On 26/03/2019 20:35, Ken Moffat via blfs-dev wrote: > I originally posted most of this to lfs-dev, thinking that since > meson was in LFS there must be something there which used it. But > AFAICS everything which uses meson is in BLFS, so moving this to > here, with some updated details. > > I was galancing at phoronix this afternoon (often taken over by the > peanut gallery, or dubious measurements, but sometimes interesting). > https://www.phoronix.com/scan.php?page=news_item&px=Fedora-Mesa-Meson-Debug-Build > > AFAICS we do NOT specify buildtype on any meson packages, but on > cmake we usually specify Release builds ? > > It appears that fedora were specifying 'plain', and that left debug > assertions in the build, which slowed down some things in games > (e.g. loading levels). > > https://bugs.freedesktop.org/show_bug.cgi?id=109939#c16 > > From that, the default for *mesa* is 'debugoptimized' which seems to > be what we are using. I've now got verbose output for my test > builds (ninja -v) and the default setup does not specify -DNDEBUG. > > On the current machine's setup (not building mesademos for this, I > think I'm enabling everything in mesa, including wayland backend): > > Build by the book, with logs not in the measurement: > mesa-19.0.0 1.5 GB > DESTDIR 611 MB > > Specifying -Dbuildtype=release: > mesa-19.0.0 374 MB > DESTDIR 91 MB > > That uses -O3 (there are suggestions distros might not want to use > that), and it passes -DNDEBUG. > > On my real build at the weekend, the log was unclear about the > commands actually used (hence my need for ninja -v), but it noticed > my CFLAGS and CXXFLAGS (-O2 -march=native). > > Doing another release build, but passing those (some parts are C, > others are C++) the initial -O3 for the release is early in the > arguments, my -O2 -march=native come much later so take effect. > With that (although I probably only want to pass the march part if > doing a release build on a fast machine) I get > mesa-19.0.0 345 MB > DESTDIR 75 MB. > > Summary: for mesa, -Dbuildtype=release looks like the way to go. > > The meson docs are at https://mesonbuild.com/Running-Meson.html and > my reading of that page suggests that 'debugoptimized' is not always > the default. >
Note that for mesa -Db_ndebug=true can be used to disable assertions (the default is "if_release"). Then "-O2 -g" is still passed. You can also pass -Db_nebug=false with -Dbuildtype=release, of course... BTW, using gdb with "-O2 -g" does not work well for me (I'm not a great user of gdb, so I might miss some option there): stepping gets confused if some part of the code gets optimized out, or reordered for optimization. Note that you may have access to all the options to a specific package by first running "meson setup" in a "build" directory (note the source), then "meson configure". Pierre -- http://lists.linuxfromscratch.org/listinfo/blfs-dev FAQ: http://www.linuxfromscratch.org/blfs/faq.html Unsubscribe: See the above information page
