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

[Frederic Konrad]

On 07/11/2014 12:36, Pavel Dovgaluk wrote:
> > From: Paolo Bonzini [mailto:address@hidden
> > 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?
> Not really. Frederic's QEMU_CLOCK_ICOUNT is measured in nanoseconds.
> And this counter is measured in instructions.
>
> Pavel Dovgalyuk
So you transformed your implementation to use icount?
I didn't saw that in the cover letter.

I guess you replay event's according to the current instruction?
I implemented icount clock with the QEMUTimer API so a callback can be
notified during the replay at the right instruction.

By the way do you have a git tree somewhere where I can get the patches?

Fred