Re: [Qemu-devel] Towards an ivshmem 2.0?

[Wang, Wei W]

On Sunday, January 29, 2017 10:14 PM, Jan Kiszka wrote:
> On 2017-01-29 15:00, Marc-André Lureau wrote:
> > Hi
> >
> > On Sun, Jan 29, 2017 at 12:44 PM Jan Kiszka <address@hidden
> > <mailto:address@hidden>> wrote:
> >
> >     >> Of course, I'm careful with investing much time into expanding the
> >     >> existing, for Jailhouse possibly sufficient design if there no real
> >     >> interest in continuing the ivshmem support in QEMU - because of
> >     >> vhost-pci or other reasons. But if that interest exists, it would be
> >     >> beneficial for us to have QEMU supporting a compatible version
> >     and using
> >     >> the same guest drivers. Then I would start looking into concrete
> >     patches
> >     >> for it as well.
> >     >
> >     > Interest is difficult for me to gauge, not least because alternatives
> >     > are still being worked on.
> >
> >     I'm considering to suggest this as GSoC project now.
> >
> >
> > It's better for a student and for the community if the work get
> > accepted in the end.
> >
> > So, I think that could be an intersting GSoC (implementing your
> > ivshmem
> > 2 proposal). However, if the qemu community isn't ready to accept a
> > new ivshmem, and would rather have vhost-pci based solution, I would
> > suggest a different project (hopefully Wei Wang can help define it and 
> > mentor):
> > work on a vhost-pci using dedicated shared PCI BARs (and kernel
> > support to avoid extra copy - if I understand the extra copy situation 
> > correctly).

Thanks for the suggestion. I’m glad to help it. 

For that sort of usage (static configuration extension [1]), I’m thinking that 
it’s possible to build symmetric vhost-pci-net communication, as appose to 
“vhost-pci-net<-> virtio-net”.

> It's still open if vhost-pci can replace ivshmem (not to speak of being 
> desirable
> for Jailhouse - I'm still studying). In that light, having both 
> implementations
> available to do real comparisons is valuable IMHO.
> 
> That said, we will play with open cards, explain the student the situation 
> and let
> her/him decide knowingly.
 
I think the static configuration of vhost-pci would be quite similar to your 
ivshmem based proposal- could be thought of as moving your proposal to the 
virtio device structure. Do you see any more big difference? Or is there any 
fundamental reason that it is not good to do that based on virtio? Thanks.

Best,
Wei

[1] static configuration extension: set the vhost-pci device via the QEMU 
command line (rather than hotplugging via vhost-user protocol) , and  share a 
piece of memory between two VMs (rather than the whole VM's memory)