linux-kernel - Re: [patch 1/6] Use EXTRA

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Message-ID: <20070530130603.GA25321@Krystal>
Date:	Wed, 30 May 2007 09:06:03 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [patch 1/6] Use EXTRA_RWDATA in architectures

Hi Sam,

Thanks for the comments, will integrate in my next post. I noticed that
this version was against 2.6.21-mm2, not what I thought it was
(2.6.22-rc2-mm1).

Mathieu


* Sam Ravnborg (sam@...nborg.org) wrote:
> Hi Mathieu
> > Adds a place to declare rw data that will not be far from the .data content,
> > therefore limiting the impact on cache of data declared in sections part of the
> > EXTRA_RWDATA.
> 
> No comments on the aim of the path - but a few implementation comments.
> 
> I'm glad to see asm-generic/vmlinux.lds.h used - thanks.
> The general naming is USAGE_{DATA|TEXT}
> To keep with this albait vague then established naming scheme
> please consider using: EXTRARW_DATA
> 
> 
> > Index: linux-2.6-lttng/arch/h8300/kernel/vmlinux.lds.S
> > ===================================================================
> > --- linux-2.6-lttng.orig/arch/h8300/kernel/vmlinux.lds.S	2007-05-15 18:41:05.000000000 -0400
> > +++ linux-2.6-lttng/arch/h8300/kernel/vmlinux.lds.S	2007-05-15 18:44:20.000000000 -0400
> > @@ -105,7 +105,9 @@
> >  	. = ALIGN(0x4) ;
> >  		*(.data)
> >  	. = ALIGN(0x4) ;
> > -		*(.data.*)	
> > +		*(.data.*)
> > +	. = ALIGN(0x4) ;
> > +	EXTRA_RWDATA
> 
> The usage of ALIGN seems a bit arbitary. If there is a requirement to align
> data for EXTRA_RWDATA usage then pass alignment requirment as parameter or do
> alignment in the define.
> 
> 
> > Index: linux-2.6-lttng/arch/ia64/kernel/vmlinux.lds.S
> > ===================================================================
> > --- linux-2.6-lttng.orig/arch/ia64/kernel/vmlinux.lds.S	2007-05-15 18:41:05.000000000 -0400
> > +++ linux-2.6-lttng/arch/ia64/kernel/vmlinux.lds.S	2007-05-15 18:44:20.000000000 -0400
> > @@ -214,7 +214,7 @@
> >  
> >    data : { } :data
> >    .data : AT(ADDR(.data) - LOAD_OFFSET)
> > -	{ *(.data) *(.data1) *(.gnu.linkonce.d*) CONSTRUCTORS }
> > +	{ *(.data) *(.data1) *(.gnu.linkonce.d*) EXTRA_RWDATA CONSTRUCTORS }
> >  
> Try to think of linker scripts a C-files.
> In C you would never do like this:
> 
> -	int i; struct type foo;
> +	int i; struct type foo; struct type2 bar;
> 
> You would certainly place the new variable on a new line and maybe
> fix the bad code-style in another patch.
> My point is that you should not continue the bad-taste style used here
> but just add EXTRA_RWDATA on a single line.
> 
> If no-one beats me I plan to go through all linker scrip files and add
> some sanity with respect to indent style etc. so they start to follow
> C-style for indent.
> 
> 
> > Index: linux-2.6-lttng/arch/xtensa/kernel/vmlinux.lds.S
> > ===================================================================
> > --- linux-2.6-lttng.orig/arch/xtensa/kernel/vmlinux.lds.S	2007-05-15 18:41:05.000000000 -0400
> > +++ linux-2.6-lttng/arch/xtensa/kernel/vmlinux.lds.S	2007-05-15 18:44:20.000000000 -0400
> > @@ -144,7 +144,7 @@
> >    _fdata = .;
> >    .data :
> >    {
> > -    *(.data) CONSTRUCTORS
> > +    *(.data) EXTRA_RWDATA CONSTRUCTORS
> >      . = ALIGN(XCHAL_ICACHE_LINESIZE);
> >      *(.data.cacheline_aligned)
> 
> again..
> >    }
> > Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
> > ===================================================================
> > --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h	2007-05-15 18:44:11.000000000 -0400
> > +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h	2007-05-15 18:44:20.000000000 -0400
> > @@ -143,6 +143,8 @@
> >  									\
> >  	. = ALIGN(4096);
> >  
> > +#define EXTRA_RWDATA
> > +
> Please add comment that describe the purpose of EXTRA_RWDATA - verbatim
> copy from changlog is almost enough.
> 
> 	Sam

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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