Re: Migration - Xen 4.3

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

On Tue, 20 Jan 2015, Jean-Yves Migeon wrote:
> > I have never got migration to succeed, nor suspend/resume (which is
> > fundamentally the same operation). Sometimes suspend appears to work,
> > but resume fails.
> >
> > The usual symptoms for me are that the domain just continues
> > regardless (i.e. it ignores the suspend request) rather than it locks.
> > However, from a dom0 point of view, it waits for confirmation of
> > suspension and so blocks any further operations on it.
> >
> > I understand that the problem is reasonably well understood by the
> > relevant developers, but that debugging is hard.
>
> Now that's a regression, suspend is supposed to finish correctly (e.g. the 
> domain is descheduled and you get a core file that represents VM's state). 
> Resuming is the culprit and I failed to get $SPARETIME to investigate the 
> situation in the last few months; usual symptoms is a corrupted Xen I/O ring 
> that completely thrashes xbdback(4) and leads to a paniced domU (or a very, 
> very slow dom0 like an interrupt storm).
>
> Do you try suspend/resume on UP or MP domU?

OK, I tried again with latest -current/amd64 and suspend/resume did 
superficially work. Suspend was fine and it appeared to resume. du / 
was able to go through the whole FS, but networking was dead.
Also, I could not cleanly shut it down.

I tried again and then hit the xbd deadlock which panicked:
iostat_isbusy() at netbsd:iostat_isbusy
xbd_handler() at netbsd:xbd_handler+0x192

Out of interest, I tried migrating between two homogeneous hosts with the 
same results.

So no regression, but no progress, as expected.

> Using xl or xm?

I'm using XenServer, so xapi rather than xl/xm.

--
Stephen