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

[Simon Glass <sjg@chromium.org>]

Hi Masahiro,

On 18 February 2014 01:02, Masahiro Yamada <yamada.m@jp.panasonic.com> wrote:
> 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.

Note this is a 32-core machine.

>
>> 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.

Yes actually sandbox is pretty fast.

>
> 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.

That sounds good to me. Thanks for looking at it.

Regards,
Simon