Re: [Qemu-devel] [RFC PATCH v4 07/25] icount: implement icount requesting

[Paolo Bonzini]

On 07/11/2014 11:32, Pavel Dovgalyuk wrote:
> Replay uses number of executed instructions to determine corrent events
> injection moments. This patch introduces new function for querying the
> instructions counter.
> 
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> ---
>  cpus.c               |   26 +++++++++++++++++++++++---
>  include/qemu/timer.h |    1 +
>  2 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/cpus.c b/cpus.c
> index 7e8c507..2ec6d75 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -136,8 +136,7 @@ typedef struct TimersState {
>  
>  static TimersState timers_state;
>  
> -/* Return the virtual CPU time, based on the instruction counter.  */
> -static int64_t cpu_get_icount_locked(void)
> +static int64_t cpu_get_instructions_counter_locked(void)
>  {
>      int64_t icount;
>      CPUState *cpu = current_cpu;
> @@ -145,10 +144,31 @@ static int64_t cpu_get_icount_locked(void)
>      icount = timers_state.qemu_icount;
>      if (cpu) {
>          if (!cpu_can_do_io(cpu)) {
> -            fprintf(stderr, "Bad clock read\n");
> +            fprintf(stderr, "Bad icount read\n");
> +            exit(1);
>          }
>          icount -= (cpu->icount_decr.u16.low + cpu->icount_extra);
>      }
> +    return icount;
> +}
> +
> +int64_t cpu_get_instructions_counter(void)
> +{
> +    /* This function calls are synchnonized to timer changes,
> +       calling cpu_get_instructions_counter_locked without lock is safe */
> +    int64_t icount = timers_state.qemu_icount;
> +    CPUState *cpu = current_cpu;
> +
> +    if (cpu) {
> +        icount -= (cpu->icount_decr.u16.low + cpu->icount_extra);
> +    }
> +    return icount;
> +}

This is the same as Frederic's QEMU_CLOCK_ICOUNT clock, right?  Any
reason why one is better than the other?

Paolo

> +/* Return the virtual CPU time, based on the instruction counter.  */
> +static int64_t cpu_get_icount_locked(void)
> +{
> +    int64_t icount = cpu_get_instructions_counter_locked();
>      return timers_state.qemu_icount_bias + cpu_icount_to_ns(icount);
>  }
>  
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index 5f5210d..38a02c5 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -743,6 +743,7 @@ static inline int64_t get_clock(void)
>  #endif
>  
>  /* icount */
> +int64_t cpu_get_instructions_counter(void);
>  int64_t cpu_get_icount(void);
>  int64_t cpu_get_clock(void);
>  int64_t cpu_get_clock_offset(void);
>