Re: [Qemu-devel] migrate_set_speed has no effect if the guest is using hugepages.

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Lin Ma (LMa@suse.com) wrote:
> Hi all,

Hi Lin,

> When I live migrate a qemu/kvm guest, If the guest is using huge pages, I found that
> the migrate_set_speed command had no effect during stage 2.

Can you explain what you mean by 'stage 2'?

> It was caused by commit 4c011c3 postcopy: Send whole huge pages
> 
> I'm wondering that is it by design or is it a bug waiting for fix?

This is the first report I've seen for it.  How did you conclude that
4c011c3 caused it?  While I can see it might have some effect on the
bandwidth management, I'm surprised it has this much effect.

What size huge pages are you using - 2MB or 1GB?
I can imagine we might have a problem that since we only do the sleep
between the hugepages, if we were using 1GB hugepages then
we'd see <big chunk of data>[sleep]<big chunk of data>[sleep]
which isn't as smooth as it used to be.

Can you give me some more details of your test?

Dave

> 
> Thanks,
> Lin
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK