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Date: Thu, 23 May 2013 14:41:09 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [net-next RFC 5/8] macvtap: eliminate linear search
On Thu, May 23, 2013 at 11:12:30AM +0800, Jason Wang wrote:
> 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@...hat.com>
> ---
> drivers/net/macvtap.c | 63 +++++++++++++++---------------------------------
> 1 files changed, 20 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index a36e49e..5fd341c 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++;
> @@ -140,16 +121,23 @@ 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);
>
> - RCU_INIT_POINTER(vlan->taps[index], NULL);
> + rcu_assign_pointer(vlan->taps[index],
> + vlan->taps[vlan->numvtaps - 1]);
> RCU_INIT_POINTER(q->vlan, NULL);
> + nq = rcu_dereference_protected(vlan->taps[index],
> + lockdep_is_held(&macvtap_lock));
> + nq->queue_index = index;
> +
> sock_put(&q->sk);
Hmm this looks like a bug BTW: sock_put should be after
no one uses this tap, so must be after synchronize_rcu.
No?
> --vlan->numvtaps;
> }
So:
nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
lockdep_is_held(&macvtap_lock));
rcu_assign_pointer(vlan->taps[index], nq);
same thing?
> @@ -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;
> }
> @@ -221,17 +201,14 @@ static void macvtap_del_queues(struct net_device *dev)
>
> /* 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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