Migration of paused domains

Migration of paused domains

[Alessandro Sardo]

Hello,

today I wanted to find out if it was possible to migrate a paused 
domain. So, I tried the following:

# xm pause <dom>
# xm migrate <dom> <dest>

Unfortunately, the migration process would just hang before suspending 
the domain and transferring its state. In order to resume it and 
complete migration, I had to unpause the domain:

# xm unpause <dom>

After that, the process did get completed successfully.

-----

Then, I tried and track down the reason of this in the sources, and I 
came to the following snip (XendDomainInfo.py):

def waitForShutdown(self):
      self.state_updated.acquire()
           try:
                while self._stateGet() in 
(DOM_STATE_RUNNING,DOM_STATE_PAUSED):
                self.state_updated.wait()
           finally:
                self.state_updated.release()

It looks like that makes it wait forever, since the domain remains stuck 
in the DOM_STATE_PAUSED state.

Now, the question is: is that the right behaviour or am I missing 
something? Is it really not possible to migrate a paused domain?

Thanks,

- AS

RE: Migration of paused domains

[James Harper]

> today I wanted to find out if it was possible to migrate a paused
> domain. So, I tried the following:
> 
> # xm pause <dom>
> # xm migrate <dom> <dest>
> 

For PV domains, migrate requires the DomU itself to make a suspend call
to the hypervisor when it is ready to suspend. I guess it can't do that
if it is paused...

James

Re: Migration of paused domains

[Alessandro Sardo]

James Harper ha scritto:
>> today I wanted to find out if it was possible to migrate a paused
>> domain. So, I tried the following:
>>
>> # xm pause <dom>
>> # xm migrate <dom> <dest>
>>
> 
> For PV domains, migrate requires the DomU itself to make a suspend call
> to the hypervisor when it is ready to suspend. I guess it can't do that
> if it is paused...
> 
> James

I see. Would you be so kind to point me at that suspend call in the sources?

Thanks again!

- AS

Re: Migration of paused domains

[Mark Williamson]

On Saturday 19 July 2008, Alessandro Sardo wrote:
> James Harper ha scritto:
> >> today I wanted to find out if it was possible to migrate a paused
> >> domain. So, I tried the following:
> >>
> >> # xm pause <dom>
> >> # xm migrate <dom> <dest>
> >
> > For PV domains, migrate requires the DomU itself to make a suspend call
> > to the hypervisor when it is ready to suspend. I guess it can't do that
> > if it is paused...
> >
> > James
>
> I see. Would you be so kind to point me at that suspend call in the
> sources?

In the Linux sources I think you could start browsing from 
drivers/xen/core/reboot.c::xen_suspend().

The final hypercall to suspend the guest (HYPERVISOR_suspend) is done in 
drivers/xen/core/machine_reboot.c::take_machine_down()

Hope that helps,
Cheers,
Mark

>
> Thanks again!
>
> - AS
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel



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Migration of paused domains

[Rob Bradford]

I'm not sure if this is a real bug or not, but when attempting to test
my block device migration system I pause the domain to ensure that no
more writes to the backing block device will occur.

Unfortunately if the domain is pause an xm migrate command simply leads
to the xm migrate command hanging. I would have thought it should be
possible to migrate a paused domain. Is this a bug or is there a real
problem with trying to migrate a paused domain?

Cheers,

Rob
-- 
Rob Bradford <rob.bradford@xenoservers.net>

Re: Migration of paused domains

[Steven Hand]

> I'm not sure if this is a real bug or not, but when attempting to test
> my block device migration system I pause the domain to ensure that no
> more writes to the backing block device will occur.
> 
> Unfortunately if the domain is pause an xm migrate command simply leads
> to the xm migrate command hanging. I would have thought it should be
> possible to migrate a paused domain. Is this a bug or is there a real
> problem with trying to migrate a paused domain?

There is a problem in migrating (or saving) a paused paravirtual 
domain - the guest OS needs to be 'aware' that it is being suspended
so that it can ensure there are no stale mfns lying around (since 
these will no longer be valid after the resume / on the destination 
node). 


cheers,

S.

Re: Migration of paused domains

[Jayesh Salvi]

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There was a discussion on these lines sometime back.
http://lists.xensource.com/archives/html/xen-devel/2006-05/msg00521.html

On 8/3/06, Steven Hand <Steven.Hand@cl.cam.ac.uk> wrote:
>
>
> > I'm not sure if this is a real bug or not, but when attempting to test
> > my block device migration system I pause the domain to ensure that no
> > more writes to the backing block device will occur.
> >
> > Unfortunately if the domain is pause an xm migrate command simply leads
> > to the xm migrate command hanging. I would have thought it should be
> > possible to migrate a paused domain. Is this a bug or is there a real
> > problem with trying to migrate a paused domain?
>
> There is a problem in migrating (or saving) a paused paravirtual
> domain - the guest OS needs to be 'aware' that it is being suspended
> so that it can ensure there are no stale mfns lying around (since
> these will no longer be valid after the resume / on the destination
> node).
>
>
> cheers,
>
> S.
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>



-- 
Jayesh
------------------------------------------------------------------------
Everything you can imagine is real

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