compiler flags for performance

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?

|

| 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