Re: [Qemu-devel] [RFC 10/29] migration: new property "x-postcopy-fast"

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

* Peter Xu (peterx@redhat.com) wrote:
> On Mon, Jul 31, 2017 at 07:52:24PM +0100, Dr. David Alan Gilbert wrote:
> > * Peter Xu (peterx@redhat.com) wrote:
> > > This provides a way to start postcopy ASAP when migration starts. To do
> > > this, we need both:
> > > 
> > >   -global migration.x-postcopy-ram=on \
> > >   -global migration.x-postcopy-fast=on
> > 
> > Can you explain why this is necessary?  Both sides already know
> > they're doing a postcopy recovery don't they?
> 
> What I wanted to do here is to provide a way to start postcopy at the
> very beginning (actually it'll possibly start postcopy at the first
> loop in migration_thread), instead of start postcopy until we trigger
> it using "migrate_start_postcopy" command.
> 
> I used it for easier debugging (so I don't need to type
> "migrate_start_postcopy" every time when I trigger postcopy
> migration), meanwhile I think it can also be used when someone really
> want to start postcopy from the very beginning.
> 
> Would such a new parameter makes sense?

Other than debugging, I don't think there's a real use for it; the
slight delay between starting migration and triggering postcopy has
very little cost.

Dave

> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK