RE: [PATCH 3/3] migration/colo: Merge multi checkpoint request into one.

[Zhang, Chen]

> -----Original Message-----
> From: Zhanghailiang <zhang.zhanghailiang@huawei.com>
> Sent: Wednesday, June 3, 2020 5:39 PM
> To: Zhang, Chen <chen.zhang@intel.com>; Dr . David Alan Gilbert
> <dgilbert@redhat.com>; Juan Quintela <quintela@redhat.com>; qemu-dev
> <qemu-devel@nongnu.org>
> Cc: Zhang Chen <zhangckid@gmail.com>; Jason Wang
> <jasowang@redhat.com>
> Subject: RE: [PATCH 3/3] migration/colo: Merge multi checkpoint request
> into one.
> 
> > -----Original Message-----
> > From: Zhang, Chen [mailto:chen.zhang@intel.com]
> > Sent: Wednesday, June 3, 2020 5:11 PM
> > To: Zhanghailiang <zhang.zhanghailiang@huawei.com>; Dr . David Alan
> > Gilbert <dgilbert@redhat.com>; Juan Quintela <quintela@redhat.com>;
> > qemu-dev <qemu-devel@nongnu.org>
> > Cc: Zhang Chen <zhangckid@gmail.com>; Jason Wang
> <jasowang@redhat.com>
> > Subject: RE: [PATCH 3/3] migration/colo: Merge multi checkpoint
> > request into one.
> >
> >
> >
> > > -----Original Message-----
> > > From: Zhanghailiang <zhang.zhanghailiang@huawei.com>
> > > Sent: Tuesday, June 2, 2020 2:59 PM
> > > To: Zhang, Chen <chen.zhang@intel.com>; Dr . David Alan Gilbert
> > > <dgilbert@redhat.com>; Juan Quintela <quintela@redhat.com>; qemu-
> dev
> > > <qemu-devel@nongnu.org>
> > > Cc: Zhang Chen <zhangckid@gmail.com>; Jason Wang
> > <jasowang@redhat.com>
> > > Subject: RE: [PATCH 3/3] migration/colo: Merge multi checkpoint
> > > request into one.
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Zhang Chen [mailto:chen.zhang@intel.com]
> > > > Sent: Friday, May 15, 2020 12:28 PM
> > > > To: Dr . David Alan Gilbert <dgilbert@redhat.com>; Juan Quintela
> > > > <quintela@redhat.com>; Zhanghailiang
> > > <zhang.zhanghailiang@huawei.com>;
> > > > qemu-dev <qemu-devel@nongnu.org>
> > > > Cc: Zhang Chen <zhangckid@gmail.com>; Jason Wang
> > > > <jasowang@redhat.com>; Zhang Chen <chen.zhang@intel.com>
> > > > Subject: [PATCH 3/3] migration/colo: Merge multi checkpoint
> > > > request into one.
> > > >
> > > > From: Zhang Chen <chen.zhang@intel.com>
> > > >
> > > > When COLO guest occur issues, COLO-compare will catch lots of
> > > > different network packet and trigger notification multi times,
> > > > force periodic may happen at the same time. So this can be
> > > > efficient merge checkpoint request within
> COLO_CHECKPOINT_INTERVAL.
> > > >
> > > > Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> > > > ---
> > > >  migration/colo.c | 22 ++++++++++++++++------
> > > >  1 file changed, 16 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/migration/colo.c b/migration/colo.c index
> > > > d5bced22cb..e6a7d8c6e2 100644
> > > > --- a/migration/colo.c
> > > > +++ b/migration/colo.c
> > > > @@ -47,6 +47,9 @@ static COLOMode last_colo_mode;
> > > >
> > > >  #define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)
> > > >
> > > > +/* Default COLO_CHECKPOINT_INTERVAL is 1000 ms */ #define
> > > > +COLO_CHECKPOINT_INTERVAL 1000
> > > > +
> > > >  bool migration_in_colo_state(void)  {
> > > >      MigrationState *s = migrate_get_current(); @@ -651,13 +654,20
> > > > @@
> > > > out:
> > > >  void colo_checkpoint_notify(void *opaque)  {
> > > >      MigrationState *s = opaque;
> > > > -    int64_t next_notify_time;
> > > > +    int64_t now = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> > > >
> > > > -    qemu_sem_post(&s->colo_checkpoint_sem);
> > > > -    s->colo_checkpoint_time =
> > qemu_clock_get_ms(QEMU_CLOCK_HOST);
> > > > -    next_notify_time = s->colo_checkpoint_time +
> > > > -                    s->parameters.x_checkpoint_delay;
> > > > -    timer_mod(s->colo_delay_timer, next_notify_time);
> > > > +    /*
> > > > +     * When COLO guest occur issues, COLO-compare will catch lots of
> > > > +     * different network packet and trigger notification multi times,
> > > > +     * force periodic may happen at the same time. So this can be
> > > > +     * efficient merge checkpoint request within
> > > > COLO_CHECKPOINT_INTERVAL.
> > > > +     */
> > > > +    if (now > s->colo_checkpoint_time + COLO_CHECKPOINT_INTERVAL)
> > {
> > > > +        qemu_sem_post(&s->colo_checkpoint_sem);
> > >
> > > It is not right here, this notification should not be controlled by
> > > the interval time, I got what happened here, when multiple
> > > checkpoint requires come, this Colo_delay_time will be added every
> > > time and it will be a big value which is not what we want.
> >
> > Not just this, multi checkpoint will spend lots of resource to sync
> > memory from PVM to SVM, It will make VM stop/start multi times, but
> > for the results are same with one checkpoint.
> > So in short time just need one checkpoint, because do checkpoint still
> > need some time...
> >
> 
> Yes, this because we use semaphore here, it will be increased multiple times,
> And I think Lukas's patch 'migration/colo.c: Use event instead of semaphore'
> has fixed this problem.
> Did you try the qemu upstream which has merged this patch ?

Oh, Thanks reminder, I will drop this patch and rebase on upstream for V2.

Thank
Zhang Chen

> 
> > Thanks
> > Zhang Chen
> >
> > >
> > > Besides, please update this patch based on [PATCH 0/6] colo:
> > > migration related bugfixes series which Has modified the same place.
> > >
> > >
> > >
> > > > +        timer_mod(s->colo_delay_timer, now +
> > > > +                  s->parameters.x_checkpoint_delay);
> > > > +        s->colo_checkpoint_time = now;
> > > > +    }
> > > >  }
> > > >
> > > >  void migrate_start_colo_process(MigrationState *s)
> > > > --
> > > > 2.17.1