From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: tuntap: Overload handling
Date: Thu, 14 Feb 2013 08:32:27 -0800
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Cc: netdev@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>
To: Sebastian =?ISO-8859-1?Q?P=F6hn?= <sebastian.poehn@googlemail.com>
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On Thu, 2013-02-14 at 12:50 +0100, Sebastian P=C3=B6hn wrote:
> I am having a look on the tun driver to realize an userspace network
> driver ( TAP + UIO ). Maybe that's not the use-case tun is intended
> for.
>=20
> What I've noticed is that in tun.c Line 741
>=20
> static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_devic=
e *dev)
>=20
> /* Limit the number of packets queued by dividing txq length with the
>  * number of queues.
>  */
> if (skb_queue_len(&tfile->socket.sk->sk_receive_queue)
>  >=3D dev->tx_queue_len / tun->numqueues)
> goto drop;
>=20
> If a frame can not be tx it is dropped by the driver.
> Wouldn't it be more correct to netif_tx_stop_queue() so that packet
> drops are performed by the overlying traffic control code?
>=20
> Of course this is not very likely in virtual environments but as soon
> as any real network hop is involved it could be important.
>=20
> (I also had a look on some two year old version of tun.c. There
> queue/tx stopping was done correctly.)

You should ask Michael S. Tsirkin, as he removed the flow control
in commit 5d097109257c03a71845729f8db6b5770c4bbedc
(tun: only queue packets on device)