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

["Pavel Dovgaluk" <Pavel.Dovgaluk@ispras.ru>]

> From: Paolo Bonzini [mailto:pbonzini@redhat.com]
> 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 <pavel.dovgaluk@ispras.ru>
> > ---
> >  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?

Not really. Frederic's QEMU_CLOCK_ICOUNT is measured in nanoseconds.
And this counter is measured in instructions.

Pavel Dovgalyuk