Re: [PATCH v13 02/13] cpumask: Introduce cpumask_intersects_and

[Yury Norov <yury.norov@gmail.com>]

On Wed, Sep 09, 2026 at 07:26:06PM +0530, Shrikanth Hegde wrote:
> Introduce bitmap_intersects_and() to determine whether the intersection
> of three bitmaps is non-empty. Unlike cpumask_first_and_and(), this
> returns immediately when an intersecting word is found and does not
> calculate the first matching bit.
> 
> Add cpumask_intersects_and() as the corresponding cpumask wrapper.
> 
> A subsequent patch uses the helper to determine whether a task
> has a CPU that is present in its affinity mask, the preferred CPU mask,
> and task possible CPU mask.
> 
> Suggested-by: Yury Norov <yury.norov@gmail.com>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>


Reviwed-by: Yury Norov <yury.norov@gmail.com>

> ---
>  include/linux/bitmap.h  | 14 ++++++++++++++
>  include/linux/cpumask.h | 18 ++++++++++++++++++
>  lib/bitmap.c            | 17 +++++++++++++++++
>  3 files changed, 49 insertions(+)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 7df1573a409c..adafbcf2016b 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -52,6 +52,7 @@ struct device;
>   *  bitmap_complement(dst, src, nbits)          *dst = ~(*src)
>   *  bitmap_equal(src1, src2, nbits)             Are *src1 and *src2 equal?
>   *  bitmap_intersects(src1, src2, nbits)        Do *src1 and *src2 overlap?
> + *  bitmap_intersects_and(src1, src2, src3, nbits) Do *src1, *src2 and *src3 overlap?
>   *  bitmap_subset(src1, src2, nbits)            Is *src1 a subset of *src2?
>   *  bitmap_empty(src, nbits)                    Are all bits zero in *src?
>   *  bitmap_full(src, nbits)                     Are all bits set in *src?
> @@ -181,6 +182,9 @@ void __bitmap_replace(unsigned long *dst,
>  		      const unsigned long *mask, unsigned int nbits);
>  bool __bitmap_intersects(const unsigned long *bitmap1,
>  			 const unsigned long *bitmap2, unsigned int nbits);
> +bool __bitmap_intersects_and(const unsigned long *bitmap1,
> +			     const unsigned long *bitmap2,
> +			     const unsigned long *bitmap3, unsigned int nbits);
>  bool __bitmap_subset(const unsigned long *bitmap1,
>  		     const unsigned long *bitmap2, unsigned int nbits);
>  unsigned int __bitmap_weight(const unsigned long *bitmap, unsigned int nbits);
> @@ -445,6 +449,16 @@ bool bitmap_intersects(const unsigned long *src1, const unsigned long *src2, uns
>  		return __bitmap_intersects(src1, src2, nbits);
>  }
>  
> +static __always_inline
> +bool bitmap_intersects_and(const unsigned long *src1, const unsigned long *src2,
> +			   const unsigned long *src3, unsigned int nbits)
> +{
> +	if (small_const_nbits(nbits))
> +		return ((*src1 & *src2 & *src3) & BITMAP_LAST_WORD_MASK(nbits)) != 0;
> +	else
> +		return __bitmap_intersects_and(src1, src2, src3, nbits);
> +}
> +
>  static __always_inline
>  bool bitmap_subset(const unsigned long *src1, const unsigned long *src2, unsigned int nbits)
>  {
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index 4c8bb6953107..7c8f16797f94 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -824,6 +824,24 @@ bool cpumask_intersects(const struct cpumask *src1p, const struct cpumask *src2p
>  						      small_cpumask_bits);
>  }
>  
> +/**
> + * cpumask_intersects_and - (*src1p & *src2p & *src3p) != 0
> + * @src1p: the first input
> + * @src2p: the second input
> + * @src3p: the third input
> + *
> + * Return: true if AND of the three cpumasks is non-empty,
> + *	   otherwise false
> + */
> +static __always_inline
> +bool cpumask_intersects_and(const struct cpumask *src1p,
> +			    const struct cpumask *src2p,
> +			    const struct cpumask *src3p)
> +{
> +	return bitmap_intersects_and(cpumask_bits(src1p), cpumask_bits(src2p),
> +				 cpumask_bits(src3p), small_cpumask_bits);
> +}
> +
>  /**
>   * cpumask_subset - (*src1p & ~*src2p) == 0
>   * @src1p: the first input
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index ed685127a107..d1cb8a507c60 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -308,6 +308,23 @@ bool __bitmap_intersects(const unsigned long *bitmap1,
>  }
>  EXPORT_SYMBOL(__bitmap_intersects);
>  
> +bool __bitmap_intersects_and(const unsigned long *bitmap1,
> +			     const unsigned long *bitmap2,
> +			     const unsigned long *bitmap3, unsigned int bits)
> +{
> +	unsigned int k, lim = bits / BITS_PER_LONG;
> +
> +	for (k = 0; k < lim; ++k)
> +		if (bitmap1[k] & bitmap2[k] & bitmap3[k])
> +			return true;
> +
> +	if (bits % BITS_PER_LONG)
> +		if ((bitmap1[k] & bitmap2[k] & bitmap3[k]) & BITMAP_LAST_WORD_MASK(bits))
> +			return true;
> +	return false;
> +}
> +EXPORT_SYMBOL(__bitmap_intersects_and);
> +
>  bool __bitmap_subset(const unsigned long *bitmap1,
>  		     const unsigned long *bitmap2, unsigned int bits)
>  {
> -- 
> 2.52.0