Re: [Qemu-devel] [Qemu-ppc] broken incoming migration

[Peter Lieven <pl@kamp.de>]

On 10.06.2013 11:33, Benjamin Herrenschmidt wrote:
> On Mon, 2013-06-10 at 19:10 +1000, Alexey Kardashevskiy wrote:
>>> I would prefer not to completely drop the patch since it saves bandwidth and
>>> resources.
>> I would like migration to do what it should do - send pages no matter what,
>> this is exactly what migration is for. If there any many, many empty pages
>> (which I doubt to be a very often real life case), they could all merged in
>> big consecutive chunks and sent at the end of migration.
> I tend to agree. The problem of sending empty pages is purely a problem of
> compression. If the current mechanism is deemed "not efficient enough" for
> in the case of having lots of zero-pages, then by all means invent a better
> packet format for more tightly representing them on the wire, but don't
> break things by not sending them at all.

Ok, I see the point. I think the paradigm to say that the destination
should "decide" if it needs a page or not is a sound one.

Zero pages are quite often depending on the lifetime and the operating
system used. But a consecutive range of zero pages is only likely
in the bulk stage. I don't know if its reasonable to add a special encoding
for that.

I will sent a v2 of my previous revert patch addressing Erics concerns shortly.

Peter