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Polly is able to optimize various loops throughout the kernel for cache locality. A mathematical representation of the program, based on polyhedra, is analysed to find opportunistic optimisations in memory access patterns which then leads to loop transformations. Polly is not built with LLVM by default, and requires LLVM to be compiled with the Polly "project". This can be done by adding Polly to -DLLVM_ENABLE_PROJECTS, for example: -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi;polly" Preliminary benchmarking seems to show an improvement of around two percent across perf benchmarks: Benchmark | Control | Polly -------------------------------------------------------- bonnie++ -x 2 -s 4096 -r 0 | 12.610s | 12.547s perf bench futex requeue | 33.553s | 33.094s perf bench futex wake | 1.032s | 1.021s perf bench futex wake-parallel | 1.049s | 1.025s perf bench futex requeue | 1.037s | 1.020s Furthermore, Polly does not produce a much larger image size netting it to be a "free" optimisation. A comparison of a bzImage for a kernel with and without Polly is shown below: bzImage | stat --printf="%s\n" ------------------------------------- Control | 9333728 Polly | 9345792 Compile times were one percent different at best, which is well within the range of noise. Therefore, I can say with certainty that Polly has a minimal effect on compile times, if none. [Tashar02]: 1. Rework on the flag passing format. 2. Pass Polly Flags to linker as well. 3. Add `-polly-detect-keep-going` cmdline option. Change-Id: I588b3f0fedc10221383c9030c33f42d789b30fb9 Suggested-by: Danny Lin <danny@kdrag0n.dev> Signed-off-by: Diab Neiroukh <lazerl0rd@thezest.dev> Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com> Signed-off-by: Richard Raya <rdxzv.dev@gmail.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.