Re: [Qemu-devel] vhost-pci and virtio-vhost-user

[Stefan Hajnoczi]

On Mon, Jan 15, 2018 at 02:56:31PM +0800, Jason Wang wrote:
> On 2018年01月12日 18:18, Stefan Hajnoczi wrote:
> > > And what's more important, according to the kvm 2016 slides of vhost-pci,
> > > the motivation of vhost-pci is not building SDN but a chain of VNFs. So
> > > bypassing the central vswitch through a private VM2VM path does make 
> > > sense.
> > > (Though whether or not vhost-pci is the best choice is still 
> > > questionable).
> > This is probably my fault.  Maybe my networking terminology is wrong.  I
> > consider "virtual network functions" to be part of "software-defined
> > networking" use cases.  I'm not implying there must be a central virtual
> > switch.
> > 
> > To rephrase: vhost-pci enables exitless VM2VM communication.
> 
> The problem is, exitless is not what vhost-pci invents, it could be achieved
> now when both sides are doing busypolling.

The only way I'm aware of is ivshmem.  But ivshmem lacks a family of
standard device types that allows different implementations to
interoperate.  We already have the virtio family of device types, so it
makes sense to work on a virtio-based solution.

Perhaps I've missed a different approach for exitless VM2VM
communication.  Please explain how VM1 and VM2 can do exitless network
communication today?

Also, how can VM1 provide SCSI I/O services to VM2 today?

Stefan

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