[tip: sched/core] cpumask: Introduce cpumask_intersects_and

[tip-bot2 for Shrikanth Hegde]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     cfb463b7172dca2f29b2221b71b54890f268e3fb
Gitweb:        https://git.kernel.org/tip/cfb463b7172dca2f29b2221b71b54890f268e3fb
Author:        Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
AuthorDate:    Mon, 28 Sep 2026 11:07:17 +05:30
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 28 Sep 2026 08:44:40 +02:00

cpumask: Introduce cpumask_intersects_and

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@xxxxxxxxx>
Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
Reviwed-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Yury Norov <yury.norov@xxxxxxxxx>
Link: https://patch.msgid.link/20260928053728.797539-3-sshegde@xxxxxxxxxxxxx
---
 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 7df1573..adafbcf 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);
@@ -446,6 +450,16 @@ bool bitmap_intersects(const unsigned long *src1, const unsigned long *src2, uns
 }
 
 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)
 {
 	if (small_const_nbits(nbits))
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 4c8bb69..7c8f167 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -825,6 +825,24 @@ bool cpumask_intersects(const struct cpumask *src1p, const struct cpumask *src2p
 }
 
 /**
+ * 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
  * @src2p: the second input
diff --git a/lib/bitmap.c b/lib/bitmap.c
index ed68512..d1cb8a5 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)
 {