1 files changed, 74 insertions, 0 deletions
diff --git a/include/linux/pcounter.h b/include/linux/pcounter.h
new file mode 100644
index 0000000..a82d9f2
--- /dev/null
+++ b/include/linux/pcounter.h
@@ -0,0 +1,74 @@
+#ifndef __LINUX_PCOUNTER_H
+#define __LINUX_PCOUNTER_H
+/*
+ * Using a dynamic percpu 'int' variable has a cost :
+ * 1) Extra dereference
+ * Current per_cpu_ptr() implementation uses an array per 'percpu variable'.
+ * 2) memory cost of NR_CPUS*(32+sizeof(void *)) instead of num_possible_cpus()*4
+ *
+ * This pcounter implementation is an abstraction to be able to use
+ * either a static or a dynamic per cpu variable.
+ * One dynamic per cpu variable gets a fast & cheap implementation, we can
+ * change pcounter implementation too.
+ */
+struct pcounter {
+#ifdef CONFIG_SMP
+	void		(*add)(struct pcounter *self, int inc);
+	int		(*getval)(const struct pcounter *self, int cpu);
+	int		*per_cpu_values;
+#else
+	int		val;
+#endif
+};
+
+#ifdef CONFIG_SMP
+#include <linux/percpu.h>
+
+#define DEFINE_PCOUNTER(NAME)						\
+static DEFINE_PER_CPU(int, NAME##_pcounter_values);			\
+static void NAME##_pcounter_add(struct pcounter *self, int val)		\
+{									\
+       __get_cpu_var(NAME##_pcounter_values) += val;			\
+}									\
+static int NAME##_pcounter_getval(const struct pcounter *self, int cpu)	\
+{									\
+	return per_cpu(NAME##_pcounter_values, cpu);			\
+}									\
+
+#define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER)		\
+	MEMBER = {						\
+		.add	= NAME##_pcounter_add,			\
+		.getval = NAME##_pcounter_getval,		\
+	}
+
+
+static inline void pcounter_add(struct pcounter *self, int inc)
+{
+	self->add(self, inc);
+}
+
+extern int pcounter_getval(const struct pcounter *self);
+extern int pcounter_alloc(struct pcounter *self);
+extern void pcounter_free(struct pcounter *self);
+
+
+#else /* CONFIG_SMP */
+
+static inline void pcounter_add(struct pcounter *self, int inc)
+{
+	self->val += inc;
+}
+
+static inline int pcounter_getval(const struct pcounter *self)
+{
+	return self->val;
+}
+
+#define DEFINE_PCOUNTER(NAME)
+#define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER)
+#define pcounter_alloc(self) 0
+#define pcounter_free(self)
+
+#endif /* CONFIG_SMP */
+
+#endif /* __LINUX_PCOUNTER_H */