net: add napi_id and hash

Adds a napi_id and a hashing mechanism to lookup a napi by id.
This will be used by subsequent patches to implement low latency
Ethernet device polling.
Based on a code sample by Eric Dumazet.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 8f967e3..39bbd46 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -324,12 +324,15 @@ struct napi_struct {
        struct sk_buff          *gro_list;
        struct sk_buff          *skb;
        struct list_head        dev_list;
+       struct hlist_node       napi_hash_node;
+       unsigned int            napi_id;
 };
 
 enum {
        NAPI_STATE_SCHED,       /* Poll is scheduled */
        NAPI_STATE_DISABLE,     /* Disable pending */
        NAPI_STATE_NPSVC,       /* Netpoll - don't dequeue from poll_list */
+       NAPI_STATE_HASHED,      /* In NAPI hash */
 };
 
 enum gro_result {
@@ -446,6 +449,32 @@ extern void __napi_complete(struct napi_struct *n);
 extern void napi_complete(struct napi_struct *n);
 
 /**
+ *     napi_by_id - lookup a NAPI by napi_id
+ *     @napi_id: hashed napi_id
+ *
+ * lookup @napi_id in napi_hash table
+ * must be called under rcu_read_lock()
+ */
+extern struct napi_struct *napi_by_id(unsigned int napi_id);
+
+/**
+ *     napi_hash_add - add a NAPI to global hashtable
+ *     @napi: napi context
+ *
+ * generate a new napi_id and store a @napi under it in napi_hash
+ */
+extern void napi_hash_add(struct napi_struct *napi);
+
+/**
+ *     napi_hash_del - remove a NAPI from global table
+ *     @napi: napi context
+ *
+ * Warning: caller must observe rcu grace period
+ * before freeing memory containing @napi
+ */
+extern void napi_hash_del(struct napi_struct *napi);
+
+/**
  *     napi_disable - prevent NAPI from scheduling
  *     @n: napi context
  *

diff --git a/net/core/dev.c b/net/core/dev.c
index 9c18557..fa007db 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -129,6 +129,7 @@
 #include <linux/inetdevice.h>
 #include <linux/cpu_rmap.h>
 #include <linux/static_key.h>
+#include <linux/hashtable.h>
 
 #include "net-sysfs.h"
 
@@ -166,6 +167,12 @@ static struct list_head offload_base __read_mostly;
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
+/* protects napi_hash addition/deletion and napi_gen_id */
+static DEFINE_SPINLOCK(napi_hash_lock);
+
+static unsigned int napi_gen_id;
+static DEFINE_HASHTABLE(napi_hash, 8);
+
 seqcount_t devnet_rename_seq;
 
 static inline void dev_base_seq_inc(struct net *net)
@@ -4136,6 +4143,58 @@ void napi_complete(struct napi_struct *n)
 }
 EXPORT_SYMBOL(napi_complete);
 
+/* must be called under rcu_read_lock(), as we dont take a reference */
+struct napi_struct *napi_by_id(unsigned int napi_id)
+{
+       unsigned int hash = napi_id % HASH_SIZE(napi_hash);
+       struct napi_struct *napi;
+
+       hlist_for_each_entry_rcu(napi, &napi_hash[hash], napi_hash_node)
+               if (napi->napi_id == napi_id)
+                       return napi;
+
+       return NULL;
+}
+EXPORT_SYMBOL_GPL(napi_by_id);
+
+void napi_hash_add(struct napi_struct *napi)
+{
+       if (!test_and_set_bit(NAPI_STATE_HASHED, &napi->state)) {
+
+               spin_lock(&napi_hash_lock);
+
+               /* 0 is not a valid id, we also skip an id that is taken
+                * we expect both events to be extremely rare
+                */
+               napi->napi_id = 0;
+               while (!napi->napi_id) {
+                       napi->napi_id = ++napi_gen_id;
+                       if (napi_by_id(napi->napi_id))
+                               napi->napi_id = 0;
+               }
+
+               hlist_add_head_rcu(&napi->napi_hash_node,
+                       &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
+
+               spin_unlock(&napi_hash_lock);
+       }
+}
+EXPORT_SYMBOL_GPL(napi_hash_add);
+
+/* Warning : caller is responsible to make sure rcu grace period
+ * is respected before freeing memory containing @napi
+ */
+void napi_hash_del(struct napi_struct *napi)
+{
+       spin_lock(&napi_hash_lock);
+
+       if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state))
+               hlist_del_rcu(&napi->napi_hash_node);
+
+       spin_unlock(&napi_hash_lock);
+}
+EXPORT_SYMBOL_GPL(napi_hash_del);
+
 void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
                    int (*poll)(struct napi_struct *, int), int weight)
 {