On Thursday, August 11, 2016 10:43:20 PM CEST Nicholas Piggin wrote: > On Wed, 03 Aug 2016 22:13:28 +0200 > Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > On Wednesday, August 3, 2016 2:44:29 PM CEST Segher Boessenkool wrote: > > > Hi Arnd, > > > > > > On Wed, Aug 03, 2016 at 08:52:48PM +0200, Arnd Bergmann wrote: > > > > From my first look, it seems that all of lib/*.o is now getting linked > > > > into vmlinux, while we traditionally leave out everything from lib/ > > > > that is not referenced. > > > > > > > > I also see a noticeable overhead in link time, the numbers are for > > > > a cache-hot rebuild after a successful allyesconfig build, using a > > > > 24-way Opteron@2.5Ghz, just relinking vmlinux: > > > > > > > > $ time make skj30 vmlinux # before > > > > real 2m8.092s > > > > user 3m41.008s > > > > sys 0m48.172s > > > > > > > > $ time make skj30 vmlinux # after > > > > real 4m10.189s > > > > user 5m43.804s > > > > sys 0m52.988s > > > > > > Is it better when using rcT instead of rcsT? > > > > It seems to be noticeably better for the clean rebuild case, though > > not as good as the original: > > > > real 3m34.015s > > user 5m7.104s > > sys 0m49.172s > > > > I've also tried now with my own patch applied as well (linking > > each drivers/*/built-in.o into vmlinux rather than having them > > linked into drivers/built-in.o first), but that makes no > > difference. > > I just want to come back to this, because I've subbmitted the thin > archives kbuild patch, I wanted to make sure we're doing okay on > ARM/ARM64. I cross compiled with my laptop. > > For ARM64 allyesconfig: > > After building then removing all built-in.o then rebuilding vmlinux: > inclink > time make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -j8 vmlinux > real 1m18.977s > user 2m14.512s > sys 0m29.704s > > thinarc > time make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -j8 vmlinux > real 1m18.433s > user 2m6.128s > sys 0m28.372s > > > Final ld time > inclink > real 0m4.005s > user 0m3.464s > sys 0m0.536s > > thinarc > real 0m5.841s > user 0m4.916s > sys 0m0.916s > > > Build directory size is of course much better (3953MB vs 5519MB). Ok, looks great. Some downsides and some upsides here, but overall I think this is a win. > > For ARM, defconfig > > After building then removing all built-in.o then rebuilding vmlinux: > inclink > real 0m19.593s > user 0m22.372s > sys 0m6.428s > > thinarc > real 0m18.919s > user 0m21.924s > sys 0m6.400s > > > Final ld time > inclink > real 0m0.378s > user 0m0.304s > sys 0m0.076s > > thinarc > real 0m0.894s > user 0m0.684s > sys 0m0.200s This also still seems fine. > For both cases final link gets slower with thin archives. I guess there is some > per-file overhead but I thought with --whole-archive it should not be that much > slower. Still, overall time for main ar/ld phases comes out about the same in > the end so I don't think it's too much problem. Unless ARM blows up significantly > worse with a bigger config. Unfortunately I think it does. I haven't tried your latest series yet, but I think the total time for removing built-in.o and relinking went up from around 4 minutes (already way too much) to 18 minutes for me. > Linking with thin archives takes significantly more time in bfd hash lookup code. > I haven't dug much further yet. Can you try the ARM allyesconfig with thin archives? I'll follow up with two patches: one to get ARM to link without thin archives, and one that I used to get --gc-sections to work. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
