[Qemu-devel] Qemu only uses a Qemu File to communicate in two hosts?

[Qemu-devel] Qemu only uses a Qemu File to communicate in two hosts?

[Gary Jordan]

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Hi,
Does Qemu only use the QEMUFile to load the state of VM after migration?
Is there a way for two vm guests to communicate like two threads or
processes?

Gary

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Re: [Qemu-devel] Qemu only uses a Qemu File to communicate in two hosts?

[Eric Blake]

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On 06/30/2014 03:02 PM, Gary Jordan wrote:
> Hi,
> Does Qemu only use the QEMUFile to load the state of VM after migration?

Normally, yes.  Migration must work as a one-way protocol in the common
case when used with default options.

There is a migration mode that uses RDMA which requires bi-directional
communication in order to speed up aspects of memory migration.  But
this mode is transparent to the guest, and requires you to take extra
steps at both source and destination (along with having an infiniband
connection capable of RDMA communication between the two hosts).

> Is there a way for two vm guests to communicate like two threads or
> processes?

If there is, it has nothing to do with migration.  It sounds like you
are asking about ivshmem and/or virtio; if so, search the archives for
recent discussions on the topic.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] Qemu only uses a Qemu File to communicate in two hosts?

[Gary Jordan]

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Hi Eric,

Could I find a way for two guests in two hosts to communicate?   Like qemu
starts one vm in Host 1 and qemu also starts a vm in Host 2, the vm can
share their memory.  Is there some existed way to do that, like remote IPC
in qemu?

Thanks for your reply.

---Gary


2014-06-30 17:08 GMT-04:00 Eric Blake <eblake@redhat.com>:

> On 06/30/2014 03:02 PM, Gary Jordan wrote:
> > Hi,
> > Does Qemu only use the QEMUFile to load the state of VM after migration?
>
> Normally, yes.  Migration must work as a one-way protocol in the common
> case when used with default options.
>
> There is a migration mode that uses RDMA which requires bi-directional
> communication in order to speed up aspects of memory migration.  But
> this mode is transparent to the guest, and requires you to take extra
> steps at both source and destination (along with having an infiniband
> connection capable of RDMA communication between the two hosts).
>
> > Is there a way for two vm guests to communicate like two threads or
> > processes?
>
> If there is, it has nothing to do with migration.  It sounds like you
> are asking about ivshmem and/or virtio; if so, search the archives for
> recent discussions on the topic.
>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>

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Re: [Qemu-devel] Qemu only uses a Qemu File to communicate in two hosts?

[Eric Blake]

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On 06/30/2014 03:58 PM, Gary Jordan wrote:
> Hi Eric,

[please don't top-post in technical lists]

> 
> Could I find a way for two guests in two hosts to communicate?   Like qemu
> starts one vm in Host 1 and qemu also starts a vm in Host 2, the vm can
> share their memory.  Is there some existed way to do that, like remote IPC
> in qemu?

How would you communicate between two bare-metal hosts?  Emulate that
same setup in your two guests.

You appear to be intent on setting up shared memory solutions, when I
think the better thing is to focus on setting up efficient emulated
network device solutions.  Then your code will be portable no matter how
the network device frontend is hooked up to the host backend (and it may
be possible to have a host backend that uses shared memory for a very
efficient network device emulation when two VMs are on the same host,
but which can also be ported to work between VMs on different hosts by
using regular networking - and that's what virtio-net is focusing on
defining).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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