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

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Date:	Mon, 09 Dec 2013 17:15:22 +0100
From:	Tomasz Figa <t.figa@...sung.com>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	kgene.kim@...sung.com, Heiko Stuebner <heiko@...ech.de>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org,
	Doug Andersen <dianders@...omium.org>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ARM: EXYNOS: pmu: Constify data tables

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>

Best regards,
Tomasz

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