On Thu, Mar 12, 2026 at 02:06:37PM +0100, Simon Schippers wrote: > Add tun_wake_queue() to tun.c and export it for use by vhost-net. The > function validates that the file belongs to a tun/tap device, > dereferences the tun_struct under RCU, and delegates to > __tun_wake_queue(). > > vhost_net_buf_produce() now calls tun_wake_queue() after a successful > batched consume of the ring to allow the netdev subqueue to be woken up.
A sentence missing here: the point is to allow queue to be stopped when it gets full, which is required for traffic shaping - implemented by the following "avoid ptr_ring tail-drop when a qdisc is present" > Without the corresponding queue stopping (introduced in a subsequent > commit), this patch alone causes a slight throughput regression for a > tap+vhost-net setup sending to a qemu VM: > 3.948 Mpps to 3.888 Mpps (-1.5%). > > Details: AMD Ryzen 5 5600X at 4.3 GHz, 3200 MHz RAM, isolated QEMU > threads, XDP drop program active in VM, pktgen sender; Avg over > 20 runs @ 100,000,000 packets. SRSO and spectre v2 mitigations disabled. > > Co-developed-by: Tim Gebauer <[email protected]> > Signed-off-by: Tim Gebauer <[email protected]> > Signed-off-by: Simon Schippers <[email protected]> > --- > drivers/net/tun.c | 21 +++++++++++++++++++++ > drivers/vhost/net.c | 15 +++++++++++---- > include/linux/if_tun.h | 3 +++ > 3 files changed, 35 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index a82d665dab5f..b86582cc6cb6 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -3760,6 +3760,27 @@ struct ptr_ring *tun_get_tx_ring(struct file *file) > } > EXPORT_SYMBOL_GPL(tun_get_tx_ring); > > +void tun_wake_queue(struct file *file) > +{ > + struct tun_file *tfile; > + struct tun_struct *tun; > + > + if (file->f_op != &tun_fops) > + return; > + tfile = file->private_data; > + if (!tfile) > + return; > + > + rcu_read_lock(); > + > + tun = rcu_dereference(tfile->tun); > + if (tun) > + __tun_wake_queue(tun, tfile); > + > + rcu_read_unlock(); > +} > +EXPORT_SYMBOL_GPL(tun_wake_queue); > + > module_init(tun_init); > module_exit(tun_cleanup); > MODULE_DESCRIPTION(DRV_DESCRIPTION); > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 80965181920c..c8ef804ef28c 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -176,13 +176,19 @@ static void *vhost_net_buf_consume(struct vhost_net_buf > *rxq) > return ret; > } > > -static int vhost_net_buf_produce(struct vhost_net_virtqueue *nvq) > +static int vhost_net_buf_produce(struct sock *sk, > + struct vhost_net_virtqueue *nvq) > { > + struct file *file = sk->sk_socket->file; > struct vhost_net_buf *rxq = &nvq->rxq; > > rxq->head = 0; > rxq->tail = ptr_ring_consume_batched(nvq->rx_ring, rxq->queue, > VHOST_NET_BATCH); > + > + if (rxq->tail) > + tun_wake_queue(file); > + > return rxq->tail; > } > > @@ -209,14 +215,15 @@ static int vhost_net_buf_peek_len(void *ptr) > return __skb_array_len_with_tag(ptr); > } > > -static int vhost_net_buf_peek(struct vhost_net_virtqueue *nvq) > +static int vhost_net_buf_peek(struct sock *sk, > + struct vhost_net_virtqueue *nvq) > { > struct vhost_net_buf *rxq = &nvq->rxq; > > if (!vhost_net_buf_is_empty(rxq)) > goto out; > > - if (!vhost_net_buf_produce(nvq)) > + if (!vhost_net_buf_produce(sk, nvq)) > return 0; > > out: > @@ -995,7 +1002,7 @@ static int peek_head_len(struct vhost_net_virtqueue > *rvq, struct sock *sk) > unsigned long flags; > > if (rvq->rx_ring) > - return vhost_net_buf_peek(rvq); > + return vhost_net_buf_peek(sk, rvq); > > spin_lock_irqsave(&sk->sk_receive_queue.lock, flags); > head = skb_peek(&sk->sk_receive_queue); > diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h > index 80166eb62f41..ab3b4ebca059 100644 > --- a/include/linux/if_tun.h > +++ b/include/linux/if_tun.h > @@ -22,6 +22,7 @@ struct tun_msg_ctl { > #if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE) > struct socket *tun_get_socket(struct file *); > struct ptr_ring *tun_get_tx_ring(struct file *file); > +void tun_wake_queue(struct file *file); > > static inline bool tun_is_xdp_frame(void *ptr) > { > @@ -55,6 +56,8 @@ static inline struct ptr_ring *tun_get_tx_ring(struct file > *f) > return ERR_PTR(-EINVAL); > } > > +static inline void tun_wake_queue(struct file *f) {} > + > static inline bool tun_is_xdp_frame(void *ptr) > { > return false; > -- > 2.43.0
