Re: [Qemu-devel] [PATCH 03/10] cpu: init vmstate for ticks and clock offset

[Juan Quintela]

Paolo Bonzini <address@hidden> wrote:
> From: Pavel Dovgalyuk <address@hidden>
>
> Ticks and clock offset used by CPU timers have to be saved in vmstate.
> But vmstate for these fields registered only in icount mode.
> Missing registration leads to breaking the continuity when vmstate is loaded.
> This patch introduces new initialization function which fixes this.
>
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>

Nack.

This break migration when using with older machine types.

Several questions before I propose an alternative:
- are we this fields always needed (then why migration has worked until
  now)
- after reding cpus.c the question is .... why it ever worked?


After reading cpus.c, it appears that we only really need this
functionality for

qemu_clock_get_ns()

when called with QEMU_CLOCK_VIRTUAL with icount disabled, right?

further grep shows that it is used for acpi_pm_tmr_get_clock, whatever
that is.  When is this used, thanks?

Later, Juan.

> ---
>  cpus.c                | 8 ++++++--
>  include/qemu-common.h | 2 ++
>  vl.c                  | 1 +
>  3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 0f7d0ea..2a0e133 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -493,13 +493,17 @@ static const VMStateDescription vmstate_timers = {
>      }
>  };
>  
> +void cpu_ticks_init(void)
> +{
> +    seqlock_init(&timers_state.vm_clock_seqlock, NULL);
> +    vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
> +}
> +
>  void configure_icount(QemuOpts *opts, Error **errp)
>  {
>      const char *option;
>      char *rem_str = NULL;
>  
> -    seqlock_init(&timers_state.vm_clock_seqlock, NULL);
> -    vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
>      option = qemu_opt_get(opts, "shift");
>      if (!option) {
>          if (qemu_opt_get(opts, "align") != NULL) {
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index bcf7a6a..dcb57ab 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -105,6 +105,8 @@ static inline char *realpath(const char *path, char 
> *resolved_path)
>  }
>  #endif
>  
> +void cpu_ticks_init(void);
> +
>  /* icount */
>  void configure_icount(QemuOpts *opts, Error **errp);
>  extern int use_icount;
> diff --git a/vl.c b/vl.c
> index 15aea95..5db0d08 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4334,6 +4334,7 @@ int main(int argc, char **argv, char **envp)
>      qemu_spice_init();
>  #endif
>  
> +    cpu_ticks_init();
>      if (icount_opts) {
>          if (kvm_enabled() || xen_enabled()) {
>              fprintf(stderr, "-icount is not allowed with kvm or xen\n");