Re: [Qemu-devel] [PATCHv2] [RFC 1/7] aio / timers: Remove alarm timers

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sat, Jul 20, 2013 at 07:06:37PM +0100, Alex Bligh wrote:
> Remove alarm timers from qemu-timers.c in anticipation of using
> timeouts for g_poll / p_poll instead.
> 
> Signed-off-by: Alex Bligh <alex@alex.org.uk>
> ---
>  include/qemu/timer.h |    2 -
>  main-loop.c          |    4 -
>  qemu-timer.c         |  501 +-------------------------------------------------
>  vl.c                 |    5 +-
>  4 files changed, 7 insertions(+), 505 deletions(-)

This should be one of the last patches so qemu.git remains bisectable.
Only remove the alarm timer once the event loops are already using the
timeout argument.

> @@ -245,11 +82,7 @@ static QEMUClock *qemu_new_clock(int type)
>  
>  void qemu_clock_enable(QEMUClock *clock, bool enabled)
>  {
> -    bool old = clock->enabled;
>      clock->enabled = enabled;
> -    if (enabled && !old) {
> -        qemu_rearm_alarm_timer(alarm_timer);
> -    }

If this function is supposed to work when called from another thread
(e.g. vcpu thread), then you need to call qemu_notify_event().  For
AioContext clocks that should be aio_notify() with the relevant
AioContext, but we don't need that yet.

>  }
>  
>  int64_t qemu_clock_has_timers(QEMUClock *clock)
> @@ -340,10 +173,9 @@ void qemu_mod_timer_ns(QEMUTimer *ts, int64_t expire_time)
>  
>      /* Rearm if necessary  */
>      if (pt == &ts->clock->active_timers) {
> -        if (!alarm_timer->pending) {
> -            qemu_rearm_alarm_timer(alarm_timer);
> -        }
> -        /* Interrupt execution to force deadline recalculation.  */
> +        /* Interrupt execution to force deadline recalculation.
> +         * FIXME: Do we need to do this now?
> +         */
>          qemu_clock_warp(ts->clock);
>          if (use_icount) {
>              qemu_notify_event();

Same here.

> diff --git a/vl.c b/vl.c
> index 25b8f2f..612c609 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3714,7 +3714,10 @@ int main(int argc, char **argv, char **envp)
>                  old_param = 1;
>                  break;
>              case QEMU_OPTION_clock:
> -                configure_alarms(optarg);
> +                /* Once upon a time we did:
> +                 *   configure_alarms(optarg);
> +                 * here. This is stubbed out for compatibility.
> +                 */
>                  break;

This could be made clearer to say outright that the options don't exist
anymore:

/* Clock options no longer exist.  Keep this option for backward
 * compatibility.
 */