Re: [Qemu-devel] Is IOThread for virtio-net a good idea?

[Jason Wang]

On 2019/2/12 上午11:55, Stefan Hajnoczi wrote:
> On Mon, Feb 11, 2019 at 09:52:01AM -0500, Michael S. Tsirkin wrote:
> > On Mon, Feb 11, 2019 at 04:40:44PM +0300, Anton Kuchin wrote:
> > > As far as I can see currently IOThread offloading is used only for block
> > > devices and all others are emulated by main thread.
> > >
> > > I expect that network devices can also benefit from processing in separate
> > > thread but I couldn't find any recent work in this direction. I'm going to
> > > implement a PoC but I want to ask if you know any previous attempts and do
> > > you know why it can be a total waste of time. Are there fundamental
> > > obstacles that prevent network emulation handling in IOThread?
> > No but vhost-net is there. Unlike block where you gain lots of
> > functionality such as snapshots there seems to be little to
> > be gained by doing it in userspace.
> Anthony Liguori tried virtio-net in a dedicated thread a long time ago
> but it was never completed/merged.
>
> I think the argument for vhost-net in the kernel is that userspace
> doesn't offer the same APIs as the kernel.  For example, is zero copy
> possible from userspace?


Actually, it will be simpler than doing it at kernel somehow. E.g 
technically, you can write a userspace NIC driver in qemu to achieve 
that or doing it through dpdk pmd.

Thanks


> Anton: If you want to do virtio-net in userspace, QEMU has
> vhost-user-net support so you can perform emulation in a separate
> process.
>
> Stefan