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

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/bitmap.c b/lib/bitmap.c
index b97692854966..9dc526507875 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);