Re: [PATCH 01/10] cpumask: Introduce cpumask_any_online_but

[Vikas Shivappa]

On Wed, 24 Jun 2015, Thomas Gleixner wrote:

> On Tue, 23 Jun 2015, Vikas Shivappa wrote:
> > There is currently no cpumask helper function to pick a "random" cpu
> > from a mask which is also online.
> >
> > cpumask_any_online_but() does that which is similar to cpumask_any_but()
> > but also returns a cpu that is online.
> >
> > Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
> > ---
> >  include/linux/cpumask.h | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index 27e285b..ea63b65 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -548,6 +548,24 @@ static inline void cpumask_copy(struct cpumask *dstp,
> >  #define cpumask_of(cpu) (get_cpu_mask(cpu))
> >
> >  /**
> > + * cpumask_any_online_but - return a "random"  and online cpu in a cpumask,
> > + * but not this one
> > + * @mask: the input mask to search
> > + * @cpu: the cpu to ignore
> > + *
> > + * Returns >= nr_cpu_ids if no cpus set.
> > +*/
> > +static inline unsigned int cpumask_any_online_but(const struct cpumask *mask,
> > +					   unsigned int cpu)
> > +{
> > +	static cpumask_t tmp;
>
> How is that supposed to work?
>
> You cannot expect, that all potential users of this function are
> magically serialized.

I am trying do something wierd with this API. trying to do 
cpumask_and_any_but. But anything with 'and' operation, usually the caller 
supplies the dst. Guess I can remove this API altogether and 'and' the online 
and package cpu masks during hot cpu notifications.

Thanks,
Vikas

> > +
> > +	cpumask_and(&tmp, cpu_online_mask, mask);
> > +	cpumask_clear_cpu(cpu, &tmp);
> > +	return cpumask_any(&tmp);
>
> Thanks,
>
> 	tglx
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