On Wed, 12 Jul 2017 09:29:40 -0700 Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > Nicholas Piggin <npiggin@xxxxxxxxx> writes: > >> > >> I think we should aim for gc-sections to be used by default and have LTO > >> as a possible option only. > > > > I agree after it starts getting implemented and debugged by small > > system users, we could make it default in the interest of sharing > > testing and reducing combinations. > > From what i understand the main drawback in the past was > is that various linker versions become very slow with thousands of > sections. > > So it may cost you built time. For a special small build it's probably > ok, but you wouldn't want to make it default. For --gc-sections, I have found it costs almost nothing (full LTO is a different story). We will have to do more testing and get numbers before it's made default of course. > > Also usually it's only useful without modules because if you > use modules EXPORT_SYMBOL pulls in a lot of unused functions. Yes that and several other things that cause references from live code/data does reduce effectiveness. Nicolas has been working on several improvements to these (including EXPORT trimming he mentioned). > > BTW I'm still maintaining a "real LTO" patchkit here, which > has some users (mainly for binary size), but also gives some > performance. Should probably resubmit it again. The main > issue was that the old single link patch is still not forward > ported. > > https://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc.git/log/?h=lto-411-2 Yeah we should start looking at full LTO again after --gc-sections. I've been looking at your patches but actually before I saw your single link patch I did another approach. Never quite got it working exactly right, but it would be nice to avoid linking 3 extra times every build regardless of LTO! Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
