Re: [Qemu-devel] [RFC 0/2] virtio-vhost-user: add virtio-vhost-user device

[Wei Wang <wei.w.wang@intel.com>]

On 01/22/2018 08:17 PM, Stefan Hajnoczi wrote:
> On Mon, Jan 22, 2018 at 11:33:46AM +0800, Jason Wang wrote:
>> On 2018年01月19日 21:06, Stefan Hajnoczi wrote:
>>
>> Probably not for the following cases:
>>
>> 1) kick/call
> I disagree here because kick/call is actually very efficient!
>
> VM1's irqfd is the ioeventfd for VM2.  When VM2 writes to the ioeventfd
> there is a single lightweight vmexit which injects an interrupt into
> VM1.  QEMU is not involved and the host kernel scheduler is not involved
> so this is a low-latency operation.
>
> I haven't tested this yet but the ioeventfd code looks like this will
> work.


This have been tested in vhost-pci v2 patches which worked with with a 
kernel driver. It worked pretty well.

>> Btw, it's better to have some early numbers, e.g what testpmd reports during
>> forwarding.
> I need to rely on others to do this (and many other things!) because
> virtio-vhost-user isn't the focus of my work.
>
> These patches were written to demonstrate my suggestions for vhost-pci.
> They were written at work but also on weekends, early mornings, and late
> nights to avoid delaying Wei and Zhiyong's vhost-pci work too much.
>
> If this approach has merit then I hope others will take over and I'll
> play a smaller role addressing some of the todo items and cleanups.

Thanks again for the great effort, your implementation looks nice.

If we finally decide to go with the virtio-vhost-user approach, I think 
zhiyong and I can help take over the work to continue, too.

I'm still thinking about solutions to the two issues that I shared 
yesterday - it should be like a normal PCI device, and if we unbind its 
driver, and bind back, it should also work.


Best,
Wei