* Peter Xu (pet...@redhat.com) wrote:
> On Thu, Aug 03, 2017 at 02:54:35PM +0100, Dr. David Alan Gilbert wrote:
> > * Peter Xu (pet...@redhat.com) wrote:
> > > Firstly, MigThrError enumeration is introduced to describe the error in
> > > migration_detect_error() better. This gives the migration_thread() a
> > > chance to know whether a recovery has happened.
> > >
> > > Then, if a recovery is detected, migration_thread() will reset its local
> > > variables to prepare for that.
> > >
> > > Signed-off-by: Peter Xu <pet...@redhat.com>
> > > ---
> > > migration/migration.c | 40 +++++++++++++++++++++++++++++-----------
> > > 1 file changed, 29 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index ecebe30..439bc22 100644
> > > --- a/migration/migration.c
> > > +++ b/migration/migration.c
> > > @@ -2159,6 +2159,15 @@ static bool postcopy_should_start(MigrationState
> > > *s)
> > > return atomic_read(&s->start_postcopy) || s->start_postcopy_fast;
> > > }
> > >
> > > +typedef enum MigThrError {
> > > + /* No error detected */
> > > + MIG_THR_ERR_NONE = 0,
> > > + /* Detected error, but resumed successfully */
> > > + MIG_THR_ERR_RECOVERED = 1,
> > > + /* Detected fatal error, need to exit */
> > > + MIG_THR_ERR_FATAL = 2,
> > > +} MigThrError;
> > > +
> >
> > Could you move this patch earlier to when postcopy_pause is created
> > so it's created with this enum?
>
> Sure.
>
> [...]
>
> > > @@ -2319,6 +2327,7 @@ static void *migration_thread(void *opaque)
> > > /* The active state we expect to be in; ACTIVE or POSTCOPY_ACTIVE */
> > > enum MigrationStatus current_active_state = MIGRATION_STATUS_ACTIVE;
> > > bool enable_colo = migrate_colo_enabled();
> > > + MigThrError thr_error;
> > >
> > > rcu_register_thread();
> > >
> > > @@ -2395,8 +2404,17 @@ static void *migration_thread(void *opaque)
> > > * Try to detect any kind of failures, and see whether we
> > > * should stop the migration now.
> > > */
> > > - if (migration_detect_error(s)) {
> > > + thr_error = migration_detect_error(s);
> > > + if (thr_error == MIG_THR_ERR_FATAL) {
> > > + /* Stop migration */
> > > break;
> > > + } else if (thr_error == MIG_THR_ERR_RECOVERED) {
> > > + /*
> > > + * Just recovered from a e.g. network failure, reset all
> > > + * the local variables.
> > > + */
> > > + initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > > + initial_bytes = 0;
> >
> > They don't seem that important to reset?
>
> The problem is that we have this in migration_thread():
>
> if (current_time >= initial_time + BUFFER_DELAY) {
> uint64_t transferred_bytes = qemu_ftell(s->to_dst_file) -
> initial_bytes;
> uint64_t time_spent = current_time - initial_time;
> double bandwidth = (double)transferred_bytes / time_spent;
> threshold_size = bandwidth * s->parameters.downtime_limit;
> ...
> }
>
> Here qemu_ftell() would possibly be very small since we have just
> resumed... and then transferred_bytes will be extremely huge since
> "qemu_ftell(s->to_dst_file) - initial_bytes" is actually negative...
> Then, with luck, we'll got extremely huge "bandwidth" as well.
Ah yes that's a good reason to reset it then; add a comment like
'important to avoid breaking transferred_bytes and bandwidth
calculation'
Dave
> --
> Peter Xu
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
