linux-kernel - Re: [PATCH 06/14] cpumask: re-introduce cpumask_next{,_and}

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Message-ID: <Z4cttq0dfHnapkUI@thinkpad>
Date: Tue, 14 Jan 2025 22:38:30 -0500
From: Yury Norov <yury.norov@...il.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
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Subject: Re: [PATCH 06/14] cpumask: re-introduce cpumask_next{,_and}_wrap()

On Tue, Jan 07, 2025 at 02:28:31PM +0100, Alexander Gordeev wrote:
> On Sat, Dec 28, 2024 at 10:49:38AM -0800, Yury Norov wrote:
> 
> Hi Yury,
> 
> > cpumask_next_wrap_old() has two additional parameters, comparing to it's
> > analogue in linux/find.h find_next_bit_wrap(). The reason for that is
> > historical.
> > 
> > Before 4fe49b3b97c262 ("lib/bitmap: introduce for_each_set_bit_wrap()
> > macro"), cpumask_next_wrap() was used to implement for_each_cpu_wrap()
> > iterator. Now that the iterator is an alias to generic
> > for_each_set_bit_wrap(), the additional parameters aren't used and may
> > confuse readers.
> > 
> > All existing users call cpumask_next_wrap() in a way that makes it
> > possible to turn it to straight and simple alias to find_next_bit_wrap().
> > 
> > In a couple places kernel users opencode missing cpumask_next_and_wrap().
> > Add it as well.
> > 
> > Signed-off-by: Yury Norov <yury.norov@...il.com>
> > ---
> >  include/linux/cpumask.h | 37 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> > 
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index b267a4f6a917..18c9908d50c4 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -284,6 +284,43 @@ unsigned int cpumask_next_and(int n, const struct cpumask *src1p,
> >  		small_cpumask_bits, n + 1);
> >  }
> >  
> > +/**
> > + * cpumask_next_and_wrap - get the next cpu in *src1p & *src2p, starting from
> > + *			   @n and wrapping around, if needed
> > + * @n: the cpu prior to the place to search (i.e. return will be > @n)
> > + * @src1p: the first cpumask pointer
> > + * @src2p: the second cpumask pointer
> > + *
> > + * Return: >= nr_cpu_ids if no further cpus set in both.
> > + */
> > +static __always_inline
> > +unsigned int cpumask_next_and_wrap(int n, const struct cpumask *src1p,
> > +			      const struct cpumask *src2p)
> > +{
> > +	/* -1 is a legal arg here. */
> > +	if (n != -1)
> > +		cpumask_check(n);
> > +	return find_next_and_bit_wrap(cpumask_bits(src1p), cpumask_bits(src2p),
> > +		small_cpumask_bits, n + 1);
> > +}
> > +
> > +/*
> > + * cpumask_next_wrap - get the next cpu in *src, starting from
> > + *			   @n and wrapping around, if needed
> 
> Does it mean the search wraps a cpumask and starts from the beginning
> if the bit is not found and returns >= nr_cpu_ids if @n crosses itself?
> 
> > + * @n: the cpu prior to the place to search
> > + * @src: cpumask pointer
> > + *
> > + * Return: >= nr_cpu_ids if no further cpus set in both.
> 
> It looks like Return is a cpumask_next_and_wrap() comment leftover.
> 
> > + */
> > +static __always_inline
> > +unsigned int cpumask_next_wrap(int n, const struct cpumask *src)
> > +{
> > +	/* -1 is a legal arg here. */
> > +	if (n != -1)
> > +		cpumask_check(n);
> > +	return find_next_bit_wrap(cpumask_bits(src), small_cpumask_bits, n + 1);
> > +}
> > +
> >  /**
> >   * for_each_cpu - iterate over every cpu in a mask
> >   * @cpu: the (optionally unsigned) integer iterator
> 
> Thanks!

Thanks, I'll update the comments.