linux-kernel - Re: [RFC] x86: merge nmi

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Date:	Sun, 18 May 2008 14:09:55 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mikael Pettersson <mikpe@...uu.se>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Tom Spink <tspink@...il.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jirislaby@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC] x86: merge nmi_32-64 to nmi.c

[Thomas Gleixner - Sun, May 18, 2008 at 12:34:15AM +0200]
| On Sat, 17 May 2008, Mikael Pettersson wrote:
| > Maciej W. Rozycki writes:
| >  > On Sat, 17 May 2008, Tom Spink wrote:
| >  > 
| >  > > static inline unsigned int get_nmi_count(int cpu)
| >  > > {
| >  > > #ifdef CONFIG_X86_64
| >  > >         return cpu_pda(cpu)->__nmi_count;
| >  > > #else
| >  > >         return nmi_count(cpu);
| >  > > #endif
| >  > > }
| >  > > 
| >  > > I know it introduces a lot of these conditionals, but at least there
| >  > > is one place to look for the get_nmi_count function, instead of
| >  > > searching for all variants of the function.
| >  > 
| >  >  Well, I suppose some header should provide a definition like:
| >  > 
| >  > #ifdef CONFIG_X86_64
| >  > #define cpu_x86_64 1
| >  > #else
| >  > #define cpu_x86_64 0
| >  > #endif
| >  > 
| >  > and the you can remove the horrible #ifdef clutter and make the quoted 
| >  > function look like:
| >  > 
| >  > static inline unsigned int get_nmi_count(int cpu)
| >  > {
| >  > 	return cpu_x86_64 ? cpu_pda(cpu)->__nmi_count : nmi_count(cpu);
| >  > }
| >  > 
| >  > Much better -- isn't it?
| > 
| > IMO, no, the #ifdef is preferable.
| > 
| > Why? Because the #ifdef is a very visible signal to the platform
| > people that there are (in this case) subarch differences that force
| > "clients" to behave differently on different subarchs. By removing
| > the #ifdef you're IMO making it less likely for the platform people
| > to take notice and work towards eliminating those differences.
| 
| The #ifdef is a poor choice. Maciej is damned right, that the single
| function with a clear distinction of the return value is better in
| terms of readability and maintenance.
| 
| As I said before, We can make this more visible with an uppercase
| CONFIG_WHATEVER instaed of the innocent cpu_x86_64 one, but both
| solutions are better than #ifdefs and provide simple grepable
| patterns.
| 
| The awareness of those differences does not depend at all on an
| #ifdef. Developers who are aware of the platform differences prefer a
| readable not ifdef poluted code base. People who need to be poked into
| the difference via an #ifdef are probably not those who can actually
| clean it up.
| 
| Thanks,
| 
| 	tglx
| 

Btw Thomas, is there any reason why can't we add do_panic in die_nmi
on 32bit? And that would help us to add "panic" boot option on 32bits
as well.

		- Cyrill -
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