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The row-major matrix-vector multiplication code uses a threshold to check if processing 8 rows at a time would thrash the cache. This change introduces two modifications to this logic. 1. A smaller threshold for ARM and ARM64 devices. The value of this threshold was determined empirically using a Pixel2 phone, by benchmarking a large number of matrix-vector products in the range [1..4096]x[1..4096] and measuring performance separately on small and little cores with frequency pinning. On big (out-of-order) cores, this change has little to no impact. But on the small (in-order) cores, the matrix-vector products are up to 700% faster. Especially on large matrices. The motivation for this change was some internal code at Google which was using hand-written NEON for implementing similar functionality, processing the matrix one row at a time, which exhibited substantially better performance than Eigen. With the current change, Eigen handily beats that code. 2. Make the logic for choosing number of simultaneous rows apply unifiormly to 8, 4 and 2 rows instead of just 8 rows. Since the default threshold for non-ARM devices is essentially unchanged (32000 -> 32 * 1024), this change has no impact on non-ARM performance. This was verified by running the same set of benchmarks on a Xeon desktop. |
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| bench | ||
| blas | ||
| cmake | ||
| debug | ||
| demos | ||
| doc | ||
| Eigen | ||
| failtest | ||
| lapack | ||
| scripts | ||
| test | ||
| unsupported | ||
| .hgeol | ||
| .hgignore | ||
| CMakeLists.txt | ||
| COPYING.BSD | ||
| COPYING.GPL | ||
| COPYING.LGPL | ||
| COPYING.MINPACK | ||
| COPYING.MPL2 | ||
| COPYING.README | ||
| CTestConfig.cmake | ||
| CTestCustom.cmake.in | ||
| eigen3.pc.in | ||
| INSTALL | ||
| README.md | ||
| signature_of_eigen3_matrix_library | ||
Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.
For more information go to http://eigen.tuxfamily.org/.
For pull request please only use the official repository at https://bitbucket.org/eigen/eigen.
For bug reports and feature requests go to http://eigen.tuxfamily.org/bz.