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Subject[net-next PATCH 6/8] macvtap: eliminate linear search
Date
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>
---
drivers/net/macvtap.c | 64 +++++++++++++++---------------------------------
1 files changed, 20 insertions(+), 44 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index d18130b..5ccba99 100644
--- 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);
--
1.7.1


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