[PATCH 3.16 003/192] sched/fair, cpumask: Export for_each_cpu_wrap()

Ben Hutchings
2017-10-09T13:57:15Z

From: Peter Zijlstra <peterz@infradead.org>

commit c743f0a5c50f2fcbc628526279cfa24f3dabe182 upstream.

More users for for_each_cpu_wrap() have appeared. Promote the construct
to generic cpumask interface.

The implementation is slightly modified to reduce arguments.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Lauro Ramos Venancio <lvenanci@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: lwang@redhat.com
Link: http://lkml.kernel.org/r/20170414122005.o35me2h5nowqkxbv@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.16: there's no old version of the function to delete]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -225,6 +225,23 @@ int cpumask_set_cpu_local_first(int i, i
(cpu) = cpumask_next_zero((cpu), (mask)), \
(cpu) < nr_cpu_ids;)

+extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap);
+
+/**
+ * for_each_cpu_wrap - iterate over every cpu in a mask, starting at a specified location
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask: the cpumask poiter
+ * @start: the start location
+ *
+ * The implementation does not assume any bit in @mask is set (including @start).
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_wrap(cpu, mask, start) \
+ for ((cpu) = cpumask_next_wrap((start)-1, (mask), (start), false); \
+ (cpu) < nr_cpumask_bits; \
+ (cpu) = cpumask_next_wrap((cpu), (mask), (start), true))
+
/**
* for_each_cpu_and - iterate over every cpu in both masks
* @cpu: the (optionally unsigned) integer iterator
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -63,6 +63,38 @@ int cpumask_any_but(const struct cpumask
return i;
}

+/**
+ * cpumask_next_wrap - helper to implement for_each_cpu_wrap
+ * @n: the cpu prior to the place to search
+ * @mask: the cpumask pointer
+ * @start: the start point of the iteration
+ * @wrap: assume @n crossing @start terminates the iteration
+ *
+ * Returns >= nr_cpu_ids on completion
+ *
+ * Note: the @wrap argument is required for the start condition when
+ * we cannot assume @start is set in @mask.
+ */
+int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
+{
+ int next;
+
+again:
+ next = cpumask_next(n, mask);
+
+ if (wrap && n < start && next >= start) {
+ return nr_cpumask_bits;
+
+ } else if (next >= nr_cpumask_bits) {
+ wrap = true;
+ n = -1;
+ goto again;
+ }
+
+ return next;
+}
+EXPORT_SYMBOL(cpumask_next_wrap);
+
/* These are not inline because of header tangles. */
#ifdef CONFIG_CPUMASK_OFFSTACK
/**