor mul_grad;
-        int numel = N * dim;
-        mul_grad.mutable_data<T>({numel}, ctx.GetPlace());
-
-        auto stream = ctx.cuda_device_context().stream();
-        auto& dev_ctx =
-            ctx.template device_context<platform::CUDADeviceContext>();
-        auto config = GetGpuLaunchConfig1D(dev_ctx, numel);
-
-        MultiplyCUDAKernel<T><<<config.block_per_grid.x,
-                                config.thread_per_block.x, 0, stream>>>(
-            mul_grad.data<T>(), dout->data<T>(), out->data<T>(), numel);
-
-        int log2_elements = log2_ceil(dim);
-        const int next_power_of_two = 1 << log2_elements;
-
-        int warp_size = (next_power_of_two < 32) ? next_power_of_two : 32;
-
-        int batches_per_warp = (next_power_of_two <= 128) ? 2 : 1;
-
-        constexpr int threads_per_block = 128;
-
-        int warps_per_block = (threads_per_block / warp_size);
-        int batches_per_block = warps_per_block * batches_per_warp;
-        int blocks = (N + batches_per_block - 1) / batches_per_block;
-        dim3 threads(warp_size, warps_per_block, 1);
-
-        switch (log2_elements) {
-          LAUNCH_SOFTMAX_WARP_BACKWARD(0);  // 1
-          LAUNCH_SOFTMAX_WARP_BACKWARD(1);  // 2
-          LAUNCH_SOFTMAX_WARP_BACKWARD(2);  // 4
-          LAUNCH_SOFTMAX_WARP_BACKWARD(3);  // 8
-          LAUNCH_SOFTMAX_WARP_BACKWARD(4);  // 16
-          LAUNCH_SOFTMAX_WARP_BACKWARD(5);  // 32
-          LAUNCH_SOFTMAX_WARP_BACKWARD(6);  // 64
-          LAUNCH_SOFTMAX_WARP_BACKWARD(7);  // 128
-          LAUNCH_SOFTMAX_WARP_BACKWARD(8);  // 256
-          LAUNCH_SOFTMAX_WARP_BACKWARD(9);  // 512
-          default:
-            break;
-        }
+
+    if (D == 1 && dim <= max_dim && sizeof(T) <= 4) {
+      const int kDimLog2 = log2_ceil(dim);
+      const int kDimCeil = 1 << kDimLog2;
+      int kWarpSize = (kDimCeil < 32) ? kDimCeil : 32;
+      int batches_per_warp = (kDimCeil <= 128) ? 2 : 1;
+      constexpr int threads_per_block = 128;
+
+      int warps_per_block = (threads_per_block / kWarpSize);
+      int batches_per_block = warps_per_block * batches_per_warp;
+      int blocks = (N + batches_per_block - 1) / batches_per_block;
+      dim3 threads(kWarpSize, warps_per_block, 1);
+
+      // vectorization read/write
+      using T4 = typename VecT4<T>::Type;
+      using T2 = typename VecT2<T>::Type;
+      if (dim % 4 == 0) {
+        SwitchWarpSoftmaxBackward<T, T4, LogMode>(
+            blocks, threads, ctx, dx_data, dout->data<T>(), out->data<T>(), N,
+            dim, dim, kDimLog2);
+      } else if (dim % 2 == 0) {
+        SwitchWarpSoftmaxBackward<T, T2, LogMode>(
+            blocks, threads, ctx, dx_data, dout->data<T>(), out->data<T>(), N,
+            dim, dim, kDimLog2);
+      } else {
+        SwitchWarpSoftmaxBackward<T, T, LogMode>(
+            blocks, threads, ctx, dx_data, dout->data<T>(), out->data<T>(), N,
+            dim, dim, kDimLog2);
       }
-    }
-    if (!optimize) {
+    } else {
       ScopedTensorDescriptor desc;
       std::vector<int> tensor_dims = {N, dim, D, 1};
       DataLayout layout = DataLayout::kNCHW;
@@ -525,18 +606,32 @@ class SoftmaxGradCUDNNKernel : public framework::OpKernel<T> {
 #ifdef PADDLE_WITH_HIP
       auto mode = axis == rank - 1 ? MIOPEN_SOFTMAX_MODE_INSTANCE
                                    : MIOPEN_SOFTMAX_MODE_CHANNEL;
-      PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxBackward(
-          handle, platform::CudnnDataType<T>::kOne(), desc_, out->data<T>(),
-          desc_, dout->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
-          dx_data));
+      if (LogMode) {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxBackward_V2(
+            handle, platform::CudnnDataType<T>::kOne(), desc_, out->data<T>(),
+            desc_, dout->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
+            dx_data, MIOPEN_SOFTMAX_LOG, mode));
+      } else {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::miopenSoftmaxBackward_V2(
+            handle, platform::CudnnDataType<T>::kOne(), desc_, out->data<T>(),
+            desc_, dout->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
+            dx_data, MIOPEN_SOFTMAX_ACCURATE, mode));
+      }
 #else
       auto mode = axis == rank - 1 ? CUDNN_SOFTMAX_MODE_INSTANCE
                                    : CUDNN_SOFTMAX_MODE_CHANNEL;
-      PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxBackward(
-          handle, CUDNN_SOFTMAX_ACCURATE, mode,
-          platform::CudnnDataType<T>::kOne(), desc_, out->data<T>(), desc_,
-          dout->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
-          dx_data));
+      if (LogMode) {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxBackward(
+            handle, CUDNN_SOFTMAX_LOG, mode, platform::CudnnDataType<T>::kOne(),
+            desc_, out->data<T>(), desc_, dout->data<T>(),
+            platform::CudnnDataType<T>::kZero(), desc_, dx_data));
+      } else {
+        PADDLE_ENFORCE_CUDA_SUCCESS(platform::dynload::cudnnSoftmaxBackward(
+            handle, CUDNN_SOFTMAX_ACCURATE, mode,
+            platform::CudnnDataType<T>::kOne(), desc_, out->data<T>(), desc_,
+            dout->data<T>(), platform::CudnnDataType<T>::kZero(), desc_,
+            dx_data));
+      }
 #endif
     }
   }

