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SubjectRe: [GIT PULL] Driver core patches for 5.2-rc1
Hi Linus,


On Fri, May 10, 2019 at 5:50 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> [ 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 <gregkh@linuxfoundation.org> 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:

Yeah, I have had this in my mind for a while.

If you run "make *config" and it happens to be creating
the exactly the same .config, Kconfig should not overwrite
it at all.

If you apply the following two,
I hope you will get the behavior you like.

https://patchwork.kernel.org/patch/10938255/
https://patchwork.kernel.org/patch/10938253/

(1/2 is just a cleanup because I am touching the
same hunk.)

Because I have not sent a Kconfig pull request yet
in the current MW, I will consider to merge them.

Thanks.


> - 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



--
Best Regards
Masahiro Yamada

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