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Date: Wed, 12 Jun 2024 09:54:53 +0800
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Subject: Re: [PATCH-next v4] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
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To: Geert Uytterhoeven <geert@linux-m68k.org>
CC: <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
	<arnd@arndb.de>, <ardb@kernel.org>, <linux@armlinux.org.uk>, <afd@ti.com>,
	<akpm@linux-foundation.org>, <kirill.shutemov@linux.intel.com>,
	<corbet@lwn.net>, <rppt@kernel.org>, <robh@kernel.org>, <tglx@linutronix.de>,
	<linus.walleij@linaro.org>, <maskray@google.com>, Linux-Renesas
	<linux-renesas-soc@vger.kernel.org>, Chris Brandt <Chris.Brandt@renesas.com>
References: <20240316023932.700685-1-liuyuntao12@huawei.com>
 <CAMuHMdWMAg59p+hzeLG9Uc3X55Vt9ccNy5BRoPX0RJbxrMOFLA@mail.gmail.com>
From: "liuyuntao (F)" <liuyuntao12@huawei.com>
In-Reply-To: <CAMuHMdWMAg59p+hzeLG9Uc3X55Vt9ccNy5BRoPX0RJbxrMOFLA@mail.gmail.com>
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That's great, thanks for your testing.

On 2024/6/11 20:45, Geert Uytterhoeven wrote:
> Hi Yuntao,
> 
> On Sat, Mar 16, 2024 at 3:44 AM Yuntao Liu <liuyuntao12@huawei.com> wrote:
>> The current arm32 architecture does not yet support the
>> HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. arm32 is widely used in
>> embedded scenarios, and enabling this feature would be beneficial for
>> reducing the size of the kernel image.
>>
>> In order to make this work, we keep the necessary tables by annotating
>> them with KEEP, also it requires further changes to linker script to KEEP
>> some tables and wildcard compiler generated sections into the right place.
>> When using ld.lld for linking, KEEP is not recognized within the OVERLAY
>> command, and Ard proposed a concise method to solve this problem.
>>
>> It boots normally with defconfig, vexpress_defconfig and tinyconfig.
>>
>> The size comparison of zImage is as follows:
>> defconfig       vexpress_defconfig      tinyconfig
>> 5137712         5138024                 424192          no dce
>> 5032560         4997824                 298384          dce
>> 2.0%            2.7%                    29.7%           shrink
>>
>> When using smaller config file, there is a significant reduction in the
>> size of the zImage.
>>
>> We also tested this patch on a commercially available single-board
>> computer, and the comparison is as follows:
>> a15eb_config
>> 2161384         no dce
>> 2092240         dce
>> 3.2%            shrink
>>
>> The zImage size has been reduced by approximately 3.2%, which is 70KB on
>> 2.1M.
>>
>> Signed-off-by: Yuntao Liu <liuyuntao12@huawei.com>
>> Tested-by: Arnd Bergmann <arnd@arndb.de>
>> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> 
> Thanks for your patch, which is now commit ed0f941022515ff4 ("ARM:
> 9404/1: arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION") in
> arm/for-next (next-20240611).
> 
> I gave this a try on my custom configs for RSK+RZA1 (RZ/A1H)
> and RZA2MEVB (RZ/A2M).  According to bloat-o-meter, enabling
> HAVE_LD_DEAD_CODE_DATA_ELIMINATION reduced kernel size by almost
> 500 KiB (-8.3%).  The figures reported in "Memory: ... available"
> were even more impressive: 1032 KiB more free memory than before.
> 
> As these boards have only 32 resp. 64 MiB of RAM, and some products
> even use RZ/A1H with just the 10 MiB of on-chip SRAM, this is a good
> improvement to have!
> Thanks!
> 
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
> Gr{oetje,eeting}s,
> 
>                          Geert
>