Re: [PATCH 06/14] cpumask: re-introduce cpumask_next{,_and}_wrap()

Alexander Gordeev
2025-01-07T13:29:34Z

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@gmail.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!