Improved the performance of inner reductions.

unsupported/Eigen/CXX11/src/Tensor/TensorReduction.h

@@ -321,9 +321,12 @@ __global__ void FullReductionKernel(R, const S, I, typename S::CoeffReturnType*)
 
 #ifdef EIGEN_HAS_CUDA_FP16
 template <typename S, typename R, typename I>
-__global__ void ReductionInitKernelHalfFloat(R, const S, I, half2*);
+__global__ void ReductionInitFullReduxKernelHalfFloat(R, const S, I, half2*);
 template <int B, int N, typename S, typename R, typename I>
 __global__ void FullReductionKernelHalfFloat(R, const S, I, half*, half2*);
+template <int NPT, typename S, typename R, typename I>
+__global__ void InnerReductionKernelHalfFloat(R, const S, I, I, half*);
+
 #endif
 
 template <int NPT, typename S, typename R, typename I>
@@ -615,13 +618,17 @@ struct TensorEvaluator<const TensorReductionOp<Op, Dims, ArgType>, Device>
 #if defined(EIGEN_USE_GPU) && defined(__CUDACC__)
   template <int B, int N, typename S, typename R, typename I> friend void internal::FullReductionKernel(R, const S, I, typename S::CoeffReturnType*);
 #ifdef EIGEN_HAS_CUDA_FP16
-  template <typename S, typename R, typename I> friend void internal::ReductionInitKernelHalfFloat(R, const S, I, half2*);
+  template <typename S, typename R, typename I> friend void internal::ReductionInitFullReduxKernelHalfFloat(R, const S, I, half2*);
   template <int B, int N, typename S, typename R, typename I> friend void internal::FullReductionKernelHalfFloat(R, const S, I, half*, half2*);
+  template <int NPT, typename S, typename R, typename I> friend void internal::InnerReductionKernelHalfFloat(R, const S, I, I, half*);
 #endif
   template <int NPT, typename S, typename R, typename I> friend void internal::InnerReductionKernel(R, const S, I, I, typename S::CoeffReturnType*);
+
   template <int NPT, typename S, typename R, typename I> friend void internal::OuterReductionKernel(R, const S, I, I, typename S::CoeffReturnType*);
 #endif
 
+  template <typename S, typename O, typename D> friend struct internal::InnerReducer;
+
   // Returns the Index in the input tensor of the first value that needs to be
   // used to compute the reduction at output index "index".
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index firstInput(Index index) const {

unsupported/Eigen/CXX11/src/Tensor/TensorReductionCuda.h

@@ -147,8 +147,9 @@ __global__ void FullReductionKernel(Reducer reducer, const Self input, Index num
 #ifdef EIGEN_HAS_CUDA_FP16
 template <typename Self,
           typename Reducer, typename Index>
-__global__ void ReductionInitKernelHalfFloat(Reducer reducer, const Self input, Index num_coeffs, half2* scratch) {
+__global__ void ReductionInitFullReduxKernelHalfFloat(Reducer reducer, const Self input, Index num_coeffs, half2* scratch) {
-  eigen_assert(threadIdx.x == 1);
+  eigen_assert(blockDim.x == 1);
+  eigen_assert(gridDim.x == 1);
   if (num_coeffs % 2 != 0) {
     half last = input.m_impl.coeff(num_coeffs-1);
     *scratch = __halves2half2(last, reducer.initialize());
@@ -157,6 +158,21 @@ __global__ void ReductionInitKernelHalfFloat(Reducer reducer, const Self input,
   }
 }
 
+template <typename Self,
+          typename Reducer, typename Index>
+__global__ void ReductionInitKernelHalfFloat(Reducer reducer, const Self input, Index num_coeffs, half* output) {
+  const Index thread_id = blockIdx.x * blockDim.x + threadIdx.x;
+  const Index num_threads = blockDim.x * gridDim.x;
+  const Index num_packets = num_coeffs / 2;
+  for (Index i = thread_id; i < num_packets; i += num_threads) {
+    ((half2*)output)[i] = reducer.template initializePacket<half2>();
+  }
+
+  if (thread_id == 0 && num_coeffs % 2 != 0) {
+    output[num_coeffs-1] = reducer.initialize();
+  }
+}
+
 template <int BlockSize, int NumPerThread, typename Self,
           typename Reducer, typename Index>
 __global__ void FullReductionKernelHalfFloat(Reducer reducer, const Self input, Index num_coeffs,
@@ -251,7 +267,7 @@ struct FullReductionLauncher {
     if (num_blocks > 1) {
       // We initialize the output and the scrathpad outside the reduction kernel when we can't be sure that there
       // won't be a race conditions between multiple thread blocks.
-      LAUNCH_CUDA_KERNEL((ReductionInitKernelHalfFloat<Self, Op, Index>),
+      LAUNCH_CUDA_KERNEL((ReductionInitFullReduxKernelHalfFloat<Self, Op, Index>),
                          1, 1, 0, device, reducer, self, num_coeffs, scratch);
     }
 
