Re: [Qemu-devel] [RFC PATCH v4 17/25] cpus: make icount warp deterministic in replay mode

["Pavel Dovgaluk" <Pavel.Dovgaluk@ispras.ru>]

> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> On 07/11/2014 11:33, Pavel Dovgalyuk wrote:
> > This patch adds saving and replaying warping parameters in record and replay
> > modes. These parameters affect on virtual clock values and therefore should
> > be deterministic.
> 
> Why are QEMU_CLOCK_REALTIME timers not recorded/replayed like
> QEMU_CLOCK_HOST is?

We cannot record all QEMU_CLOCK_REALTIME timers, because they are simulator-related timers,
not the VM-related ones. If we'll record them then we'll have to replay simulator
execution. And we want just to replay VM allowing different realtime events to be
non-replayable (like screen refresh, monitor events handling, and so on).

Pavel Dovgalyuk
> 
> > Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> > ---
> >  cpus.c |   24 +++++++++++++++++-------
> >  1 files changed, 17 insertions(+), 7 deletions(-)
> >
> > diff --git a/cpus.c b/cpus.c
> > index b41baf6..dac222b 100644
> > --- a/cpus.c
> > +++ b/cpus.c
> > @@ -370,7 +370,9 @@ static void icount_warp_rt(void *opaque)
> >
> >      seqlock_write_lock(&timers_state.vm_clock_seqlock);
> >      if (runstate_is_running()) {
> > -        int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > +        int64_t clock = qemu_clock_get_ns(replay_mode == REPLAY_MODE_NONE
> > +                                          ? QEMU_CLOCK_REALTIME
> > +                                          : QEMU_CLOCK_HOST);
> >          int64_t warp_delta;
> >
> >          warp_delta = clock - vm_clock_warp_start;
> > @@ -444,7 +446,9 @@ void qemu_clock_warp(QEMUClockType type)
> >      }
> >
> >      /* We want to use the earliest deadline from ALL vm_clocks */
> > -    clock = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> > +    clock = qemu_clock_get_ns(replay_mode == REPLAY_MODE_NONE
> > +                              ? QEMU_CLOCK_REALTIME
> > +                              : QEMU_CLOCK_HOST);
> >      deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
> >      if (deadline < 0) {
> >          return;
> > @@ -537,8 +541,10 @@ void configure_icount(QemuOpts *opts, Error **errp)
> >          return;
> >      }
> >      icount_align_option = qemu_opt_get_bool(opts, "align", false);
> > -    icount_warp_timer = timer_new_ns(QEMU_CLOCK_REALTIME,
> > -                                          icount_warp_rt, NULL);
> > +    icount_warp_timer = timer_new_ns(replay_mode == REPLAY_MODE_NONE
> > +                                     ? QEMU_CLOCK_REALTIME
> > +                                     : QEMU_CLOCK_HOST,
> > +                                     icount_warp_rt, NULL);
> >      if (strcmp(option, "auto") != 0) {
> >          errno = 0;
> >          icount_time_shift = strtol(option, &rem_str, 0);
> > @@ -562,10 +568,14 @@ void configure_icount(QemuOpts *opts, Error **errp)
> >         the virtual time trigger catches emulated time passing too fast.
> >         Realtime triggers occur even when idle, so use them less frequently
> >         than VM triggers.  */
> > -    icount_rt_timer = timer_new_ms(QEMU_CLOCK_REALTIME,
> > -                                        icount_adjust_rt, NULL);
> > +    icount_rt_timer = timer_new_ms(replay_mode == REPLAY_MODE_NONE
> > +                                   ? QEMU_CLOCK_REALTIME
> > +                                   : QEMU_CLOCK_HOST,
> > +                                   icount_adjust_rt, NULL);
> >      timer_mod(icount_rt_timer,
> > -                   qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + 1000);
> > +                   qemu_clock_get_ms(replay_mode == REPLAY_MODE_NONE
> > +                                     ? QEMU_CLOCK_REALTIME
> > +                                     : QEMU_CLOCK_HOST) + 1000);
> >      icount_vm_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> >                                          icount_adjust_vm, NULL);
> >      timer_mod(icount_vm_timer,
> >