Jason Wang <jasow...@redhat.com> writes: > On 2019/4/10 下午9:01, David Woodhouse wrote: >> On Wed, 2019-04-10 at 15:01 +0300, David Woodhouse wrote: >>> --- a/drivers/net/tun.c >>> +++ b/drivers/net/tun.c >>> @@ -1125,7 +1128,9 @@ static netdev_tx_t tun_net_xmit(struct sk_buff >>> *skb, struct net_device *dev) >>> if (tfile->flags & TUN_FASYNC) >>> kill_fasync(&tfile->fasync, SIGIO, POLL_IN); >>> tfile->socket.sk->sk_data_ready(tfile->socket.sk); >>> >>> + if (!ptr_ring_empty(&tfile->tx_ring)) >>> + netif_stop_queue(tun->dev); >>> rcu_read_unlock(); >>> return NETDEV_TX_OK; >>> >>> >> Hm, that should be using ptr_ring_full() shouldn't it? So... >> >> --- a/drivers/net/tun.c >> +++ b/drivers/net/tun.c >> @@ -1121,6 +1121,9 @@ static netdev_tx_t tun_net_xmit(struct s >> if (ptr_ring_produce(&tfile->tx_ring, skb)) >> goto drop; >> >> + if (ptr_ring_full(&tfile->tx_ring)) >> + netif_stop_queue(tun->dev); >> + >> /* Notify and wake up reader process */ >> if (tfile->flags & TUN_FASYNC) >> kill_fasync(&tfile->fasync, SIGIO, POLL_IN); >> @@ -2229,6 +2232,7 @@ static ssize_t tun_do_read(struct tun_st >> consume_skb(skb); >> } >> >> + netif_wake_queue(tun->dev); >> return ret; >> } >> >> >> That doesn't seem to make much difference at all; it's still dropping a >> lot of packets because ptr_ring_produce() is returning non-zero. > > > I think you need try to stop the queue just in this case? Ideally we may > want to stop the queue when the queue is about to full, but we don't > have such helper currently.
Ideally we want to react when the queue starts building rather than when it starts getting full; by pushing back on upper layers (or, if forwarding, dropping packets to signal congestion). In practice, this means tuning the TX ring to the *minimum* size it can be without starving (this is basically what BQL does for Ethernet), and keeping packets queued in the qdisc layer instead, where it can be managed... -Toke