@@ -361,11 +377,11 @@ __global__ void InnerReductionKernel(Reducer reducer, const Self input, Index nu
 }
 
 #ifdef EIGEN_HAS_CUDA_FP16
-/*
+
 template <int NumPerThread, typename Self,
           typename Reducer, typename Index>
 __global__ void InnerReductionKernelHalfFloat(Reducer reducer, const Self input, Index num_coeffs_to_reduce, Index num_preserved_coeffs,
-                                              half* output, half2* scratch) {
+                                              half* output) {
   eigen_assert(blockDim.y == 1);
   eigen_assert(blockDim.z == 1);
   eigen_assert(gridDim.y == 1);
@@ -375,101 +391,105 @@ __global__ void InnerReductionKernelHalfFloat(Reducer reducer, const Self input,
   eigen_assert(NumPerThread % unroll_times == 0);
   eigen_assert(unroll_times % 2 == 0);
 
-  const Index input_col_blocks = divup<Index>(num_coeffs_to_reduce, blockDim.x * NumPerThread);
+  const Index input_col_blocks = divup<Index>(num_coeffs_to_reduce, blockDim.x * NumPerThread * 2);
-  const Index num_input_blocks = input_col_blocks * num_preserved_coeffs;
+  const Index num_input_blocks = divup<Index>(input_col_blocks * num_preserved_coeffs, 2);
 
   const Index num_threads = blockDim.x * gridDim.x;
   const Index thread_id = blockIdx.x * blockDim.x + threadIdx.x;
 
   // Initialize the output values if they weren't initialized by the ReductionInitKernel
   if (gridDim.x == 1) {
-    Index i = thread_id;
+    Index i = 2*thread_id;
-    for (; i < num_preserved_coeffs; i += 2*num_threads) {
+    for (; i + 1 < num_preserved_coeffs; i += 2*num_threads) {
-      ((half2*)output)[i] = reducer.initializePacket();
+      half* loc = output + i;
+      *((half2*)loc) = reducer.template initializePacket<half2>();
     }
-    if (i + 1 < num_preserved_coeffs) {
+    if (i < num_preserved_coeffs) {
       output[i] = reducer.initialize();
     }
     __syncthreads();
   }
 
   for (Index i = blockIdx.x; i < num_input_blocks; i += gridDim.x) {
-    const Index row = i / input_col_blocks;
+    const Index row = 2 * (i / input_col_blocks);
 
     if (row + 1 < num_preserved_coeffs) {
       const Index col_block = i % input_col_blocks;
-      const Index col_begin = col_block * blockDim.x * NumPerThread + threadIdx.x;
+      const Index col_begin = 2 * (col_block * blockDim.x * NumPerThread + threadIdx.x);
 
-      half2 reduced_val1 = reducer.initializePacket();
+      half2 reduced_val1 = reducer.template initializePacket<half2>();
-      half2 reduced_val2 = reducer.initializePacket();
+      half2 reduced_val2 = reducer.template initializePacket<half2>();
 
       for (Index j = 0; j < NumPerThread; j += unroll_times) {
-        const Index last_col = col_begin + blockDim.x * (j + unroll_times - 1);
+        const Index last_col = col_begin + blockDim.x * (j + unroll_times - 1) * 2;
         if (last_col >= num_coeffs_to_reduce) {
           Index col = col_begin + blockDim.x * j;
           for (; col + 1 < num_coeffs_to_reduce; col += blockDim.x) {
-            const half2 val = input.m_impl.packet(row * num_coeffs_to_reduce + col);
+            const half2 val1 = input.m_impl.template packet<Unaligned>(row * num_coeffs_to_reduce + col);
-            reducer.reduce(val, &reduced_val);
+            reducer.reducePacket(val1, &reduced_val1);
-            // do the same for reduce val2 here
+            const half2 val2 = input.m_impl.template packet<Unaligned>((row+1) * num_coeffs_to_reduce + col);
+            reducer.reducePacket(val2, &reduced_val2);
           }
           if (col < num_coeffs_to_reduce) {
             // Peel;
-            const half last = input.m_impl.coeff(row * num_coeffs_to_reduce + col+1);
+            const half last1 = input.m_impl.coeff(row * num_coeffs_to_reduce + col);
-            const half2 val = __halves2half2(last, reducer.initialize());
+            const half2 val1 = __halves2half2(last1, reducer.initialize());
-            reducer.reducePacket(val, &reduced_val);
+            reducer.reducePacket(val1, &reduced_val1);
+            const half last2 = input.m_impl.coeff((row+1) * num_coeffs_to_reduce + col);
+            const half2 val2 = __halves2half2(last2, reducer.initialize());
+            reducer.reducePacket(val2, &reduced_val2);
           }
           break;
         } else {
           // Faster version of the loop with no branches after unrolling.
 #pragma unroll
           for (int k = 0; k < unroll_times; ++k) {
-            const Index col = col_begin + blockDim.x * (j + k);
+            const Index col = col_begin + blockDim.x * (j + k) * 2;
-            reducer.reduce(input.m_impl.packet(row * num_coeffs_to_reduce + col), &reduced_val);
+            reducer.reducePacket(input.m_impl.template packet<Unaligned>(row * num_coeffs_to_reduce + col), &reduced_val1);
+            reducer.reducePacket(input.m_impl.template packet<Unaligned>((row + 1)* num_coeffs_to_reduce + col), &reduced_val2);
           }
         }
       }
 
