From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 19 Nov 2025 17:26:57 +0000 (+0100)
Subject: cpumask: Introduce cpumask_weighted_or()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=437cb3ded25038d5280d21de489ce78c745118d5;p=thirdparty%2Fkernel%2Flinux.git

cpumask: Introduce cpumask_weighted_or()

CID management OR's two cpumasks and then calculates the weight on the
result. That's inefficient as that has to walk the same stuff twice. As
this is done with runqueue lock held, there is a real benefit of speeding
this up. Depending on the system this results in 10-20% less cycles spent
with runqueue lock held for a 4K cpumask.

Provide cpumask_weighted_or() and the corresponding bitmap functions which
return the weight of the OR result right away.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251119172549.448263340@linutronix.de
---

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 595217b7a6e71..b0395e4ccf903 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -45,6 +45,7 @@ struct device;
  *  bitmap_copy(dst, src, nbits)                *dst = *src
  *  bitmap_and(dst, src1, src2, nbits)          *dst = *src1 & *src2
  *  bitmap_or(dst, src1, src2, nbits)           *dst = *src1 | *src2
+ *  bitmap_weighted_or(dst, src1, src2, nbits)	*dst = *src1 | *src2. Returns Hamming Weight of dst
  *  bitmap_xor(dst, src1, src2, nbits)          *dst = *src1 ^ *src2
  *  bitmap_andnot(dst, src1, src2, nbits)       *dst = *src1 & ~(*src2)
  *  bitmap_complement(dst, src, nbits)          *dst = ~(*src)
@@ -165,6 +166,8 @@ bool __bitmap_and(unsigned long *dst, const unsigned long *bitmap1,
 		 const unsigned long *bitmap2, unsigned int nbits);
 void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
 		 const unsigned long *bitmap2, unsigned int nbits);
+unsigned int __bitmap_weighted_or(unsigned long *dst, const unsigned long *bitmap1,
+				  const unsigned long *bitmap2, unsigned int nbits);
 void __bitmap_xor(unsigned long *dst, const unsigned long *bitmap1,
 		  const unsigned long *bitmap2, unsigned int nbits);
 bool __bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1,
@@ -337,6 +340,18 @@ void bitmap_or(unsigned long *dst, const unsigned long *src1,
 		__bitmap_or(dst, src1, src2, nbits);
 }
 
+static __always_inline
+unsigned int bitmap_weighted_or(unsigned long *dst, const unsigned long *src1,
+				const unsigned long *src2, unsigned int nbits)
+{
+	if (small_const_nbits(nbits)) {
+		*dst = *src1 | *src2;
+		return hweight_long(*dst & BITMAP_LAST_WORD_MASK(nbits));
+	} else {
+		return __bitmap_weighted_or(dst, src1, src2, nbits);
+	}
+}
+
 static __always_inline
 void bitmap_xor(unsigned long *dst, const unsigned long *src1,
 		const unsigned long *src2, unsigned int nbits)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index ff8f41ab7ce63..feba06eb0a42e 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -728,6 +728,22 @@ void cpumask_or(struct cpumask *dstp, const struct cpumask *src1p,
 				      cpumask_bits(src2p), small_cpumask_bits);
 }
 
+/**
+ * cpumask_weighted_or - *dstp = *src1p | *src2p and return the weight of the result
+ * @dstp: the cpumask result
+ * @src1p: the first input
+ * @src2p: the second input
+ *
+ * Return: The number of bits set in the resulting cpumask @dstp
+ */
+static __always_inline
+unsigned int cpumask_weighted_or(struct cpumask *dstp, const struct cpumask *src1p,
+				 const struct cpumask *src2p)
+{
+	return bitmap_weighted_or(cpumask_bits(dstp), cpumask_bits(src1p),
+				  cpumask_bits(src2p), small_cpumask_bits);
+}
+
 /**
  * cpumask_xor - *dstp = *src1p ^ *src2p
  * @dstp: the cpumask result
diff --git a/lib/bitmap.c b/lib/bitmap.c
index b97692854966e..9dc526507875b 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -355,6 +355,12 @@ unsigned int __bitmap_weight_andnot(const unsigned long *bitmap1,
 }
 EXPORT_SYMBOL(__bitmap_weight_andnot);
 
+unsigned int __bitmap_weighted_or(unsigned long *dst, const unsigned long *bitmap1,
+				  const unsigned long *bitmap2, unsigned int bits)
+{
+	return BITMAP_WEIGHT(({dst[idx] = bitmap1[idx] | bitmap2[idx]; dst[idx]; }), bits);
+}
+
 void __bitmap_set(unsigned long *map, unsigned int start, int len)
 {
 	unsigned long *p = map + BIT_WORD(start);