cpumask: add cpumask_nth_{,and,andnot}

Add cpumask_nth_{,and,andnot} as wrappers around corresponding
find functions, and use it in cpumask_local_spread().
Signed-off-by: Yury Norov <yury.norov@gmail.com>

include/linux/cpumask.h

@@ -337,6 +337,50 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
 	return i;
 }
 
+/**
+ * cpumask_nth - get the first cpu in a cpumask
+ * @srcp: the cpumask pointer
+ * @cpu: the N'th cpu to find, starting from 0
+ *
+ * Returns >= nr_cpu_ids if such cpu doesn't exist.
+ */
+static inline unsigned int cpumask_nth(unsigned int cpu, const struct cpumask *srcp)
+{
+	return find_nth_bit(cpumask_bits(srcp), nr_cpumask_bits, cpumask_check(cpu));
+}
+
+/**
+ * cpumask_nth_and - get the first cpu in 2 cpumasks
+ * @srcp1: the cpumask pointer
+ * @srcp2: the cpumask pointer
+ * @cpu: the N'th cpu to find, starting from 0
+ *
+ * Returns >= nr_cpu_ids if such cpu doesn't exist.
+ */
+static inline
+unsigned int cpumask_nth_and(unsigned int cpu, const struct cpumask *srcp1,
+							const struct cpumask *srcp2)
+{
+	return find_nth_and_bit(cpumask_bits(srcp1), cpumask_bits(srcp2),
+				nr_cpumask_bits, cpumask_check(cpu));
+}
+
+/**
+ * cpumask_nth_andnot - get the first cpu set in 1st cpumask, and clear in 2nd.
+ * @srcp1: the cpumask pointer
+ * @srcp2: the cpumask pointer
+ * @cpu: the N'th cpu to find, starting from 0
+ *
+ * Returns >= nr_cpu_ids if such cpu doesn't exist.
+ */
+static inline
+unsigned int cpumask_nth_andnot(unsigned int cpu, const struct cpumask *srcp1,
+							const struct cpumask *srcp2)
+{
+	return find_nth_andnot_bit(cpumask_bits(srcp1), cpumask_bits(srcp2),
+				nr_cpumask_bits, cpumask_check(cpu));
+}
+
 #define CPU_BITS_NONE						\
 {								\
 	[0 ... BITS_TO_LONGS(NR_CPUS)-1] = 0UL			\

lib/cpumask.c

@@ -128,23 +128,21 @@ unsigned int cpumask_local_spread(unsigned int i, int node)
 	i %= num_online_cpus();
 
 	if (node == NUMA_NO_NODE) {
-		for_each_cpu(cpu, cpu_online_mask)
-			if (i-- == 0)
-				return cpu;
+		cpu = cpumask_nth(i, cpu_online_mask);
+		if (cpu < nr_cpu_ids)
+			return cpu;
 	} else {
 		/* NUMA first. */
-		for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
-			if (i-- == 0)
-				return cpu;
-
-		for_each_cpu(cpu, cpu_online_mask) {
-			/* Skip NUMA nodes, done above. */
-			if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
-				continue;
-
-			if (i-- == 0)
-				return cpu;
-		}
+		cpu = cpumask_nth_and(i, cpu_online_mask, cpumask_of_node(node));
+		if (cpu < nr_cpu_ids)
+			return cpu;
+
+		i -= cpumask_weight_and(cpu_online_mask, cpumask_of_node(node));
+
+		/* Skip NUMA nodes, done above. */
+		cpu = cpumask_nth_andnot(i, cpu_online_mask, cpumask_of_node(node));
+		if (cpu < nr_cpu_ids)
+			return cpu;
 	}
 	BUG();
 }