Re: [Qemu-devel] [RFC] [PATCHv4 01/13] aio / timers: add qemu-timer.c utility functions

[Paolo Bonzini]

 On Jul 26 2013, Alex Bligh wrote:
> Add qemu_free_clock and expose qemu_new_clock and clock types.
> 
> Add utility functions to qemu-timer.c for nanosecond timing.
> 
> Add qemu_clock_deadline_ns to calculate deadlines to
> nanosecond accuracy.
> 
> Add utility function qemu_soonest_timeout to calculate soonest deadline.
> 
> Add qemu_timeout_ns_to_ms to convert a timeout in nanoseconds back to
> milliseconds for when ppoll is not used.
> 
> Signed-off-by: Alex Bligh <address@hidden>
> ---
>  include/qemu/timer.h |   17 ++++++++++++++
>  qemu-timer.c         |   63 
> +++++++++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 74 insertions(+), 6 deletions(-)
> 
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index 9dd206c..6171db3 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -11,6 +11,10 @@
>  #define SCALE_US 1000
>  #define SCALE_NS 1
>  
> +#define QEMU_CLOCK_REALTIME 0
> +#define QEMU_CLOCK_VIRTUAL  1
> +#define QEMU_CLOCK_HOST     2
> +
>  typedef struct QEMUClock QEMUClock;
>  typedef void QEMUTimerCB(void *opaque);
>  
> @@ -32,10 +36,14 @@ extern QEMUClock *vm_clock;
>     the virtual clock. */
>  extern QEMUClock *host_clock;
>  
> +QEMUClock *qemu_new_clock(int type);
> +void qemu_free_clock(QEMUClock *clock);
>  int64_t qemu_get_clock_ns(QEMUClock *clock);
>  int64_t qemu_clock_has_timers(QEMUClock *clock);
>  int64_t qemu_clock_expired(QEMUClock *clock);
>  int64_t qemu_clock_deadline(QEMUClock *clock);
> +int64_t qemu_clock_deadline_ns(QEMUClock *clock);
> +int qemu_timeout_ns_to_ms(int64_t ns);
>  void qemu_clock_enable(QEMUClock *clock, bool enabled);
>  void qemu_clock_warp(QEMUClock *clock);
>  
> @@ -63,6 +71,15 @@ int64_t cpu_get_ticks(void);
>  void cpu_enable_ticks(void);
>  void cpu_disable_ticks(void);
>  
> +static inline int64_t qemu_soonest_timeout(int64_t timeout1, int64_t 
> timeout2)
> +{
> +    /* we can abuse the fact that -1 (which means infinite) is a maximal
> +     * value when cast to unsigned. As this is disgusting, it's kept in
> +     * one inline function.
> +     */
> +    return ((uint64_t) timeout1 < (uint64_t) timeout2) ? timeout1 : timeout2;
> +}
> +

It becomes much less disgusting if timeouts are made unsigned.  I agree
we can do it later.

>  static inline QEMUTimer *qemu_new_timer_ns(QEMUClock *clock, QEMUTimerCB *cb,
>                                             void *opaque)
>  {
> diff --git a/qemu-timer.c b/qemu-timer.c
> index b2d95e2..3dfbdbf 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -40,10 +40,6 @@
>  /***********************************************************/
>  /* timers */
>  
> -#define QEMU_CLOCK_REALTIME 0
> -#define QEMU_CLOCK_VIRTUAL  1
> -#define QEMU_CLOCK_HOST     2
> -
>  struct QEMUClock {
>      QEMUTimer *active_timers;
>  
> @@ -231,7 +227,7 @@ QEMUClock *rt_clock;
>  QEMUClock *vm_clock;
>  QEMUClock *host_clock;
>  
> -static QEMUClock *qemu_new_clock(int type)
> +QEMUClock *qemu_new_clock(int type)
>  {
>      QEMUClock *clock;
>  
> @@ -243,6 +239,11 @@ static QEMUClock *qemu_new_clock(int type)
>      return clock;
>  }
>  
> +void qemu_free_clock(QEMUClock *clock)
> +{
> +    g_free(clock);
> +}
> +
>  void qemu_clock_enable(QEMUClock *clock, bool enabled)
>  {
>      bool old = clock->enabled;
> @@ -268,7 +269,7 @@ int64_t qemu_clock_deadline(QEMUClock *clock)
>      /* To avoid problems with overflow limit this to 2^32.  */
>      int64_t delta = INT32_MAX;
>  
> -    if (clock->active_timers) {
> +    if (clock->enabled && clock->active_timers) {
>          delta = clock->active_timers->expire_time - qemu_get_clock_ns(clock);
>      }
>      if (delta < 0) {
> @@ -277,6 +278,56 @@ int64_t qemu_clock_deadline(QEMUClock *clock)
>      return delta;
>  }
>  
> +/*
> + * As above, but return -1 for no deadline, and do not cap to 2^32
> + * as we know the result is always positive.
> + */
> +
> +int64_t qemu_clock_deadline_ns(QEMUClock *clock)
> +{
> +    int64_t delta;
> +
> +    if (!clock->enabled || !clock->active_timers) {
> +        return -1;
> +    }
> +
> +    delta = clock->active_timers->expire_time - qemu_get_clock_ns(clock);
> +
> +    if (delta <= 0) {
> +        return 0;
> +    }
> +
> +    return delta;
> +}
> +
> +/* Transition function to convert a nanosecond timeout to ms
> + * This is used where a system does not support ppoll
> + */
> +int qemu_timeout_ns_to_ms(int64_t ns)
> +{
> +    int64_t ms;
> +    if (ns < 0) {
> +        return -1;
> +    }
> +
> +    if (!ns) {
> +        return 0;
> +    }
> +
> +    /* Always round up, because it's better to wait too long than to wait too
> +     * little and effectively busy-wait
> +     */
> +    ms = (ns + SCALE_MS - 1) / SCALE_MS;
> +
> +    /* To avoid overflow problems, limit this to 2^31, i.e. approx 25 days */
> +    if (ms > (int64_t) INT32_MAX) {
> +        ms = INT32_MAX;
> +    }
> +
> +    return (int) ms;
> +}
> +
> +
>  QEMUTimer *qemu_new_timer(QEMUClock *clock, int scale,
>                            QEMUTimerCB *cb, void *opaque)
>  {
> -- 
> 1.7.9.5
>