pytorch

2e35fe95 - [te] Implement log approximation using the VML approach (#51752)

[te] Implement log approximation using the VML approach (#51752) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/51752 Using a straight power series approximation with enough terms gives precision down to the denormal range, and avoids the fp division used in the sleef approach. This is nice because recent CPUs have dual pipelined fma units, so we can compute 16 logarithms in parallel; whereas there's usually only one FP divider and it has a fairly high latency/low throughput. ghstack-source-id: 121392347 Test Plan: On my avx2+fma broadwell: ``` --------------------------------------------------------------------------- Benchmark Time CPU Iterations UserCounters... --------------------------------------------------------------------------- log_nnc_sleef/64 178 ns 178 ns 3933565 log/s=358.993M/s log_nnc_sleef/512 1286 ns 1285 ns 559459 log/s=398.354M/s log_nnc_sleef/8192 19366 ns 19364 ns 36619 log/s=423.053M/s log_nnc_sleef/32768 79288 ns 79286 ns 8718 log/s=413.287M/s log_nnc_fast/64 92 ns 92 ns 7644990 log/s=696.939M/s log_nnc_fast/512 483 ns 483 ns 1426802 log/s=1059.49M/s log_nnc_fast/8192 7519 ns 7514 ns 95319 log/s=1090.23M/s log_nnc_fast/32768 31344 ns 31338 ns 22397 log/s=1045.62M/s log_nnc_vml/64 88 ns 88 ns 7923812 log/s=728.469M/s log_nnc_vml/512 454 ns 454 ns 1521437 log/s=1.12739G/s log_nnc_vml/8192 6763 ns 6763 ns 103264 log/s=1.21136G/s log_nnc_vml/32768 26565 ns 26564 ns 23609 log/s=1.23354G/s log_aten/64 418 ns 418 ns 1651401 log/s=153.117M/s log_aten/512 801 ns 801 ns 875857 log/s=638.923M/s log_aten/8192 6877 ns 6872 ns 100840 log/s=1.19208G/s log_aten/32768 26989 ns 26988 ns 26268 log/s=1.21416G/s ``` Reviewed By: bwasti, zheng-xq Differential Revision: D26246400 fbshipit-source-id: dae47ee6baeab1a813ec4d4440748164051aed3d