Re: [PATCH v3] Makefile: support compressed debug info

From: Masahiro Yamada <masahiroy@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>,
	Fangrui Song <maskray@google.com>,
	Nick Clifton <nickc@redhat.com>,
	David Blaikie <blaikie@google.com>,
	Michal Marek <michal.lkml@markovi.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Changbin Du <changbin.du@intel.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v3] Makefile: support compressed debug info
Date: Tue, 26 May 2020 19:26:54 +0900	[thread overview]
Message-ID: <CAK7LNARtO5Pr2nxpoORSHDFWHbjP0waOmrn_TZ+rXhmYm+TORw@mail.gmail.com> (raw)
In-Reply-To: <20200521220041.87368-1-ndesaulniers@google.com>

On Fri, May 22, 2020 at 7:00 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
>
> As debug information gets larger and larger, it helps significantly save
> the size of vmlinux images to compress the information in the debug
> information sections. Note: this debug info is typically split off from
> the final compressed kernel image, which is why vmlinux is what's used
> in conjunction with GDB. Minimizing the debug info size should have no
> impact on boot times, or final compressed kernel image size.
>
> All of the debug sections will have a `C` flag set.
> $ readelf -S <object file>
>
> $ bloaty vmlinux.gcc75.compressed.dwarf4 -- \
>     vmlinux.gcc75.uncompressed.dwarf4
>
>     FILE SIZE        VM SIZE
>  --------------  --------------
>   +0.0%     +18  [ = ]       0    [Unmapped]
>  -73.3%  -114Ki  [ = ]       0    .debug_aranges
>  -76.2% -2.01Mi  [ = ]       0    .debug_frame
>  -73.6% -2.89Mi  [ = ]       0    .debug_str
>  -80.7% -4.66Mi  [ = ]       0    .debug_abbrev
>  -82.9% -4.88Mi  [ = ]       0    .debug_ranges
>  -70.5% -9.04Mi  [ = ]       0    .debug_line
>  -79.3% -10.9Mi  [ = ]       0    .debug_loc
>  -39.5% -88.6Mi  [ = ]       0    .debug_info
>  -18.2%  -123Mi  [ = ]       0    TOTAL
>
> $ bloaty vmlinux.clang11.compressed.dwarf4 -- \
>     vmlinux.clang11.uncompressed.dwarf4
>
>     FILE SIZE        VM SIZE
>  --------------  --------------
>   +0.0%     +23  [ = ]       0    [Unmapped]
>  -65.6%    -871  [ = ]       0    .debug_aranges
>  -77.4% -1.84Mi  [ = ]       0    .debug_frame
>  -82.9% -2.33Mi  [ = ]       0    .debug_abbrev
>  -73.1% -2.43Mi  [ = ]       0    .debug_str
>  -84.8% -3.07Mi  [ = ]       0    .debug_ranges
>  -65.9% -8.62Mi  [ = ]       0    .debug_line
>  -86.2% -40.0Mi  [ = ]       0    .debug_loc
>  -42.0% -64.1Mi  [ = ]       0    .debug_info
>  -22.1%  -122Mi  [ = ]       0    TOTAL
>
> For x86_64 defconfig + LLVM=1 (before):
> Elapsed (wall clock) time (h:mm:ss or m:ss): 3:22.03
> Maximum resident set size (kbytes): 43856
>
> For x86_64 defconfig + LLVM=1 (after):
> Elapsed (wall clock) time (h:mm:ss or m:ss): 3:32.52
> Maximum resident set size (kbytes): 1566776
>
> Suggested-by: David Blaikie <blaikie@google.com>
> Suggested-by: Nick Clifton <nickc@redhat.com>
> Suggested-by: Sedat Dilek <sedat.dilek@gmail.com>
> Reviewed-by: Fangrui Song <maskray@google.com>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Suggested-by seems strange to me, but
I decided to not be worried too much.

Applied to linux-kbuild.

Thanks.

-- 
Best Regards
Masahiro Yamada