net: move napi_hash[] into read mostly section

We do not often add/delete a napi context.
Moving napi_hash[] into read mostly section avoids potential false sharing.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/hashtable.h

@@ -16,6 +16,10 @@
 	struct hlist_head name[1 << (bits)] =					\
 			{ [0 ... ((1 << (bits)) - 1)] = HLIST_HEAD_INIT }
 
+#define DEFINE_READ_MOSTLY_HASHTABLE(name, bits)				\
+	struct hlist_head name[1 << (bits)] __read_mostly =			\
+			{ [0 ... ((1 << (bits)) - 1)] = HLIST_HEAD_INIT }
+
 #define DECLARE_HASHTABLE(name, bits)                                   	\
 	struct hlist_head name[1 << (bits)]
 

net/core/dev.c

@@ -184,7 +184,7 @@ EXPORT_SYMBOL(dev_base_lock);
 static DEFINE_SPINLOCK(napi_hash_lock);
 
 static unsigned int napi_gen_id = NR_CPUS;
-static DEFINE_HASHTABLE(napi_hash, 8);
+static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8);
 
 static seqcount_t devnet_rename_seq;