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

[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.  Why is the checkpoint still needed?

Thanks,

Paolo