Re: [Qemu-devel] [RFC] save/restore with icount enabled.

[KONRAD Frédéric]

On 15/05/2013 14:50, Paolo Bonzini wrote:
> Il 15/05/2013 11:31, KONRAD Frédéric ha scritto:
> > Hi,
> >
> > We are trying to do a simple save/restore on the VM with icount enabled.
> >
> > We saw that qemu_icount_bias and qemu_icount in cpus.c are not
> > saved/restored,
> > and icount_extra, icount_decr in CPUState neither, so the vm_clock is just
> > growing normally after restoring the VM is that normal?
> >
> > We think that this is making the "replay" undeterminastic, which is bad for
> > reverse execution.
> >
> > Is there a good reason for them not being saved?
> No.  You can probably move icount to timers_state.  Something like
> zeroing qemu_icount in cpu_disable_ticks() is required in order to save
> qemu_icount_bias like the other members of timers_state.  There is even
> a dummy field that you can reuse to avoid the pain of adding a
> subsection to vmstate_timers. :)
>
> Paolo

Yes nice point :).

What about icount_extra and icount_decr defined in CPU_COMMON? in 
cpu-defs.h?

    int64_t icount_extra; /* Instructions until next timer event. */   \
    /* Number of cycles left, with interrupt flag in high bit.          \
       This allows a single read-compare-cbranch-write sequence to test \
       for both decrementer underflow and exceptions. */               \
    union {                                                             \
        uint32_t u32;                                                   \
        icount_decr_u16 u16;                                            \
    } icount_decr;                                                      \

Thanks,
Fred
> > Thanks,
> > Fred