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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] Is IOThread for virtio-net a good idea?
Date: Tue, 12 Feb 2019 11:55:05 +0800
User-agent: Mutt/1.10.1 (2018-07-13)

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?

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


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