Re: [PATCH] COLO: Move some trace code behind qemu_mutex_unlock_iothread()

[Rao, Lei]

On 12/13/2021 7:45 PM, Dr. David Alan Gilbert wrote:
> * Rao, Lei (lei.rao@intel.com) wrote:
> > Signed-off-by: Lei Rao <lei.rao@intel.com>
>
> You don't say why you want to move it - it's just a trace, what's the
> advantage?

I think it's not necessary to put trace code in the critical section.
So, moving it behind qemu_mutex_unlock_iothread() may reduce the lock time.
I will send the V2 and add some commit messages to say why.

Thanks,
Lei

> Dave
>
> > ---
> >   migration/colo.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/migration/colo.c b/migration/colo.c
> > index 2415325262..3ccacb29c8 100644
> > --- a/migration/colo.c
> > +++ b/migration/colo.c
> > @@ -683,8 +683,8 @@ static void 
> > colo_incoming_process_checkpoint(MigrationIncomingState *mis,
> >   
> >       qemu_mutex_lock_iothread();
> >       vm_stop_force_state(RUN_STATE_COLO);
> > -    trace_colo_vm_state_change("run", "stop");
> >       qemu_mutex_unlock_iothread();
> > +    trace_colo_vm_state_change("run", "stop");
> >   
> >       /* FIXME: This is unnecessary for periodic checkpoint mode */
> >       colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_REPLY,
> > @@ -786,8 +786,8 @@ static void 
> > colo_incoming_process_checkpoint(MigrationIncomingState *mis,
> >   
> >       vmstate_loading = false;
> >       vm_start();
> > -    trace_colo_vm_state_change("stop", "run");
> >       qemu_mutex_unlock_iothread();
> > +    trace_colo_vm_state_change("stop", "run");
> >   
> >       if (failover_get_state() == FAILOVER_STATUS_RELAUNCH) {
> >           return;
> > @@ -870,8 +870,8 @@ void *colo_process_incoming_thread(void *opaque)
> >           abort();
> >   #endif
> >       vm_start();
> > -    trace_colo_vm_state_change("stop", "run");
> >       qemu_mutex_unlock_iothread();
> > +    trace_colo_vm_state_change("stop", "run");
> >   
> >       colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_READY,
> >                         &local_err);
> > --
> > 2.32.0