Re: [Qemu-devel] [RFC PATCH v3 30/30] replay: don't process async events when warping the clock

[Pavel Dovgalyuk]

> From: Paolo Bonzini [mailto:address@hidden On Behalf Of Paolo Bonzini
> On 11/01/2018 09:27, Pavel Dovgalyuk wrote:
> > Virtual clock is wapred from iothread and vcpu thread. When the hardware
> > events associated with warp checkpoint, then interrupt delivering may be
> > non-deterministic if checkpoint is processed in different threads in record
> > and replay.
> > This patch disables event processing for clock warp checkpoint and leaves
> > all hardware events to other checkpoints (e.g., virtual clock).
> >
> > Signed-off-by: Pavel Dovgalyuk <address@hidden>
> > ---
> >  replay/replay.c |    7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/replay/replay.c b/replay/replay.c
> > index b9c496a..cc43c38 100644
> > --- a/replay/replay.c
> > +++ b/replay/replay.c
> > @@ -211,7 +211,12 @@ bool replay_checkpoint(ReplayCheckpoint checkpoint)
> >      } else if (replay_mode == REPLAY_MODE_RECORD) {
> >          g_assert(replay_mutex_locked());
> >          replay_put_event(EVENT_CHECKPOINT + checkpoint);
> > -        replay_save_events(checkpoint);
> > +        /* This checkpoint belongs to several threads.
> > +           Processing events from different threads is
> > +           non-deterministic */
> > +        if (checkpoint != CHECKPOINT_CLOCK_WARP_START) {
> > +            replay_save_events(checkpoint);
> > +        }
> >          res = true;
> >      }
> >  out:
> >
> 
> Please add an assertion in replay_read_event that the read_checkpoint is
> never CHECKPOINT_CLOCK_WARP_START. 

Ok.
 
> Why is the checkpoint still needed?

Because it synchronizes the warp itself.

Pavel Dovgalyuk