linux-kernel - Re: [PATCH 1/2] kbuild: remove top-level built-in.a

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Message-ID: <CAK7LNAREyw=qhRO-Cvg4O2fOnbV=zVJDE_mRZcVTkKG+B1gkRQ@mail.gmail.com>
Date:   Tue, 15 Jan 2019 18:01:34 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH 1/2] kbuild: remove top-level built-in.a

Hi Nicholas,


On Tue, Jan 15, 2019 at 5:07 PM Nicholas Piggin <npiggin@...il.com> wrote:
>
> Masahiro Yamada's on January 14, 2019 1:27 pm:
> > The symbol table in the final archive is unneeded because it is passed
> > to the linker after the --whole-archive option. Every object file in
> > the archive is included in the link anyway.
> >
> > Pass thin archives from subdirectories directly to the linker, and
> > remove the final archiving step.
>
> This seems like a good improvement. As far as I remember, it was slower
> to do the final link without the index built. Maybe I was testing it
> in a revision before moving those files into --whole-archive? If there
> is no slowdown, then I have no objection.


Thanks for the review.


I measured the performance of scripts/link-vmlinux.sh with 'perf stat'.
(20 times for each)



Before this patch:

 Performance counter stats for 'make vmlinux' (20 runs):

       5.266796537 seconds time elapsed
          ( +-  0.12% )



After this patch:

 Performance counter stats for 'make vmlinux' (20 runs):

       4.945576395 seconds time elapsed




So, the performance is slightly better.

Maybe, does omitting the 'ar' save some time?


Anyway, this commit is good.


-- 
Best Regards
Masahiro Yamada