On Thu, Jan 21, 2021 at 2:42 AM 'Diab Neiroukh' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > > 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. > > Suggested-by: Danny Lin <danny@xxxxxxxxxxx> > Signed-off-by: Diab Neiroukh <lazerl0rd@xxxxxxxxxxx> This patch was correctly sent to clang-built-linux ML, but did not get any attention. I did not evaluate anything about this patch, but this patch is just adding several flags. Please try to collect Reviewed-by, Tested-by, etc. from Clang folks if you want this merged. Just a minor comment: Typos in the Makefile changes. "beyound" -> "beyond" "perfom" -> "perform" > --- > Makefile | 16 ++++++++++++++++ > init/Kconfig | 13 +++++++++++++ > 2 files changed, 29 insertions(+) > > diff --git a/Makefile b/Makefile > index b9d3a47c57cf..00f15bde5f8b 100644 > --- a/Makefile > +++ b/Makefile > @@ -740,6 +740,22 @@ else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE > KBUILD_CFLAGS += -Os > endif > > +ifdef CONFIG_POLLY_CLANG > +KBUILD_CFLAGS += -mllvm -polly \ > + -mllvm -polly-ast-use-context \ > + -mllvm -polly-invariant-load-hoisting \ > + -mllvm -polly-opt-fusion=max \ > + -mllvm -polly-run-inliner \ > + -mllvm -polly-vectorizer=stripmine > +# Polly may optimise loops with dead paths beyound what the linker > +# can understand. This may negate the effect of the linker's DCE > +# so we tell Polly to perfom proven DCE on the loops it optimises > +# in order to preserve the overall effect of the linker's DCE. > +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION > +KBUILD_CFLAGS += -mllvm -polly-run-dce > +endif > +endif > + > # Tell gcc to never replace conditional load with a non-conditional one > KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) > KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races) > diff --git a/init/Kconfig b/init/Kconfig > index 05131b3ad0f2..266d7d03ccd1 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -177,6 +177,19 @@ config BUILD_SALT > This is mostly useful for distributions which want to ensure the > build is unique between builds. It's safe to leave the default. > > +config POLLY_CLANG > + bool "Use Clang Polly optimizations" > + depends on CC_IS_CLANG && $(cc-option,-mllvm -polly) > + depends on !COMPILE_TEST > + help > + This option enables Clang's polyhedral loop optimizer known as > + Polly. Polly is able to optimize various loops throughout the > + kernel for cache locality. This requires a Clang toolchain > + compiled with support for Polly. More information can be found > + from Polly's website: > + > + https://polly.llvm.org > + > config HAVE_KERNEL_GZIP > bool > > -- > 2.30.0 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210120174146.12287-1-lazerl0rd%40thezest.dev. -- Best Regards Masahiro Yamada
