[LIB]: Introduce struct pcounter
This just generalises what was introduced by Eric Dumazet for the struct proto
inuse field in 286ab3d46058840d68e5d7d52e316c1f7e98c59f:
[NET]: Define infrastructure to keep 'inuse' changes in an efficent SMP/NUMA way.
Please look at the comment in there to see the rationale.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/pcounter.h b/include/linux/pcounter.h
new file mode 100644
index 0000000..620aade
--- /dev/null
+++ b/include/linux/pcounter.h
@@ -0,0 +1,102 @@
+#ifndef __LINUX_PCOUNTER_H
+#define __LINUX_PCOUNTER_H
+
+struct pcounter {
+#ifdef CONFIG_SMP
+ void (*add)(struct pcounter *self, int inc);
+ int (*getval)(const struct pcounter *self);
+ int *per_cpu_values;
+#else
+ int val;
+#endif
+};
+
+/*
+ * Special macros to let pcounters use a fast version of {getvalue|add}
+ * using a static percpu variable per pcounter instead of an allocated one,
+ * saving one dereference.
+ * This might be changed if/when dynamic percpu vars become fast.
+ */
+#ifdef CONFIG_SMP
+#include <linux/cpumask.h>
+#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 inc) \
+{ \
+ __get_cpu_var(NAME##_pcounter_values) += inc; \
+} \
+ \
+static int NAME##_pcounter_getval(const struct pcounter *self) \
+{ \
+ int res = 0, cpu; \
+ \
+ for_each_possible_cpu(cpu) \
+ res += per_cpu(NAME##_pcounter_values, cpu); \
+ return res; \
+}
+
+#define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER) \
+ MEMBER = { \
+ .add = NAME##_pcounter_add, \
+ .getval = NAME##_pcounter_getval, \
+ }
+
+extern void pcounter_def_add(struct pcounter *self, int inc);
+extern int pcounter_def_getval(const struct pcounter *self);
+
+static inline int pcounter_alloc(struct pcounter *self)
+{
+ int rc = 0;
+ if (self->add == NULL) {
+ self->per_cpu_values = alloc_percpu(int);
+ if (self->per_cpu_values != NULL) {
+ self->add = pcounter_def_add;
+ self->getval = pcounter_def_getval;
+ } else
+ rc = 1;
+ }
+ return rc;
+}
+
+static inline void pcounter_free(struct pcounter *self)
+{
+ if (self->per_cpu_values != NULL) {
+ free_percpu(self->per_cpu_values);
+ self->per_cpu_values = NULL;
+ self->getval = NULL;
+ self->add = NULL;
+ }
+}
+
+static inline void pcounter_add(struct pcounter *self, int inc)
+{
+ self->add(self, inc);
+}
+
+static inline int pcounter_getval(const struct pcounter *self)
+{
+ return self->getval(self);
+}
+
+#else /* CONFIG_SMP */
+
+static inline void pcounter_add(struct pcounter *self, int inc)
+{
+ self->value += 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 */