From 6cc18331a987c4a29d66b9c4fd292587fba4d7bd Mon Sep 17 00:00:00 2001
From: Yury Norov <yury.norov@gmail.com>
Date: Mon, 19 Sep 2022 14:05:56 -0700
Subject: lib/find_bit: add find_next{,_and}_bit_wrap

The helper is better optimized for the worst case: in case of empty
cpumask, current code traverses 2 * size:

  next = cpumask_next_and(prev, src1p, src2p);
  if (next >= nr_cpu_ids)
  	next = cpumask_first_and(src1p, src2p);

At bitmap level we can stop earlier after checking 'size + offset' bits.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 include/linux/find.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

(limited to 'include/linux/find.h')

diff --git a/include/linux/find.h b/include/linux/find.h
index 128615a3f93e..77c087b7a451 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -290,6 +290,52 @@ unsigned long find_last_bit(const unsigned long *addr, unsigned long size)
 }
 #endif
 
+/**
+ * find_next_and_bit_wrap - find the next set bit in both memory regions
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit, or first set bit up to @offset
+ * If no bits are set, returns @size.
+ */
+static inline
+unsigned long find_next_and_bit_wrap(const unsigned long *addr1,
+					const unsigned long *addr2,
+					unsigned long size, unsigned long offset)
+{
+	unsigned long bit = find_next_and_bit(addr1, addr2, size, offset);
+
+	if (bit < size)
+		return bit;
+
+	bit = find_first_and_bit(addr1, addr2, offset);
+	return bit < offset ? bit : size;
+}
+
+/**
+ * find_next_bit_wrap - find the next set bit in both memory regions
+ * @addr: The first address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit, or first set bit up to @offset
+ * If no bits are set, returns @size.
+ */
+static inline
+unsigned long find_next_bit_wrap(const unsigned long *addr,
+					unsigned long size, unsigned long offset)
+{
+	unsigned long bit = find_next_bit(addr, size, offset);
+
+	if (bit < size)
+		return bit;
+
+	bit = find_first_bit(addr, offset);
+	return bit < offset ? bit : size;
+}
+
 /**
  * find_next_clump8 - find next 8-bit clump with set bits in a memory region
  * @clump: location to store copy of found clump
-- 
cgit