linux-kernel - Re: [PATCH-next v2] arm32: enable HAVE_LD_DEAD_CODE_DATA

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Message-ID: <79b87ef0-77c4-45a9-aae2-1754f1b407fe@huawei.com>
Date: Mon, 11 Mar 2024 17:39:14 +0800
From: "liuyuntao (F)" <liuyuntao12@...wei.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
CC: Arnd Bergmann <arnd@...db.de>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Ard Biesheuvel <ardb@...nel.org>, Fangrui
 Song <maskray@...gle.com>, Russell King <linux@...linux.org.uk>, Andrew Davis
	<afd@...com>, Andrew Morton <akpm@...ux-foundation.org>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Geert Uytterhoeven
	<geert+renesas@...der.be>, Jonathan Corbet <corbet@....net>, Mike Rapoport
	<rppt@...nel.org>, Rob Herring <robh@...nel.org>, Thomas Gleixner
	<tglx@...utronix.de>, Linus Walleij <linus.walleij@...aro.org>,
	<llvm@...ts.linux.dev>
Subject: Re: [PATCH-next v2] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION



On 2024/3/11 17:14, Geert Uytterhoeven wrote:
> Hi Yuntao,
> 
> On Sat, Mar 9, 2024 at 2:24 PM liuyuntao (F) <liuyuntao12@...wei.com> wrote:
>> On 2024/3/9 16:20, Arnd Bergmann wrote:
>>> On Sat, Mar 9, 2024, at 07:14, liuyuntao (F) wrote:
>>>> On 2024/3/8 21:15, Arnd Bergmann wrote:
>>>>> On Thu, Mar 7, 2024, at 16:12, Yuntao Liu wrote:
>>>>
>>>> Thanks for the tests, CONFIG_LD_DEAD_CODE_DATA_ELIMINATION and
>>>> CONFIG_TRIM_UNUSED_KSYMS do indeed result in a significant improvement.
>>>> I found that arm32 still doesn't support CONFIG_LTO_CLANG. I've done
>>>> some work on it, but without success. I'd like to learn more about the
>>>> CONFIG_LTO_CLANG patch. Do you have any relevant links?
>>>
>>> I did not try to get it to boot and gave up when I did not see
>>> any size improvement. I think there were previous attempts to
>>> do it elsewhere, which I did not try to find.
>>>
>>
>> I tested this patch, the size improvement was only about one
>> ten-thousandth, and the compilation time had increased by about a quarter,
>> and the kernel did not boot.
>>
>> Strangely, LTO has actually increased the compilation time
>> significantly, which seems contrary to its purpose.
> 
> The purpose of LTO is to reduce code size. Doing so requires more
> processing, hence the total build time increases.
> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 

Thanks, Geert, I got it.