macvtap: eliminate linear search

Linear search were used in both get_slot() and macvtap_get_queue(), this is
because:

- macvtap didn't reshuffle the array of taps when create or destroy a queue, so
  when adding a new queue, macvtap must do linear search to find a location for
  the new queue. This will also complicate the TUNSETQUEUE implementation for
  multiqueue API.
- the queue itself didn't track the queue index, so the we must do a linear
  search in the array to find the location of a existed queue.

The solution is straightforward: reshuffle the array and introduce a queue_index
to macvtap_queue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index d18130b3fe0d93e09c6e1ab25ca41bc412984bd0..5ccba99b15f4c1ea53e3cb6522e0598a00a845e5 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -44,6 +44,7 @@ struct macvtap_queue {
        struct macvlan_dev __rcu *vlan;
        struct file *file;
        unsigned int flags;
+       u16 queue_index;
 };
 
 static struct proto macvtap_proto = {
@@ -84,30 +85,10 @@ static const struct proto_ops macvtap_socket_ops;
  */
 static DEFINE_SPINLOCK(macvtap_lock);
 
-/*
- * get_slot: return a [unused/occupied] slot in vlan->taps[]:
- *     - if 'q' is NULL, return the first empty slot;
- *     - otherwise, return the slot this pointer occupies.
- */
-static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
-{
-       int i;
-
-       for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
-               if (rcu_dereference_protected(vlan->taps[i],
-                                             lockdep_is_held(&macvtap_lock)) == q)
-                       return i;
-       }
-
-       /* Should never happen */
-       BUG_ON(1);
-}
-
 static int macvtap_set_queue(struct net_device *dev, struct file *file,
                                struct macvtap_queue *q)
 {
        struct macvlan_dev *vlan = netdev_priv(dev);
-       int index;
        int err = -EBUSY;
 
        spin_lock(&macvtap_lock);
@@ -115,12 +96,12 @@ static int macvtap_set_queue(struct net_device *dev, struct file *file,
                goto out;
 
        err = 0;
-       index = get_slot(vlan, NULL);
        rcu_assign_pointer(q->vlan, vlan);
-       rcu_assign_pointer(vlan->taps[index], q);
+       rcu_assign_pointer(vlan->taps[vlan->numvtaps], q);
        sock_hold(&q->sk);
 
        q->file = file;
+       q->queue_index = vlan->numvtaps;
        file->private_data = q;
 
        vlan->numvtaps++;
@@ -140,15 +121,22 @@ out:
  */
 static void macvtap_put_queue(struct macvtap_queue *q)
 {
+       struct macvtap_queue *nq;
        struct macvlan_dev *vlan;
 
        spin_lock(&macvtap_lock);
        vlan = rcu_dereference_protected(q->vlan,
                                         lockdep_is_held(&macvtap_lock));
        if (vlan) {
-               int index = get_slot(vlan, q);
+               int index = q->queue_index;
+               BUG_ON(index >= vlan->numvtaps);
+
+               nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
+                                              lockdep_is_held(&macvtap_lock));
+               rcu_assign_pointer(vlan->taps[index], nq);
+               nq->queue_index = index;
 
-               RCU_INIT_POINTER(vlan->taps[index], NULL);
+               RCU_INIT_POINTER(vlan->taps[vlan->numvtaps - 1], NULL);
                RCU_INIT_POINTER(q->vlan, NULL);
                sock_put(&q->sk);
                --vlan->numvtaps;
@@ -182,8 +170,7 @@ static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
        rxq = skb_get_rxhash(skb);
        if (rxq) {
                tap = rcu_dereference(vlan->taps[rxq % numvtaps]);
-               if (tap)
-                       goto out;
+               goto out;
        }
 
        if (likely(skb_rx_queue_recorded(skb))) {
@@ -193,17 +180,10 @@ static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
                        rxq -= numvtaps;
 
                tap = rcu_dereference(vlan->taps[rxq]);
-               if (tap)
-                       goto out;
-       }
-
-       /* Everything failed - find first available queue */
-       for (rxq = 0; rxq < MAX_MACVTAP_QUEUES; rxq++) {
-               tap = rcu_dereference(vlan->taps[rxq]);
-               if (tap)
-                       break;
+               goto out;
        }
 
+       tap = rcu_dereference(vlan->taps[0]);
 out:
        return tap;
 }
@@ -219,19 +199,15 @@ static void macvtap_del_queues(struct net_device *dev)
        struct macvtap_queue *q, *qlist[MAX_MACVTAP_QUEUES];
        int i, j = 0;
 
-       /* macvtap_put_queue can free some slots, so go through all slots */
        spin_lock(&macvtap_lock);
-       for (i = 0; i < MAX_MACVTAP_QUEUES && vlan->numvtaps; i++) {
+       for (i = 0; i < vlan->numvtaps; i++) {
                q = rcu_dereference_protected(vlan->taps[i],
                                              lockdep_is_held(&macvtap_lock));
-               if (q) {
-                       qlist[j++] = q;
-                       RCU_INIT_POINTER(vlan->taps[i], NULL);
-                       RCU_INIT_POINTER(q->vlan, NULL);
-                       vlan->numvtaps--;
-               }
+               BUG_ON(q == NULL);
+               qlist[j++] = q;
+               RCU_INIT_POINTER(vlan->taps[i], NULL);
+               RCU_INIT_POINTER(q->vlan, NULL);
        }
-       BUG_ON(vlan->numvtaps != 0);
        /* guarantee that any future macvtap_set_queue will fail */
        vlan->numvtaps = MAX_MACVTAP_QUEUES;
        spin_unlock(&macvtap_lock);