[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>

1 files changed, 102 insertions, 0 deletions

diff --git a/include/linux/pcounter.h b/include/linux/pcounter.h
new file mode 100644
index 000000000000..620aaded4e94
--- /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 */