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68e79b27a5
This is a trivial rewrite of the loops that results in better prefetching and associated cache efficiency. Essentially, the problem is that modern prefetching logic is based on finite state Markov memory, a reasonable assumption that is used elsewhere in CPU's in for instance branch predictors. Surrounding loops all iterate forward through the array, making the predictor think of prefetching in the forward direction, but the intermediate loop is unnecessarily in the backward direction. Speedup is nontrivial. Benchmarks obtained by 10^6 iterations within solve_lls, with START/STOP_TIMER. File is tests/data/fate/flac-16-lpc-cholesky.err. Hardware: x86-64, Haswell, GNU/Linux. new: 17291 decicycles in solve_lls, 2096706 runs, 446 skips 17255 decicycles in solve_lls, 4193657 runs, 647 skips 17231 decicycles in solve_lls, 8384997 runs, 3611 skips 17189 decicycles in solve_lls,16771010 runs, 6206 skips 17132 decicycles in solve_lls,33544757 runs, 9675 skips 17092 decicycles in solve_lls,67092404 runs, 16460 skips 17058 decicycles in solve_lls,134188213 runs, 29515 skips old: 18009 decicycles in solve_lls, 2096665 runs, 487 skips 17805 decicycles in solve_lls, 4193320 runs, 984 skips 17779 decicycles in solve_lls, 8386855 runs, 1753 skips 18289 decicycles in solve_lls,16774280 runs, 2936 skips 18158 decicycles in solve_lls,33548104 runs, 6328 skips 18420 decicycles in solve_lls,67091793 runs, 17071 skips 18310 decicycles in solve_lls,134187219 runs, 30509 skips Reviewed-by: Michael Niedermayer <michael@niedermayer.cc> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides a mean to alter decoded Audio and Video through chain of filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements color conversion and scaling routines.
Tools
- ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
- ffplay is a minimalistic multimedia player.
- ffprobe is a simple analysis tool to inspect multimedia content.
- ffserver is a multimedia streaming server for live broadcasts.
- Additional small tools such as
aviocat,ismindexandqt-faststart.
Documentation
The offline documentation is available in the doc/ directory.
The online documentation is available in the main website and in the wiki.
Examples
Coding examples are available in the doc/examples directory.
License
FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.
Contributing
Patches should be submitted to the ffmpeg-devel mailing list using
git format-patch or git send-email. Github pull requests should be
avoided because they are not part of our review process. Few developers
follow pull requests so they will likely be ignored.