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

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Date:	Sat, 17 May 2008 23:48:25 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Tom Spink <tspink@...il.com>, Cyrill Gorcunov <gorcunov@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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

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.
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