Re: [Qemu-devel] [RFC PATCH v5 22/31] timer: introduce new QEMU_CLOCK_VIRTUAL_RT clock

[Paolo Bonzini <pbonzini@redhat.com>]

On 26/11/2014 11:40, Pavel Dovgalyuk wrote:
> This patch introduces new QEMU_CLOCK_VIRTUAL_RT clock, which
> should be used for icount warping. Separate timer is needed
> for replaying the execution, because warping callbacks should
> be deterministic. We cannot make realtime clock deterministic
> because it is used for screen updates and other simulator-specific
> actions. That is why we added new clock which is recorded and
> replayed when needed.
> 
> Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> ---
>  include/qemu/timer.h |    7 +++++++
>  qemu-timer.c         |    2 ++
>  replay/replay.h      |    4 +++-
>  3 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index 7b43331..df27157 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -37,12 +37,19 @@
>   * is suspended, and it will reflect system time changes the host may
>   * undergo (e.g. due to NTP). The host clock has the same precision as
>   * the virtual clock.
> + *
> + * @QEMU_CLOCK_VIRTUAL_RT: realtime clock used for icount warp
> + *
> + * This clock runs as a realtime clock, but is used for icount warp
> + * and thus should be traced with record/replay to make warp function
> + * behave deterministically.
>   */

I think it should also stop/restart across "stop" and "cont" commands,
similar to QEMU_CLOCK_VIRTUAL.  This is as simple as changing
get_clock() to cpu_get_clock().

This way, QEMU_CLOCK_VIRTUAL_RT is "what QEMU_CLOCK_VIRTUAL does without
-icount".  This makes a lot of sense and can be merged in 2.3
independent of the rest of the series.

Paolo

>  typedef enum {
>      QEMU_CLOCK_REALTIME = 0,
>      QEMU_CLOCK_VIRTUAL = 1,
>      QEMU_CLOCK_HOST = 2,
> +    QEMU_CLOCK_VIRTUAL_RT = 3,
>      QEMU_CLOCK_MAX
>  } QEMUClockType;
>  
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 8307913..3f99af5 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -567,6 +567,8 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
>              notifier_list_notify(&clock->reset_notifiers, &now);
>          }
>          return now;
> +    case QEMU_CLOCK_VIRTUAL_RT:
> +        return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, get_clock());
>      }
>  }
>  
> diff --git a/replay/replay.h b/replay/replay.h
> index 143fe85..0c02e03 100755
> --- a/replay/replay.h
> +++ b/replay/replay.h
> @@ -22,8 +22,10 @@
>  #define REPLAY_CLOCK_REAL_TICKS 0
>  /* host_clock */
>  #define REPLAY_CLOCK_HOST       1
> +/* virtual_rt_clock */
> +#define REPLAY_CLOCK_VIRTUAL_RT 2
>  
> -#define REPLAY_CLOCK_COUNT      2
> +#define REPLAY_CLOCK_COUNT      3
>  
>  extern ReplayMode replay_mode;
>  extern char *replay_image_suffix;
>