Re: [PATCH v3 04/17] migration: Simplify migration_iteration_run()

[Avihai Horon]

On 08/11/2022 20:56, Vladimir Sementsov-Ogievskiy wrote:
> External email: Use caution opening links or attachments
>
>
> On 11/3/22 19:16, Avihai Horon wrote:
> > From: Juan Quintela <quintela@redhat.com>
> >
> > Signed-off-by: Juan Quintela <quintela@redhat.com>
> > Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> > ---
> >   migration/migration.c | 25 +++++++++++++------------
> >   1 file changed, 13 insertions(+), 12 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index ffe868b86f..59cc3c309b 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -3743,23 +3743,24 @@ static MigIterateState 
> > migration_iteration_run(MigrationState *s)
> >
> >       trace_migrate_pending(pending_size, s->threshold_size, 
> > pend_pre, pend_post);
> >
> > -    if (pending_size && pending_size >= s->threshold_size) {
> > -        /* Still a significant amount to transfer */
> > -        if (!in_postcopy && pend_pre <= s->threshold_size &&
> > -            qatomic_read(&s->start_postcopy)) {
> > -            if (postcopy_start(s)) {
> > -                error_report("%s: postcopy failed to start", __func__);
> > -            }
> > -            return MIG_ITERATE_SKIP;
> > -        }
> > -        /* Just another iteration step */
> > -        qemu_savevm_state_iterate(s->to_dst_file, in_postcopy);
> > -    } else {
> > +
> > +    if (pending_size < s->threshold_size) {
>
> Is corner case "pending_size == s->threshold_size == 0" theoretically 
> possible here? In this case prepatch we go to completion. Afterpatch 
> we go to next iteration..
I guess it's theoretically possible.
Let's address this corner case and keep the functional behavior exactly 
the same.

Thanks!

> > trace_migration_thread_low_pending(pending_size);
> >           migration_completion(s);
> >           return MIG_ITERATE_BREAK;
> >       }
> >
> > +    /* Still a significant amount to transfer */
> > +    if (!in_postcopy && pend_pre <= s->threshold_size &&
> > +        qatomic_read(&s->start_postcopy)) {
> > +        if (postcopy_start(s)) {
> > +            error_report("%s: postcopy failed to start", __func__);
> > +        }
> > +        return MIG_ITERATE_SKIP;
> > +    }
> > +
> > +    /* Just another iteration step */
> > +    qemu_savevm_state_iterate(s->to_dst_file, in_postcopy);
> >       return MIG_ITERATE_RESUME;
> >   }
>
> --
> Best regards,
> Vladimir