[PATCH v3 1/2] percpu: Add percpu_counter_add_local

[Jiebin Sun]

Add percpu_counter_add_local for only updating local counter
without aggregating to global counter.

This function could be used with percpu_counter_sum together if
you need high accurate counter. It could bring obvious performance
improvement if percpu_counter_add is frequently called and
percpu_counter_sum is not in the critical path.

Please use percpu_counter_add_batch instead if you need the counter
timely but not accurate and the call of percpu_counter_add_batch is
not heavy.

Signed-off-by: Jiebin Sun <jiebin.sun@xxxxxxxxx>
---
 include/linux/percpu_counter.h |  7 +++++++
 lib/percpu_counter.c           | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 01861eebed79..344d69ae0fb1 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -40,6 +40,7 @@ int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
 
 void percpu_counter_destroy(struct percpu_counter *fbc);
 void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
+void percpu_counter_add_local(struct percpu_counter *fbc, s64 amount);
 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount,
 			      s32 batch);
 s64 __percpu_counter_sum(struct percpu_counter *fbc);
@@ -138,6 +139,12 @@ percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 	preempt_enable();
 }
 
+static inline void
+percpu_counter_add_local(struct percpu_counter *fbc, s64 amount)
+{
+	percpu_counter_add(fbc, amount);
+}
+
 static inline void
 percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
 {
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index ed610b75dc32..36907eb573a8 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -72,6 +72,20 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
 }
 EXPORT_SYMBOL(percpu_counter_set);
 
+/*
+ * Recommend to use the function combined with percpu_counter_sum if you need
+ * high accurate counter. As the percpu_counter_sum add up all the percpu
+ * counter, there is no need to check batch size and sum in percpu_counter_add.
+ * If the percpu_counter_sum is infrequent used and the percpu_counter_add
+ * is in critical path, this combination could have significant performance
+ * improvement than the function percpu_counter_add_batch.
+ */
+void percpu_counter_add_local(struct percpu_counter *fbc, s64 amount)
+{
+	this_cpu_add(*fbc->counters, amount);
+}
+EXPORT_SYMBOL(percpu_counter_add_local);
+
 /*
  * This function is both preempt and irq safe. The former is due to explicit
  * preemption disable. The latter is guaranteed by the fact that the slow path
-- 
2.31.1