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Re: [Qemu-devel] KVM call agenda for Tuesday, June 19th

From: Dor Laor
Subject: Re: [Qemu-devel] KVM call agenda for Tuesday, June 19th
Date: Wed, 11 Jul 2012 13:01:15 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1

On 06/19/2012 08:22 PM, Michael Roth wrote:
On Tue, Jun 19, 2012 at 11:34:42PM +0900, Takuya Yoshikawa wrote:
On Tue, 19 Jun 2012 09:01:36 -0500
Anthony Liguori <address@hidden> wrote:

I'm not at all convinced that postcopy is a good idea.  There needs a clear
expression of what the value proposition is that's backed by benchmarks.  Those
benchmarks need to include latency measurements of downtime which so far, I've
not seen.

I don't want to take any postcopy patches until this discussion happens.


I rather see postcopy as a way of migrating guests forcibly and I know
a service in which such a way is needed: emergency migration.  There is
also a product which does live migration when some hardware problems are
detected (as a semi-FT solution) -- in such cases, we cannot wait until
the guest becomes calm.

Ignoring max downtime values when we've determined that the target is no
longer converging would be another option. Essentially having a
use_strict_max_downtime that can be set on a per-migration basis, where
if not set we can "give up" on maintaining the max_downtime when it's
been determined that progress is no longer being made.

There is no need for a new parameter. Management software like ovirt/virt-manager can track the mount of pages-to-migrate left and if the number start rising, realize that the current max limit won't converge and either increase the number or cancel the migration.

Although I am not certain whether QEMU can be used for such products,
it may be worth thinking about.


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