linux-kernel - Re: [PATCH] kbuild: Disable extra debugging info in .s output

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Message-ID: <20190201151139.GK31854@zn.tnic>
Date:   Fri, 1 Feb 2019 16:11:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH] kbuild: Disable extra debugging info in .s output

On Fri, Feb 01, 2019 at 08:58:13PM +0900, Masahiro Yamada wrote:
> Variables assigned with ':=' are evaluated just on parsing Makefile.
> 
> The scripts/Makefile.build is parsed over and over again,
> so the compiler is invoked hundreds times to test these four options
> even when you are not actually building any new objects.
> 
> It is mitigated by replacing ':=' with '=',
> but they are still evaluated multiple times when generating asm-offset.

Now that you mention it, how about ?=

disable_extra_cc_dbg ?= $(call cc-option,-gno-as-locview-support)
disable_extra_cc_dbg += $(call cc-option,-fno-dwarf2-cfi-asm)
disable_extra_cc_dbg += $(call cc-option,-feliminate-unused-debug-symbols)
disable_extra_cc_dbg += $(call cc-option,-gno-statement-frontiers)

With it, the slowdown of the incremental build is ~0.2s (on an old laptop):

defconfig without:	9.6128 +- 0.0327 seconds time elapsed  ( +-  0.34% )

vs

defconfig with:		9.8483 +- 0.0273 seconds time elapsed  ( +-  0.28% )


-- 
Regards/Gruss,
    Boris.

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