 #pragma unroll
       for (int offset = warpSize/2; offset > 0; offset /= 2) {
-        reducer.reducePacket(__shfl_down(reduced_val, offset, warpSize), &reduced_val);
+        reducer.reducePacket(__shfl_down(reduced_val1, offset, warpSize), &reduced_val1);
+        reducer.reducePacket(__shfl_down(reduced_val2, offset, warpSize), &reduced_val2);
       }
 
+      half val1 =  __low2half(reduced_val1);
+      reducer.reduce(__high2half(reduced_val1), &val1);
+      half val2 =  __low2half(reduced_val2);
+      reducer.reduce(__high2half(reduced_val2), &val2);
+      half2 val = __halves2half2(val1, val2);
+
       if ((threadIdx.x & (warpSize - 1)) == 0) {
-        if (row + 1 < num_preserved_coeffs) {
+        half* loc = output + row;
-          atomicReduce(&(output[row]), reduced_val, reducer);
+        atomicReduce((half2*)loc, val, reducer);
-        }
-        else {
-          atomicReduce(scratch, reduced_val, reducer);
-        }
       }
     }
   }
 }
-*/
+
 #endif
 
 template <typename Self, typename Op>
-struct InnerReducer<Self, Op, GpuDevice> {
+struct InnerReductionLauncher {
   // Unfortunately nvidia doesn't support well exotic types such as complex,
   // so reduce the scope of the optimized version of the code to the simple case
   // of floats.
   static const bool HasOptimizedImplementation = !Op::IsStateful &&
                                                  internal::is_same<typename Self::CoeffReturnType, float>::value;
 
-  template <typename Device, typename OutputType>
+  template <typename OutputType>
-  static EIGEN_DEVICE_FUNC bool run(const Self&, Op&, const Device&, OutputType*, typename Self::Index, typename Self::Index) {
+  static EIGEN_DEVICE_FUNC bool run(const Self&, Op&, const GpuDevice&, OutputType*, typename Self::Index, typename Self::Index) {
-    assert(false && "Should only be called to reduce floats on a gpu device");
+    assert(false && "Should only be called to reduce floats and half floats on a gpu device");
     return true;
   }
 
   static bool run(const Self& self, Op& reducer, const GpuDevice& device, float* output, typename Self::Index num_coeffs_to_reduce, typename Self::Index num_preserved_vals) {
     typedef typename Self::Index Index;
 
-    // It's faster to use the usual code.
-    if (num_coeffs_to_reduce <= 32) {
-      return true;
-    }
-
     const Index num_coeffs = num_coeffs_to_reduce * num_preserved_vals;
     const int block_size = 256;
     const int num_per_thread = 128;
@@ -495,9 +515,75 @@ struct InnerReducer<Self, Op, GpuDevice> {
 
