linux-kernel - Re: [GIT PULL 2/2] Kconfig updates for v5.10-rc1

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Date:   Fri, 27 Nov 2020 13:53:09 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL 2/2] Kconfig updates for v5.10-rc1

On Fri, Nov 27, 2020 at 1:15 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Oh, this is a red herring. It's "make" output being misleading, and it
> just comes from the FORCE keyword.
>
> And no, those don't actually change the end result for me.

.. and that red herring was what made me think that it always
recompiles the 'conf' binary. But no, that's not what is going on.

profiling shows that it does spend a lot of time in the compiler
(which was the other thing that made me incorrectly think it was the
conf program getting recompiled every time), but it looks like maybe
it's simply the cc-option testing that causes that:

    33.68%  cc1plus
    16.71%  cc1
    14.75%  ld
    11.36%  conf
     7.51%  sh
     7.21%  as
     3.01%  gcc
     2.44%  make
     0.58%  mkdir
     0.39%  rm
     0.33%  gcc-version.sh
     0.24%  collect2
     0.23%  cat
     0.22%  grep
     0.20%  cc-can-link.sh

Oh well, I clearly misread the problem. Maybe 1.5s is more reasonable
than I really expected it to be.

                  Linus