netdev - Re: [PATCH net-next v7 7/9] vhost-net: vhost-net: replace rx

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Message-ID: <CACGkMEsC0-d4oS54BHNdFVKS+74P7SdnNHPHe_d0pmo-_86ipg@mail.gmail.com>
Date: Mon, 12 Jan 2026 10:54:15 +0800
From: Jason Wang <jasowang@...hat.com>
To: Simon Schippers <simon.schippers@...dortmund.de>
Cc: willemdebruijn.kernel@...il.com, andrew+netdev@...n.ch, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	mst@...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: Re: [PATCH net-next v7 7/9] vhost-net: vhost-net: replace rx_ring
 with tun/tap ring wrappers

On Fri, Jan 9, 2026 at 5:57 PM Simon Schippers
<simon.schippers@...dortmund.de> wrote:
>
> On 1/9/26 07:04, Jason Wang wrote:
> > On Thu, Jan 8, 2026 at 3:48 PM Simon Schippers
> > <simon.schippers@...dortmund.de> wrote:
> >>
> >> On 1/8/26 05:38, Jason Wang wrote:
> >>> On Thu, Jan 8, 2026 at 5:06 AM Simon Schippers
> >>> <simon.schippers@...dortmund.de> wrote:
> >>>>
> >>>> Replace the direct use of ptr_ring in the vhost-net virtqueue with
> >>>> tun/tap ring wrapper helpers. Instead of storing an rx_ring pointer,
> >>>> the virtqueue now stores the interface type (IF_TUN, IF_TAP, or IF_NONE)
> >>>> and dispatches to the corresponding tun/tap helpers for ring
> >>>> produce, consume, and unconsume operations.
> >>>>
> >>>> Routing ring operations through the tun/tap helpers enables netdev
> >>>> queue wakeups, which are required for upcoming netdev queue flow
> >>>> control support shared by tun/tap and vhost-net.
> >>>>
> >>>> No functional change is intended beyond switching to the wrapper
> >>>> helpers.
> >>>>
> >>>> Co-developed-by: Tim Gebauer <tim.gebauer@...dortmund.de>
> >>>> Signed-off-by: Tim Gebauer <tim.gebauer@...dortmund.de>
> >>>> Co-developed by: Jon Kohler <jon@...anix.com>
> >>>> Signed-off-by: Jon Kohler <jon@...anix.com>
> >>>> Signed-off-by: Simon Schippers <simon.schippers@...dortmund.de>
> >>>> ---
> >>>>  drivers/vhost/net.c | 92 +++++++++++++++++++++++++++++----------------
> >>>>  1 file changed, 60 insertions(+), 32 deletions(-)
> >>>>
> >>>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> >>>> index 7f886d3dba7d..215556f7cd40 100644
> >>>> --- a/drivers/vhost/net.c
> >>>> +++ b/drivers/vhost/net.c
> >>>> @@ -90,6 +90,12 @@ enum {
> >>>>         VHOST_NET_VQ_MAX = 2,
> >>>>  };
> >>>>
> >>>> +enum if_type {
> >>>> +       IF_NONE = 0,
> >>>> +       IF_TUN = 1,
> >>>> +       IF_TAP = 2,
> >>>> +};
> >>>
> >>> This looks not elegant, can we simply export objects we want to use to
> >>> vhost like get_tap_socket()?
> >>
> >> No, we cannot do that. We would need access to both the ptr_ring and the
> >> net_device. However, the net_device is protected by an RCU lock.
> >>
> >> That is why {tun,tap}_ring_consume_batched() are used:
> >> they take the appropriate locks and handle waking the queue.
> >
> > How about introducing a callback in the ptr_ring itself, so vhost_net
> > only need to know about the ptr_ring?
>
> That would be great, but I'm not sure whether this should be the
> responsibility of the ptr_ring.
>
> If the ptr_ring were to keep track of the netdev queue, it could handle
> all the management itself - stopping the queue when full and waking it
> again once space becomes available.
>
> What would be your idea for implementing this?

During ptr_ring_init() register a callback, the callback will be
trigger during ptr_ring_consume() or ptr_ring_consume_batched() when
ptr_ring find there's a space for ptr_ring_produce().

Thanks

>
> >
> > Thanks
> >
> >>
> >>>
> >>> Thanks
> >>>
> >>
> >
>