linux-kernel - Re: [PATCH] Make for_each_cpu

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Date:	Sun, 11 May 2008 18:19:39 +0200
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	"Matthew Wilcox" <matthew@....cx>,
	"Alexander van Heukelum" <heukelum@...lshack.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Paul Jackson" <pj@....com>, "Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"linux-arch" <linux-arch@...r.kernel.org>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Make for_each_cpu_mask a bit smaller


On Sun, 11 May 2008 09:24:40 -0600, "Matthew Wilcox" <matthew@....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.

Greetings,
    Alexander
-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

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