Re: [PATCH] Make for_each_cpu_mask a bit smaller

[Matthew Wilcox <matthew@wil.cx>]

On Sun, May 11, 2008 at 06:19:39PM +0200, Alexander van Heukelum wrote:
> 
> On Sun, 11 May 2008 09:24:40 -0600, "Matthew Wilcox" <matthew@wil.cx>
> said:
> > On Sun, May 11, 2008 at 03:50:39PM +0200, Alexander van Heukelum wrote:
> > >  #if NR_CPUS > 1
> > > -#define for_each_cpu_mask(cpu, mask)		\
> > > -	for ((cpu) = first_cpu(mask);		\
> > > -		(cpu) < NR_CPUS;		\
> > > -		(cpu) = next_cpu((cpu), (mask)))
> > > +#define for_each_cpu_mask(cpu, mask)				\
> > > +	for ((cpu) = 0;						\
> > > +		(cpu) = find_next_cpu_mask((cpu), &(mask)),	\
> > > +		(cpu) < NR_CPUS; (cpu)++)
> > 
> > For anyone else having similar cognitive dissonance while reading this
> > thinking "But won't the first call to find_next_cpu_mask return a number
> > > 0", the answer is "no, find_next_bit returns the next set bit that's
> > >= the number passed in, which is why we need both the cpu++ and
> > find_next_cpu_mask".  
> 
> That's how it works, indeed.
> 
> > > +int find_next_cpu_mask(int n, const cpumask_t *srcp)
> > > +{
> > > +	return find_next_bit(srcp->bits, NR_CPUS, n);
> > > +}
> > > +EXPORT_SYMBOL(find_next_cpu_mask);
> > 
> > Maybe a better name for this function would help.  I can't think of a
> > good one right now though.
> 
> I can't think of a better name, and there is find_next_bit of which
> find_next_cpu_mask is just a wrapper. I think the name is good enough.

How about doing it this way?

#define for_each_cpu_mask(cpu, mask)				\
	for ((cpu) = -1;					\
	     (cpu) < NR_CPUS;					\
	     (cpu) = find_next_cpu_mask((cpu), &(mask)))

int find_next_cpu_mask(int n, const cpumask_t *srcp)
{
	return find_next_bit(srcp->bits, NR_CPUS, ++n);
}

That actually behaves the way I'd expect a function called
'find_next_cpu_mask' to work.  It also abuses the 'for' condtion
less and might take a little less text space.

-- 
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