Hello, a small update from my side . I had (on Linux) for a couple of days our jdk11u tests + benchmarks running with -Os instead of the usual settings (-O3) . With have (independent of -Os / -O3) a bit of variance in our benchmarks ( jbb15 , jvm2008, jvm98 ) .
However the benchmark results of -Os vs. -O3 were comparable . >we discussed doing the opposite for Mac OS X recently, where builds are >currently set to -Os by default. -O3 helped various networking >(micro)benchmarks by up to 20%. What microbenchmarks do you have in mind that show much better performance with -O3 compared to -Os ? Best regards, Matthias > > Hi Martin, > > On 2019-11-27 19:03, Doerr, Martin wrote: > > Hi Claes, > > > > that kind of surprises me. I'd expect files which rather benefit from -O3 to > be far less than those which benefit from -Os. > > Most performance critical code lives inside the code cache and is not > dependent on C++ compiler optimizations. > > I'd expect GC code, C2's register allocation and a few runtime files to be > > the > most performance critical C++ code. > > So the list of files for -Os may become long. > > that might very well be the end result, and once/if we've gone down this > path long enough to see that -O3 becomes the exception, we can re- > examine the default. Changing the default and then trying to recuperate > would be hard/impossible to do incrementally. > > > > > Yeah, I think we should use native profiling information to find out what's > really going on > > > Your idea to change file by file and check for performance regression > makes sense to me, though > Hopefully we don't have to do one RFE per file.. :-) > > /Claes
