[U-Boot] [PATCH v8 0/38] Switch over to real Kbuild

[Masahiro Yamada]

Hello Simon,


> 
> I'm not sure whether to start a new thread or not, but here in one
> observations which might be useful.
> 
> With current master, a 'null' build (with nothing changed) takes about
> 5s for me.
> 
> time CROSS_COMPILE=/opt/linaro/gcc-linaro-arm-linux-gnueabihf-4.8-2013.08_linux/bin/arm
> -linux-gnueabihf- ARCH=arm make -j1
> real 0m4.978s
> user 0m1.144s
> sys 0m0.360s
> 
> 
> With the kbuild series, it takes a lot longer:
> 
> real 0m46.600s
> user 0m17.628s
> sys 0m8.664s

Thanks for your feedback.

Hmm, Kbuild is 9 times slower on your computer.
This is a big difference. (It was about 1.6 x slower on my box.)

I don't know where such a difference came from.

> There seem to be noticeable pauses between things happening. I'm not
> quite sure how to dig into it more. Is it possible that cc-option is
> no-longer caching the various compiler options?

I guess it's possible.

Is sandbox build slow as well?
Sandbox has no cc-option.
If cc-option is the cause of pauses, sandbox build
should be faster.

Anyway, evaluating cc-option multiple times isn't nice
and its optimization is on my TODO list.

Historically, U-Boot has included all
config.mk (arch/*/config.mk and board/*/config.mk)
every time descending into subdirectories.
That means cc-options are evaluated over and over again.
Caching cc-option is one of work arounds, but we should not
revive it.

What we should do is to include arch/*/config.mk and board/*/config.mk
only once at the top Makefile and export options.


Best Regards
Masahiro Yamada