[PATCH 2/4] cpumask: Make cpumask_any() truly random

[Qais Yousef]

Commit 46a87b3851f0 ("sched/core: Distribute tasks within affinity masks")
added a new cpumask_any_and_distribute() which truly returns a random
cpu within the mask.

Previous patch renamed the function to cpumask_any_and(), so that old
users can take advantage of the new randomness behavior.

Build up on that, and let cpumask_any() truly random too by re-using the
logic from cpumask_any_and().

Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>
CC: Juri Lelli <juri.lelli@xxxxxxxxxx>
CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ben Segall <bsegall@xxxxxxxxxx>
CC: Mel Gorman <mgorman@xxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Yury Norov <yury.norov@xxxxxxxxx>
CC: Paul Turner <pjt@xxxxxxxxxx>
CC: Alexey Dobriyan <adobriyan@xxxxxxxxx>
CC: Josh Don <joshdon@xxxxxxxxxx>
CC: Pavan Kondeti <pkondeti@xxxxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/cpumask.h | 14 ++++++--------
 lib/cpumask.c           | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index e4d6d140a67c..7fb25d256043 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -194,6 +194,11 @@ static inline unsigned int cpumask_local_spread(unsigned int i, int node)
 	return 0;
 }
 
+static inline int cpumask_any(const struct cpumask *src1p)
+{
+	return 0;
+}
+
 static inline int cpumask_any_and(const struct cpumask *src1p,
 				  const struct cpumask *src2p)
 {
@@ -251,6 +256,7 @@ static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp)
 int cpumask_next_and(int n, const struct cpumask *, const struct cpumask *);
 int cpumask_any_but(const struct cpumask *mask, unsigned int cpu);
 unsigned int cpumask_local_spread(unsigned int i, int node);
+int cpumask_any(const struct cpumask *srcp);
 int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p);
 
 /**
@@ -600,14 +606,6 @@ static inline void cpumask_copy(struct cpumask *dstp,
 	bitmap_copy(cpumask_bits(dstp), cpumask_bits(srcp), nr_cpumask_bits);
 }
 
-/**
- * cpumask_any - pick a "random" cpu from *srcp
- * @srcp: the input cpumask
- *
- * Returns >= nr_cpu_ids if no cpus set.
- */
-#define cpumask_any(srcp) cpumask_first(srcp)
-
 /**
  * cpumask_first_and - return the first cpu from *srcp1 & *srcp2
  * @src1p: the first input
diff --git a/lib/cpumask.c b/lib/cpumask.c
index b527a153b023..bcac63e45374 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -259,3 +259,27 @@ int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p)
 	return next;
 }
 EXPORT_SYMBOL(cpumask_any_and);
+
+/**
+ * cpumask_any - pick a "random" cpu from *srcp
+ * @srcp: the input cpumask
+ *
+ * Returns >= nr_cpu_ids if no cpus set.
+ */
+int cpumask_any(const struct cpumask *srcp)
+{
+	int next, prev;
+
+	/* NOTE: our first selection will skip 0. */
+	prev = __this_cpu_read(distribute_cpu_mask_prev);
+
+	next = cpumask_next(prev, srcp);
+	if (next >= nr_cpu_ids)
+		next = cpumask_first(srcp);
+
+	if (next < nr_cpu_ids)
+		__this_cpu_write(distribute_cpu_mask_prev, next);
+
+	return next;
+}
+EXPORT_SYMBOL(cpumask_any);
-- 
2.17.1