[GitHub] [incubator-mxnet] sxjscience commented on a change in pull request #16104: Faster Transpose 2D

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sxjscience commented on a change in pull request #16104: Faster Transpose 2D
URL: https://github.com/apache/incubator-mxnet/pull/16104#discussion_r332219914
 
 

 ##########
 File path: src/operator/tensor/matrix_op-inl.h
 ##########
 @@ -257,6 +257,42 @@ struct TransposeParam : public dmlc::Parameter<TransposeParam> {
   }
 };
 
+
+/*!
+ * \brief This function performs transpose operation on a 2D matrix by utilizing the L1 cache
+ * \param in  input tensor
+ * \param out output tensor
+ * \param row shape of dim 0 of input
+ * \param col shape of dim 1 of input
+ */
+template<typename DType>
+MSHADOW_XINLINE void Transpose2D(const DType *in, DType *out, index_t row, index_t col) {
+  // ensure cache line hits and prevent cache miss for any configuration
+  // L1 cache size to be utilized = 32kb = 2^15
+  // Largest size of a single unit of any dtype <= 8 byte = 2^3
+  // Number of elements - (2^15/2^3) = 2^12
+  // Block-size - 2^6 v 2^6 (64 v 64)
+
+  // But we could leverage unrolling of for loops (for parallelization)
+  // Block-size - 2^5 v 2^5 (32 v 32) with 4 pragma for loop unrolled
+  // blocksize * blocksize * num_threads = cache_size / dtype_size
+  index_t blocksize = 32;
+
+  for (index_t i = 0; i < row; i += blocksize) {
+    #pragma omp parallel for
+    for (index_t j = 0; j < col; j += blocksize) {
+      // transpose the block
+      #pragma unroll 4
+      for (index_t a = j; a < blocksize && a < col; ++a) {
 
 Review comment:
   Should it be  `a < j + blocksize`?

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