linux-kernel - Re: [PATCH 1/3] ARM: EXYNOS: pmu: Constify data tables

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Message-ID: <52A62F68.906@samsung.com>
Date:	Tue, 10 Dec 2013 06:00:24 +0900
From:	Kukjin Kim <kgene.kim@...sung.com>
To:	Tomasz Figa <t.figa@...sung.com>
CC:	Daniel Kurtz <djkurtz@...omium.org>,
	linux-samsung-soc@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Heiko Stuebner <heiko@...ech.de>,
	Doug Andersen <dianders@...omium.org>,
	linux-kernel@...r.kernel.org,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	kgene.kim@...sung.com, Ben Dooks <ben-linux@...ff.org>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] ARM: EXYNOS: pmu: Constify data tables

On 12/10/13 01:15, Tomasz Figa wrote:
> On Tuesday 10 of December 2013 00:11:40 Daniel Kurtz wrote:
>> Hi Tomasz,
>>
>> Thank you for the reviews.
>>
>> On Dec 9, 2013 5:15 AM, "Tomasz Figa"<t.figa@...sung.com>  wrote:
>>>
>>> Hi Daniel,
>>>
>>> On Thursday 21 of November 2013 02:21:24 Daniel Kurtz wrote:
>>>> These tables are all immutable, make them const to save 4416 bytes of RAM.
>>>>
>>>> size arch/arm/mach-exynos/pmu.o
>>>>     text          data     bss
>>>>      848          4420       4         // before
>>>>     5264             4       4         // after
>>>
>>> I'm not sure where the mentioned saving of RAM is. Moving data between
>>> sections is not supposed to make it use less memory, I believe.
>>
>> You are correct.  This was my misunderstanding from doing too much
>> work with microcontrollers, where .text sections are accessed in place
>> from FLASH for code and const data, but .data memory is copied from a
>> FLASH section to a second RAM section at init for access at runtime.
>> Most modern Linux systems copy/decompress their code and data sections
>> from external storage to RAM anyway, so there is no actual memory
>> savings (except potentially the compiler may be able to optimize a bit
>> more with the const hint).
>>
>>>
>>> Anyway, it's a good practice to mark constant data as const, to disallow
>>> changing them at runtime by mistake, so the patch is fine. Except some
>>> issues I commented on inline.
>>
>> Were there supposed to be inline comments?  I don't see any.
>
> Oops, sorry for this, forgot to remove the last sentence. I initially had
> one question about the constant pointers below, but I read through the
> full code again and answered it myself.
>
> The patch is fine.
>
> Reviewed-by: Tomasz Figa<t.figa@...sung.com>
>
OK, applied 1 to 3 patches into cleanup.

Thanks,
Kukjin
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