[Rd] compiler flags for performance

[arnaud gaboury]

On Fri, Jun 14, 2019 at 1:44 PM lejeczek via R-devel <r-devel using r-project.org>
wrote:

> On 13/06/2019 16:14, Dirk Eddelbuettel wrote:
> > On 13 June 2019 at 16:05, lejeczek via R-devel wrote:
> > | I'd like to ask, and I believe this place here should be best as who
> can
> > | know better, if building R with different compilers and opt flags is
> > | something worth investing time into?
>
> |
> > | Or maybe this a subject that somebody has already investigated. If yes
> > | what then are the conclusion?
>

It is worth spending sometime,but all in all, you may end  disapointed.
There are other things you may try: new Intel Linux distro (optimized for
Intelprocessors); build with Clang compiler instead of GCC; use optimized
BLAS (that's indeed a very good idea,look for openblas).

I have build R with Intel MKL.The libraries are free for one year (maybe
did it change). The build is far from being trivial. Please find on my
github[0] some details


> |
> > | Reason I ask is such that, on Centos 7.6 with different compilers from
> > | stock repo but also from so called software collections, do not
> > | render(with flags for performance) an R binaries which would perform
> any
> > | better, according to R-benchmark-25 at least, then "vanilla" packages
> > | shipped from distro.
> > |
> > | And that makes me curious - is it because R is such a case which is
> > | prone to any compiler performance optimizations?
> > |
> > | Maybe there is more structured and organized way to conduct such
> > | different-compilers-optimizations benchmarks/test?
> > |
> > | What do devel can say and advise with regards to
> compile-for-performance
> > | subject?
> >
> > Of course you do that, and add those switches to ~/.R/Makeconf.  The
> > resulting binaries may become non-portable.
> >
> > E.g. "at work" we use -march=native quite a bit but it means can't share
> > libraries from a beefier dev box with skinnier deployment boxen as they
> don't
> > have the same chipset even thought the are both x86_64 and use the same
> Linux
> > distro.
> >
> > As for which switches help in which way on different compiler: that is
> > probably best seen as a black box.  Time and profile locally, I no
> longer try
> > to generalize.   The newer 'link-time-optimizations' can help too, they
> > certainly make builds longer ...
> >
> > Dirk
> >
> I've tried the "usual" tweaks and what puzzles me is the fact, that
> -march=native and -lto(s) + Os/3 do not help much, make almost invisible
> improvements (again, judging by results from R-benchmark-25) with gcc >=
> 7 as compared to distro's package which is built with -O2 -mtune=generic
> and no ltos.
>
> Would there be other(better) way to test core R?
>
> What king of R perf increases do you guys see with compiler's opt flags,
> if any?
>
> regards, L.
>
> [0] https://github.com/gabx/R-project/tree/master/R-mkl
>
>
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