[ Ok, this may look irrelevant to people, but I actually notice this because I do quick rebuilds *all* the time, so the 30s vs 41s difference is actually something I reacted to and then tried to figure out... ]
On Tue, May 7, 2019 at 10:59 AM Greg KH <[email protected]> wrote: > > Joel Fernandes (Google) (2): > Provide in-kernel headers to make extending kernel easier Joel and Masahiro, this commit does annoying things. It's a small thing, but it ends up grating on my kernel rebuild times, so I hope somebody can take a look at it.. Try building a kernel with no changes, and it shouldn't re-link. HOWEVER. If you re-make the config in between, the kernel/kheaders_data.tar.xz is re-generated too. I think it checks timestamps despite having that "CHK" phase that should verify just contents. I think the kernel/config_data.gz rules do the same thing, judging by the output. I use "make allmodconfig" to re-generate the same kernel config, which triggers this. The difference between "nothing changed" and "rerun 'make allmodconfig' and nothing _still_ should have changed" is quite stark: - nothing changed: rebuild in less than 30s [torvalds@i7 linux]$ time make -j32 DESCEND objtool CALL scripts/atomic/check-atomics.sh CALL scripts/checksyscalls.sh CHK include/generated/compile.h CHK kernel/kheaders_data.tar.xz Building modules, stage 2. Kernel: arch/x86/boot/bzImage is ready (#9) MODPOST 7282 modules real 0m29.379s user 1m50.586s sys 0m41.047s - do (the same) "make allmodconfig" in between, now rebuild time is just over 41s: [torvalds@i7 linux]$ make allmodconfig [torvalds@i7 linux]$ time make -j32 scripts/kconfig/conf --syncconfig Kconfig DESCEND objtool CALL scripts/atomic/check-atomics.sh CALL scripts/checksyscalls.sh CHK include/generated/compile.h GZIP kernel/config_data.gz CHK kernel/kheaders_data.tar.xz CC [M] kernel/configs.o GEN kernel/kheaders_data.tar.xz CC [M] kernel/kheaders.o Building modules, stage 2. Kernel: arch/x86/boot/bzImage is ready (#9) MODPOST 7282 modules LD [M] kernel/configs.ko LD [M] kernel/kheaders.ko real 0m41.326s user 2m17.822s sys 0m54.561s No, this isn't the end of the world, but if somebody sees a simple solution to avoid that extra ten seconds, I'd appreciate it. Linus
