Re: [RFC] x86: merge nmi_32-64 to nmi.c

Thomas Gleixner
2008-05-17T22:34:59Z

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