[NET]: Define infrastructure to keep 'inuse' changes in an efficent SMP/NUMA way.

"struct proto" currently uses an array stats[NR_CPUS] to track change on
'inuse' sockets per protocol.

If NR_CPUS is big, this means we use a big memory area for this.
Moreover, all this memory area is located on a single node on NUMA
machines, increasing memory pressure on the boot node.

In this patch, I tried to :

- Keep a fast !CONFIG_SMP implementation
- Keep a fast CONFIG_SMP implementation for often used protocols
(tcp,udp,raw,...)
- Introduce a NUMA efficient implementation

Some helper macros are defined in include/net/sock.h
These macros take into account CONFIG_SMP

If a "struct proto" is declared without using DEFINE_PROTO_INUSE /
REF_PROTO_INUSE
macros, it will automatically use a default implementation, using a
dynamically allocated percpu zone.
This default implementation will be NUMA efficient, but might use 32/64
bytes per possible cpu
because of current alloc_percpu() implementation.
However it still should be better than previous implementation based on
stats[NR_CPUS] field.

When a "struct proto" is changed to use the new macros, we use a single
static "int" percpu variable,
lowering the memory and cpu costs, still preserving NUMA efficiency.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 57 insertions, 6 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 20de3fa..5504fb9 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -560,6 +560,14 @@ struct proto {
 	void			(*unhash)(struct sock *sk);
 	int			(*get_port)(struct sock *sk, unsigned short snum);
 
+#ifdef CONFIG_SMP
+	/* Keeping track of sockets in use */
+	void			(*inuse_add)(struct proto *prot, int inc);
+	int			(*inuse_getval)(const struct proto *prot);
+	int			*inuse_ptr;
+#else
+	int			inuse;
+#endif
 	/* Memory pressure */
 	void			(*enter_memory_pressure)(void);
 	atomic_t		*memory_allocated;	/* Current allocated memory. */
@@ -592,12 +600,38 @@ struct proto {
 #ifdef SOCK_REFCNT_DEBUG
 	atomic_t		socks;
 #endif
-	struct {
-		int inuse;
-		u8  __pad[SMP_CACHE_BYTES - sizeof(int)];
-	} stats[NR_CPUS];
 };
 
+/*
+ * Special macros to let protos use a fast version of inuse{get|add}
+ * using a static percpu variable per proto instead of an allocated one,
+ * saving one dereference.
+ * This might be changed if/when dynamic percpu vars become fast.
+ */
+#ifdef CONFIG_SMP
+# define DEFINE_PROTO_INUSE(NAME)			\
+static DEFINE_PER_CPU(int, NAME##_inuse);		\
+static void NAME##_inuse_add(struct proto *prot, int inc)	\
+{							\
+	__get_cpu_var(NAME##_inuse) += inc;		\
+}							\
+							\
+static int NAME##_inuse_getval(const struct proto *prot)\
+{							\
+	int res = 0, cpu;				\
+							\
+	for_each_possible_cpu(cpu)			\
+		res += per_cpu(NAME##_inuse, cpu);	\
+	return res;					\
+}
+# define REF_PROTO_INUSE(NAME)				\
+	.inuse_add = NAME##_inuse_add,			\
+	.inuse_getval = NAME##_inuse_getval,
+#else
+# define DEFINE_PROTO_INUSE(NAME)
+# define REF_PROTO_INUSE(NAME)
+#endif
+
 extern int proto_register(struct proto *prot, int alloc_slab);
 extern void proto_unregister(struct proto *prot);
 
@@ -629,12 +663,29 @@ static inline void sk_refcnt_debug_release(const struct sock *sk)
 /* Called with local bh disabled */
 static __inline__ void sock_prot_inc_use(struct proto *prot)
 {
-	prot->stats[smp_processor_id()].inuse++;
+#ifdef CONFIG_SMP
+	prot->inuse_add(prot, 1);
+#else
+	prot->inuse++;
+#endif
 }
 
 static __inline__ void sock_prot_dec_use(struct proto *prot)
 {
-	prot->stats[smp_processor_id()].inuse--;
+#ifdef CONFIG_SMP
+	prot->inuse_add(prot, -1);
+#else
+	prot->inuse--;
+#endif
+}
+
+static __inline__ int sock_prot_inuse(struct proto *proto)
+{
+#ifdef CONFIG_SMP
+	return proto->inuse_getval(proto);
+#else
+	return proto->inuse;
+#endif
 }
 
 /* With per-bucket locks this operation is not-atomic, so that