linux-kernel - [PATCH net-next v6 0/8] tun/tap & vhost-net: netdev queue flow control to avoid ptr

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Message-ID: <2bc56d3e-f4da-41d5-ab63-29c63525eb30@tu-dortmund.de>
Date: Wed, 26 Nov 2025 10:24:42 +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,
        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 v6 0/8] tun/tap & vhost-net: netdev queue flow
 control to avoid ptr_ring tail drop

On 11/26/25 08:15, Michael S. Tsirkin wrote:
> On Fri, Nov 21, 2025 at 10:22:54AM +0100, Simon Schippers wrote:
>> I agree, but I really would like to reduce the buffer bloat caused by the
>> default 500 TUN / 1000 TAP packet queue without losing performance.
> 
> that default is part of the userspace API and can't be changed.
> just change whatever userspace is creating your device.
> 

Yes, but I’m thinking about introducing a new interface flag like
IFF_BQL. However, as noted earlier, there are significant implementation
challenges.

I think there can be advantages to something like VPN's on mobile
devices where the throughput varies between a few Mbit/s (small TUN/TAP
queue is fine) and multiple Gbit/s (need a bigger queue).