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Re: [Qemu-devel] [RFC 10/29] migration: new property "x-postcopy-fast"
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [RFC 10/29] migration: new property "x-postcopy-fast" |
Date: |
Wed, 2 Aug 2017 11:31:02 +0800 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Tue, Aug 01, 2017 at 09:50:02AM +0100, Dr. David Alan Gilbert wrote:
> * Peter Xu (address@hidden) wrote:
> > On Mon, Jul 31, 2017 at 07:52:24PM +0100, Dr. David Alan Gilbert wrote:
> > > * Peter Xu (address@hidden) 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.
Then let me drop this patch in next version. I do think I should avoid
introducing too many things "for debugging only"...
--
Peter Xu