sched/fair, cpumask: Export for_each_cpu_wrap()

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 3.2: there's no old version of the function to delete]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 4f7a632..1b6ce8c 100644 (file)
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -216,6 +216,23 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu);
                (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

diff --git a/lib/cpumask.c b/lib/cpumask.c
index af3e581..7018459 100644 (file)
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -75,6 +75,38 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
        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
 /**