linux-kernel - Re: [PATCH 2/2] kallsyms: build faster by using .incbin

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Date: Thu, 22 Feb 2024 09:20:26 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Masahiro Yamada" <masahiroy@...nel.org>, "Jann Horn" <jannh@...gle.com>
Cc: "Andrew Morton" <akpm@...ux-foundation.org>,
 "Nick Desaulniers" <ndesaulniers@...gle.com>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Zhen Lei" <thunder.leizhen@...wei.com>,
 linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 2/2] kallsyms: build faster by using .incbin

On Thu, Feb 22, 2024, at 05:06, Masahiro Yamada wrote:
> On Thu, Feb 22, 2024 at 5:27 AM Jann Horn <jannh@...gle.com> wrote:
>> This change reduces the time for an incremental kernel rebuild
>> (touch fs/ioctl.c, then re-run make) from 27.7s to 24.1s (medians
>> over 16 runs each) on my machine - saving around 3.6 seconds.

Nice!

..

> This reverts bea5b74504742f1b51b815bcaf9a70bddbc49ce3
>
> Somebody might struggle with debugging again, but I am not sure.
>
> Arnd?

So far, I have not needed it again, but it's only been a year.

> If the effort were "I invented a way to do kallsyms in
> one pass instead of three", it would be so much more attractive.
>
>
> I am not so sure if this grain of the optimization is exciting,
> but I confirmed that a few seconds were saved for the defconfig.
>
> I am neutral about this.

I think the time savings are worth it, especially since this
is going to help anyone building on large machines where
the compile stage is already optimized a lot but the link
stage is limited by single-thread performance.

      Arnd