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Thanks

On Mon, Feb 2, 2015 at 4:09 AM, Daniel P. Berrange <berrange at redhat.com>
wrote:

> On Sun, Feb 01, 2015 at 03:03:45PM -0700, David Medberry wrote:
> > I'll second much of what Rob said:
> > API that indicated how many live-migrations (l-m) were going would be
> good.
> > API that told you what progress (and start time) a given l-m had made
> would
> > be great.
> > API to cancel a given l-m would also be great. I think this is a
> preferred
> > approach over an auto timeout (it would give us the tools we need to
> > implement an auto timeout though.)
> >
> > I like the idea of trying auto-convergence (and agree it should be flavor
> > feature and likely not the default.) I suspect this one needs some
> testing.
> > It may be fine to automatically do this if it doesn't actually throttle
> the
> > VM some 90-99% of the time.  (Presumably this could also increase the max
> > downtime between cutover as well as throttling the vm.)
>
> For reference the auto-convergance code in QEMU is this commit
>
>
> http://git.qemu.org/?p=qemu.git;a=commit;h=7ca1dfad952d8a8655b32e78623edcc38a51b14a
>
> If the migration operation is making good progress, it does not have any
> impact on the guest. Periodically it checks the data transfer progress and
> if the guest has dirtied more than 50% of the pages than were transferred
> it'll start throttling. It throttles by simplying preventing the guest
> vCPUs from running for a period of time. So the guest will obviously get
> a performance drop, but the migration is more likely (but not guaranteed)
> to succeed.
>
> From the QEMU level you can actually enable this on the fly it seems, but
> libvirt only lets it be set at startup of migration.
>
> Regards,
> Daniel
> --
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