paddle/fluid/operators/softmax_impl.cuh

+/* Copyright (c) 2021 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/fluid/platform/cuda_device_function.h"
+
+namespace paddle {
+namespace operators {
+
+template <typename T, int BatchSize, int WarpSize>
+__device__ __forceinline__ void WarpReduceSum(T* sum) {
+#pragma unroll
+  for (int offset = WarpSize / 2; offset > 0; offset /= 2) {
+#pragma unroll
+    for (int i = 0; i < BatchSize; ++i) {
+      T sum_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
+      sum[i] = sum[i] + sum_val;
+    }
+  }
+}
+
+template <typename T, int BatchSize, int WarpSize>
+__device__ __forceinline__ void WarpReduceMax(T* sum) {
+#pragma unroll
+  for (int offset = WarpSize / 2; offset > 0; offset /= 2) {
+#pragma unroll
+    for (int i = 0; i < BatchSize; ++i) {
+      T max_val = platform::CudaShuffleXorSync(0xFFFFFFFF, sum[i], offset);
+      sum[i] = max(sum[i], max_val);
+    }
+  }
+}
+
+}  // namespace operators
+}  // namespace paddle
\ No newline at end of file

paddle/fluid/operators/softmax_op.h

@@ -45,6 +45,14 @@ static inline int SizeFromAxis(const int axis, DDim dims) {
   return size;
 }
 
+static inline int SizeOutAxis(const int axis, DDim dims) {
+  int size = 1;
+  for (int i = axis + 1; i < dims.size(); i++) {
+    size *= dims[i];
+  }
+  return size;
+}
+
 template <typename DeviceContext, typename T>
 class SoftmaxKernel : public framework::OpKernel<T> {
  public: