Re: [Qemu-devel] [PATCH 1/3] use nanoseconds everywhere for timeout computation

[Anthony Liguori <anthony@codemonkey.ws>]

On 01/31/2011 03:51 PM, Paolo Bonzini wrote:
> Suggested by Aurelien Jarno.
>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
>    

Something I've found is that we have a lot of bugs that are the result 
of unit conversions when the unit can't be mapped directly to base 10.

This happens in both the PIT and RTC and probably every other fixed bus 
speed based clock we support.

I think it would be better to have a Unit argument to qemu_get_clock to 
specify the desired units.  That way, we could request NS as the time 
unit or something like PC_FREQ0 which would map to the bus speed of the PIT.

That eliminates all the unit conversion code throughout QEMU and thereby 
a big class of bugs.

Regards,

Anthony Liguori

> ---
>   qemu-timer.c |   30 +++++++++++++++---------------
>   1 files changed, 15 insertions(+), 15 deletions(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index db1ec49..60283a8 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -197,8 +197,8 @@ static void qemu_rearm_alarm_timer(struct qemu_alarm_timer *t)
>       t->rearm(t);
>   }
>
> -/* TODO: MIN_TIMER_REARM_US should be optimized */
> -#define MIN_TIMER_REARM_US 250
> +/* TODO: MIN_TIMER_REARM_NS should be optimized */
> +#define MIN_TIMER_REARM_NS 250000
>
>   #ifdef _WIN32
>
> @@ -698,11 +698,11 @@ int64_t qemu_next_deadline(void)
>
>       if (active_timers[QEMU_CLOCK_VIRTUAL]) {
>           delta = active_timers[QEMU_CLOCK_VIRTUAL]->expire_time -
> -                     qemu_get_clock(vm_clock);
> +                     qemu_get_clock_ns(vm_clock);
>       }
>       if (active_timers[QEMU_CLOCK_HOST]) {
>           int64_t hdelta = active_timers[QEMU_CLOCK_HOST]->expire_time -
> -                 qemu_get_clock(host_clock);
> +                 qemu_get_clock_ns(host_clock);
>           if (hdelta<  delta)
>               delta = hdelta;
>       }
> @@ -727,17 +727,17 @@ static uint64_t qemu_next_deadline_dyntick(void)
>       if (use_icount)
>           delta = INT32_MAX;
>       else
> -        delta = (qemu_next_deadline() + 999) / 1000;
> +        delta = qemu_next_deadline();
>
>       if (active_timers[QEMU_CLOCK_REALTIME]) {
>           rtdelta = (active_timers[QEMU_CLOCK_REALTIME]->expire_time -
> -                 qemu_get_clock(rt_clock))*1000;
> +                 qemu_get_clock_ns(rt_clock));
>           if (rtdelta<  delta)
>               delta = rtdelta;
>       }
>
> -    if (delta<  MIN_TIMER_REARM_US)
> -        delta = MIN_TIMER_REARM_US;
> +    if (delta<  MIN_TIMER_REARM_NS)
> +        delta = MIN_TIMER_REARM_NS;
>
>       return delta;
>   }
> @@ -887,8 +887,8 @@ static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
>   {
>       timer_t host_timer = (timer_t)(long)t->priv;
>       struct itimerspec timeout;
> -    int64_t nearest_delta_us = INT64_MAX;
> -    int64_t current_us;
> +    int64_t nearest_delta_ns = INT64_MAX;
> +    int64_t current_ns;
>
>       assert(alarm_has_dynticks(t));
>       if (!active_timers[QEMU_CLOCK_REALTIME]&&
> @@ -896,7 +896,7 @@ static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
>           !active_timers[QEMU_CLOCK_HOST])
>           return;
>
> -    nearest_delta_us = qemu_next_deadline_dyntick();
> +    nearest_delta_ns = qemu_next_deadline_dyntick();
>
>       /* check whether a timer is already running */
>       if (timer_gettime(host_timer,&timeout)) {
> @@ -904,14 +904,14 @@ static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
>           fprintf(stderr, "Internal timer error: aborting\n");
>           exit(1);
>       }
> -    current_us = timeout.it_value.tv_sec * 1000000 + timeout.it_value.tv_nsec/1000;
> -    if (current_us&&  current_us<= nearest_delta_us)
> +    current_ns = timeout.it_value.tv_sec * 1000000000LL + timeout.it_value.tv_nsec;
> +    if (current_ns&&  current_ns<= nearest_delta_ns)
>           return;
>
>       timeout.it_interval.tv_sec = 0;
>       timeout.it_interval.tv_nsec = 0; /* 0 for one-shot timer */
> -    timeout.it_value.tv_sec =  nearest_delta_us / 1000000;
> -    timeout.it_value.tv_nsec = (nearest_delta_us % 1000000) * 1000;
> +    timeout.it_value.tv_sec =  nearest_delta_ns / 1000000000;
> +    timeout.it_value.tv_nsec = nearest_delta_ns % 1000000000;
>       if (timer_settime(host_timer, 0 /* RELATIVE */,&timeout, NULL)) {
>           perror("settime");
>           fprintf(stderr, "Internal timer error: aborting\n");
>