     return false;
   }
+
+#ifdef EIGEN_HAS_CUDA_FP16
+  static bool run(const Self& self, Op& reducer, const GpuDevice& device, half* output, typename Self::Index num_coeffs_to_reduce, typename Self::Index num_preserved_vals) {
+    typedef typename Self::Index Index;
+
+    if (num_preserved_vals % 2 != 0) {
+      // Not supported yet, revert to the slower code path
+      std::cout << "BYPASSING OPTIMIZED CODE PATH" << std::endl;
+      return true;
+    }
+
+    const Index num_coeffs = num_coeffs_to_reduce * num_preserved_vals;
+    const int block_size = /*256*/128;
+    const int num_per_thread = /*128*/64;
+    const int dyn_blocks = divup<int>(num_coeffs, block_size * num_per_thread);
+    const int max_blocks = device.getNumCudaMultiProcessors() *
+                           device.maxCudaThreadsPerMultiProcessor() / block_size;
+    const int num_blocks = numext::mini<int>(max_blocks, dyn_blocks);
+
+    if (num_blocks > 1) {
+      // We initialize the outputs outside the reduction kernel when we can't be sure that there
+      // won't be a race conditions between multiple thread blocks.
+      const int dyn_blocks = divup<int>(num_preserved_vals, 1024);
+      const int max_blocks = device.getNumCudaMultiProcessors() *
+                           device.maxCudaThreadsPerMultiProcessor() / 1024;
+      const int num_blocks = numext::mini<int>(max_blocks, dyn_blocks);
+      LAUNCH_CUDA_KERNEL((ReductionInitKernelHalfFloat<Self, Op, Index>),
+                         1, 1, 0, device, reducer, self, num_preserved_vals, output);
+    }
+
+    LAUNCH_CUDA_KERNEL((InnerReductionKernelHalfFloat<num_per_thread, Self, Op, Index>),
+                       num_blocks, block_size, 0, device, reducer, self, num_coeffs_to_reduce, num_preserved_vals, output);
+
+    return false;
+  }
+#endif
 };
 
 
+template <typename Self, typename Op>
+struct InnerReducer<Self, Op, GpuDevice> {
+  // Unfortunately nvidia doesn't support well exotic types such as complex,
+  // so reduce the scope of the optimized version of the code to the simple case
+  // of floats and half floats.
+#ifdef EIGEN_HAS_CUDA_FP16
+  static const bool HasOptimizedImplementation = !Op::IsStateful &&
+      (internal::is_same<typename Self::CoeffReturnType, float>::value ||
+       internal::is_same<typename Self::CoeffReturnType, Eigen::half>::value);
+#else
+  static const bool HasOptimizedImplementation = !Op::IsStateful &&
+                                                 internal::is_same<typename Self::CoeffReturnType, float>::value;
+#endif
+
+  template <typename OutputType>
+  static bool run(const Self& self, Op& reducer, const GpuDevice& device, OutputType* output, typename Self::Index num_coeffs_to_reduce, typename Self::Index num_preserved_vals) {
+    assert(HasOptimizedImplementation && "Should only be called on floats or half floats");
+    const Index num_coeffs = array_prod(self.m_impl.dimensions());
+    // Don't crash when we're called with an input tensor of size 0.
+    if (num_coeffs == 0) {
+      return true;
+    }
+    // It's faster to use the usual code.
+    if (num_coeffs_to_reduce <= 128) {
+      return true;
+    }
+    return InnerReductionLauncher<Self, Op>::run(self, reducer, device, output, num_coeffs_to_reduce, num_preserved_vals);
+  }
+};
+
 template <int NumPerThread, typename Self,
           typename Reducer, typename Index>
 __global__ void OuterReductionKernel(Reducer reducer, const Self input, Index num_coeffs_to_reduce, Index num_preserved_coeffs,

unsupported/test/cxx11_tensor_of_float16_cuda.cu

@@ -249,6 +249,10 @@ void test_cuda_contractions() {
 
 
 void test_cuda_reductions(int size1, int size2, int redux) {
+
+   std::cout << "Reducing " << size1 << " by " << size2
+             << " tensor along dim " << redux << std::endl; 
+
   Eigen::CudaStreamDevice stream;
   Eigen::GpuDevice gpu_device(&stream);
   int num_elem = size1*size2;
@@ -268,8 +272,8 @@ void test_cuda_reductions(int size1, int size2, int redux) {
   Eigen::TensorMap<Eigen::Tensor<Eigen::half, 1>, Eigen::Aligned> gpu_res_float(
       d_res_float, result_size);
 
-  gpu_float1.device(gpu_device) = gpu_float1.random();
+  gpu_float1.device(gpu_device) = gpu_float1.random() - 0.5f;
-  gpu_float2.device(gpu_device) = gpu_float2.random();
+  gpu_float2.device(gpu_device) = gpu_float2.random() - 0.5f;
 
   Eigen::array<int, 1> redux_dim = {{redux}};
   gpu_res_float.device(gpu_device) = gpu_float1.sum(redux_dim).cast<Eigen::half>();
@@ -282,7 +286,6 @@ void test_cuda_reductions(int size1, int size2, int redux) {
   gpu_device.synchronize();
 
   for (int i = 0; i < result_size; ++i) {
-    std::cout << "Checking redux " << i << std::endl;
     VERIFY_IS_APPROX(full_prec(i), half_prec(i));
   }