linux-kernel - [PATCH net-next v7 9/9] tun/tap & vhost-net: avoid ptr

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Message-ID: <2e4e2944-832a-47e1-bdf9-32c636bcb6bf@tu-dortmund.de>
Date: Mon, 12 Jan 2026 12:28:37 +0100
From: Simon Schippers <simon.schippers@...dortmund.de>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, willemdebruijn.kernel@...il.com,
        andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, eperezma@...hat.com,
        leiyang@...hat.com, stephen@...workplumber.org, jon@...anix.com,
        tim.gebauer@...dortmund.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux.dev
Subject: [PATCH net-next v7 9/9] tun/tap & vhost-net: avoid ptr_ring tail-drop
 when qdisc is present

On 1/12/26 12:19, Michael S. Tsirkin wrote:
> On Mon, Jan 12, 2026 at 12:17:12PM +0100, Simon Schippers wrote:
>> On 1/12/26 05:33, Michael S. Tsirkin wrote:
>>> On Fri, Jan 09, 2026 at 11:14:54AM +0100, Simon Schippers wrote:
>>>> Am I not allowed to stop the queue and then return NETDEV_TX_BUSY?
>>>
>>> We jump through a lot of hoops in virtio_net to avoid using
>>> NETDEV_TX_BUSY because that bypasses all the net/ cleverness.
>>> Given your patches aim to improve precisely ring full,
>>> I would say stopping proactively before NETDEV_TX_BUSY
>>> should be a priority.
>>>
>>
>> I already proactively stop here with the approach you proposed in
>> the v6.
>> Or am I missing something (apart from the xdp path)?
> 
> Yes, I am just answering the general question you posed.

Ah okay.

> 
>>
>> And yes I also dislike returning NETDEV_TX_BUSY but I do not see how
>> this can be prevented with lltx enabled.
> 
> Preventing NETDEV_TX_BUSY 100% of the time is not required. It's there
> to handle races.

Great to know. Thanks