linux-kernel - Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

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Message-ID: <CACGkMEtXWLicmszjkzOhX8Ta=LdGgsDahRUKDEVzBVG8am5vgg@mail.gmail.com>
Date: Thu, 16 Oct 2025 14:03:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Eugenio Perez Martin <eperezma@...hat.com>, Maxime Coquelin <mcoqueli@...hat.com>, 
	Yongji Xie <xieyongji@...edance.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Dragos Tatulea DE <dtatulea@...dia.com>
Subject: Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

On Thu, Oct 16, 2025 at 1:45 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Oct 16, 2025 at 01:39:58PM +0800, Jason Wang wrote:
> > > >
> > > > Not exactly bufferize, record.  E.g. we do not need to send
> > > > 100 messages to enable/disable promisc mode - together they
> > > > have no effect.
> >
> > Note that there's a case that multiple commands need to be sent, e.g
> > set rx mode. And assuming not all the commands are the best effort,
> > kernel VDUSE still needs to wait for the usersapce at least for a
> > while.
>
> Not wait, record. Generate 1st command, after userspace consumed it -
> generate and send second command and so on.

Right, that's what I asked in another thread, we still need a timeout
here. Then I think it would not be too much difference whether it is
VDUSE or CVQ that will fail or break the device. Conceptually, VDUSE
can only advertise NEEDS_RESET since it's a device implementation.
VDUSE can not simply break the device as it requires synchronization
which is not easy.

> But for each bit of data, at most one command has to be sent,
> we do not care if guest tweaked rx mode 3 times, we only care about
> the latest state.

Yes, but I want to know what's best when VDUSE meets userspace timeout.

Thanks

>
> --
> MST
>