Linux Virtualization - Mar 2016 - [RFC qemu 0/4] A PV solution for live migration optimization

> > This patch set is the QEMU side implementation.
> >
> > The virtio-balloon is extended so that QEMU can get the free pages
> > information from the guest through virtio.
> >
> > After getting the free pages information (a bitmap), QEMU can use it
> > to filter out the guest's free pages in the ram bulk stage. This
make
> > the live migration process much more efficient.
> >
> > This RFC version doesn't take the post-copy and RDMA into
> > consideration, maybe both of them can benefit from this PV solution by
> > with some extra modifications.
> 
> I like the idea, just have to prove (review) and test it a lot to ensure we
don't
> end up skipping pages that matter.
> 
> However, there are a couple of points:
> 
> In my opinion, the information that's exchanged between the guest and
the
> host should be exchanged over a virtio-serial channel rather than virtio-
> balloon.  First, there's nothing related to the balloon here.
> It just happens to be memory info.  Second, I would never enable balloon in
> a guest that I want to be performance-sensitive.  So even if you add this
as
> part of balloon, you'll find no one is using this solution.
> 
> Secondly, I suggest virtio-serial, because it's meant exactly to
exchange free-
> flowing information between a host and a guest, and you don't need to
> extend any part of the protocol for it (hence no changes necessary to the
> spec).  You can see how spice, vnc, etc., use virtio-serial to exchange
data.
> 
> 
> 		Amit
Hi Amit,

 Could provide more information on how to use virtio-serial to exchange data? 
Thread , Wiki or code are all OK.
 I have not find some useful information yet.

Thanks
Liang

On (Thu) 10 Mar 2016 [07:44:19], Li, Liang Z wrote:
> 
> Hi Amit,
> 
>  Could provide more information on how to use virtio-serial to exchange
data?  Thread , Wiki or code are all OK.
>  I have not find some useful information yet.
See this commit in the Linux sources:

108fc82596e3b66b819df9d28c1ebbc9ab5de14c

that adds a way to send guest trace data over to the host.  I think
that's the most relevant to your use-case.  However, you'll have to
add an in-kernel user of virtio-serial (like the virtio-console code
-- the code that deals with tty and hvc currently).  There's no other
non-tty user right now, and this is the right kind of use-case to add
one for!

For many other (userspace) use-cases, see the qemu-guest-agent in the
qemu sources.

The API is documented in the wiki:

http://www.linux-kvm.org/page/Virtio-serial_API

and the feature pages have some information that may help as well:

https://fedoraproject.org/wiki/Features/VirtioSerial

There are some links in here too:

http://log.amitshah.net/2010/09/communication-between-guests-and-hosts/

Hope this helps.


		Amit

> >  Could provide more information on how to use virtio-serial to
exchange
> data?  Thread , Wiki or code are all OK.
> >  I have not find some useful information yet.
> 
> See this commit in the Linux sources:
> 
> 108fc82596e3b66b819df9d28c1ebbc9ab5de14c
> 
> that adds a way to send guest trace data over to the host.  I think
that's the
> most relevant to your use-case.  However, you'll have to add an
in-kernel
> user of virtio-serial (like the virtio-console code
> -- the code that deals with tty and hvc currently).  There's no other
non-tty
> user right now, and this is the right kind of use-case to add one for!
> 
> For many other (userspace) use-cases, see the qemu-guest-agent in the
> qemu sources.
> 
> The API is documented in the wiki:
> 
> http://www.linux-kvm.org/page/Virtio-serial_API
> 
> and the feature pages have some information that may help as well:
> 
> https://fedoraproject.org/wiki/Features/VirtioSerial
> 
> There are some links in here too:
> 
> http://log.amitshah.net/2010/09/communication-between-guests-and-
> hosts/
> 
> Hope this helps.
> 
> 
> 		Amit
Thanks a lot !!

Liang