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Subject[PATCH 2/4] cpumask: Make cpumask_any() truly random
Date
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@arm.com>
CC: Juri Lelli <juri.lelli@redhat.com>
CC: Vincent Guittot <vincent.guittot@linaro.org>
CC: Dietmar Eggemann <dietmar.eggemann@arm.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ben Segall <bsegall@google.com>
CC: Mel Gorman <mgorman@suse.de>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Yury Norov <yury.norov@gmail.com>
CC: Paul Turner <pjt@google.com>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Josh Don <joshdon@google.com>
CC: Pavan Kondeti <pkondeti@codeaurora.org>
CC: linux-kernel@vger.kernel.org
---
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
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