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authorMichael S. Tsirkin <mst@redhat.com>2012-12-03 10:07:14 +0000
committerDavid S. Miller <davem@davemloft.net>2012-12-03 15:07:36 -0500
commit5d097109257c03a71845729f8db6b5770c4bbedc (patch)
tree4ef14ea47b21f6f81412c95889ca30147e0f0458 /drivers/net
parent9ba2add3cf5c103b7236f82a023c8ee05a51e4d1 (diff)
tun: only queue packets on device
Historically tun supported two modes of operation: - in default mode, a small number of packets would get queued at the device, the rest would be queued in qdisc - in one queue mode, all packets would get queued at the device This might have made sense up to a point where we made the queue depth for both modes the same and set it to a huge value (500) so unless the consumer is stuck the chance of losing packets is small. Thus in practice both modes behave the same, but the default mode has some problems: - if packets are never consumed, fragments are never orphaned which cases a DOS for sender using zero copy transmit - overrun errors are hard to diagnose: fifo error is incremented only once so you can not distinguish between userspace that is stuck and a transient failure, tcpdump on the device does not show any traffic Userspace solves this simply by enabling IFF_ONE_QUEUE but there seems to be little point in not doing the right thing for everyone, by default. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net')
-rw-r--r--drivers/net/tun.c24
1 files changed, 8 insertions, 16 deletions
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 71f6874d804..a1b2389e6d7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -690,21 +690,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
* number of queues.
*/
if (skb_queue_len(&tfile->socket.sk->sk_receive_queue)
- >= dev->tx_queue_len / tun->numqueues){
- if (!(tun->flags & TUN_ONE_QUEUE)) {
- /* Normal queueing mode. */
- /* Packet scheduler handles dropping of further packets. */
- netif_stop_subqueue(dev, txq);
-
- /* We won't see all dropped packets individually, so overrun
- * error is more appropriate. */
- dev->stats.tx_fifo_errors++;
- } else {
- /* Single queue mode.
- * Driver handles dropping of all packets itself. */
- goto drop;
- }
- }
+ >= dev->tx_queue_len / tun->numqueues)
+ goto drop;
/* Orphan the skb - required as we might hang on to it
* for indefinite time. */
@@ -1319,7 +1306,6 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
schedule();
continue;
}
- netif_wake_subqueue(tun->dev, tfile->queue_index);
ret = tun_put_user(tun, tfile, skb, iv, len);
kfree_skb(skb);
@@ -1482,6 +1468,9 @@ static int tun_flags(struct tun_struct *tun)
if (tun->flags & TUN_NO_PI)
flags |= IFF_NO_PI;
+ /* This flag has no real effect. We track the value for backwards
+ * compatibility.
+ */
if (tun->flags & TUN_ONE_QUEUE)
flags |= IFF_ONE_QUEUE;
@@ -1632,6 +1621,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
else
tun->flags &= ~TUN_NO_PI;
+ /* This flag has no real effect. We track the value for backwards
+ * compatibility.
+ */
if (ifr->ifr_flags & IFF_ONE_QUEUE)
tun->flags |= TUN_ONE_QUEUE;
else