Re: [Qemu-devel] [RFC 45/48] plugin: lockstep execution support

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> Signed-off-by: Emilio G. Cota <cota@braap.org>

There are no users of this for now so I don't think this qualifies for a
first cut of the plugin API. Is the lockstep support only their for
plugins? Is there any practical use that isn't handled by non-MTTCG
round-robin and icount type scenarios?

> ---
>  include/qemu/plugin-api.h |  7 +++++++
>  include/qemu/plugin.h     |  5 +++++
>  cpus.c                    |  1 +
>  plugin.c                  | 35 +++++++++++++++++++++++++++++++++++
>  qemu-plugins.symbols      |  3 +++
>  5 files changed, 51 insertions(+)
>
> diff --git a/include/qemu/plugin-api.h b/include/qemu/plugin-api.h
> index 076353a2d2..5062e20e08 100644
> --- a/include/qemu/plugin-api.h
> +++ b/include/qemu/plugin-api.h
> @@ -227,6 +227,13 @@ typedef int64_t (*qemu_plugin_clock_func_t)(void);
>  bool qemu_plugin_register_virtual_clock(qemu_plugin_id_t id,
>                                          qemu_plugin_clock_func_t clock);
>
> +void qemu_plugin_enable_lockstep_execution(void);
> +
> +void qemu_plugin_register_lockstep_cb(qemu_plugin_id_t id,
> +                                      qemu_plugin_simple_cb_t cb);
> +
> +void qemu_plugin_end_time_slice(void);
> +
>  /* returns -1 in user-mode */
>  int qemu_plugin_n_vcpus(void);
>
> diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
> index 617161329f..c19071bdbe 100644
> --- a/include/qemu/plugin.h
> +++ b/include/qemu/plugin.h
> @@ -58,6 +58,7 @@ enum qemu_plugin_event {
>      QEMU_PLUGIN_EV_VCPU_RESUME,
>      QEMU_PLUGIN_EV_VCPU_SYSCALL,
>      QEMU_PLUGIN_EV_VCPU_SYSCALL_RET,
> +    QEMU_PLUGIN_EV_LOCKSTEP,
>      QEMU_PLUGIN_EV_FLUSH,
>      QEMU_PLUGIN_EV_ATEXIT,
>      QEMU_PLUGIN_EV_MAX,
> @@ -194,6 +195,7 @@ void qemu_plugin_atexit_cb(void);
>
>  void qemu_plugin_add_dyn_cb_arr(struct qemu_plugin_dyn_cb_arr *arr);
>  int64_t plugin_get_clock(void);
> +void plugin_lockstep_cb(void);
>
>  #else /* !CONFIG_PLUGINS */
>
> @@ -237,6 +239,9 @@ static inline
>  void qemu_plugin_add_dyn_cb_arr(struct qemu_plugin_dyn_cb_arr *arr)
>  { }
>
> +static inline void plugin_lockstep_cb(void)
> +{ }
> +
>  int64_t plugin_get_clock(void);
>
>  #endif /* !CONFIG_PLUGINS */
> diff --git a/cpus.c b/cpus.c
> index a446632a5c..8f490d1b11 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -1359,6 +1359,7 @@ static void lockstep_check_stop(CPUState *cpu)
>              /* wake up all waiting cpus */
>              lockstep_ongoing_wakeup = true;
>              n_lockstep_running_cpus = n_lockstep_cpus;
> +            plugin_lockstep_cb();
>              qemu_mutex_unlock(&lockstep_lock);
>              cpu_mutex_unlock(cpu);
>              for (i = 0; i < n_lockstep_cpus; i++) {
> diff --git a/plugin.c b/plugin.c
> index 291767f2bb..117f303249 100644
> --- a/plugin.c
> +++ b/plugin.c
> @@ -472,6 +472,7 @@ static void plugin_cb__simple(enum qemu_plugin_event ev)
>
>      switch (ev) {
>      case QEMU_PLUGIN_EV_FLUSH:
> +    case QEMU_PLUGIN_EV_LOCKSTEP:
>          QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
>              qemu_plugin_simple_cb_t func = cb->f.simple;
>
> @@ -1043,6 +1044,40 @@ int64_t plugin_get_clock(void)
>  }
>  #endif
>
> +/*
> + * We manage the CPU state changes; the plugin will control the length of the
> + * execution windows.
> + */
> +void qemu_plugin_enable_lockstep_execution(void)
> +{
> +#ifdef CONFIG_USER_ONLY
> +    abort();
> +#else
> +    cpu_lockstep_enable();
> +#endif
> +}
> +
> +void qemu_plugin_end_time_slice(void)
> +{
> +#ifdef CONFIG_USER_ONLY
> +    abort();
> +#else
> +    g_assert(current_cpu);
> +    cpu_lockstep_request_stop(current_cpu);
> +#endif
> +}
> +
> +void qemu_plugin_register_lockstep_cb(qemu_plugin_id_t id,
> +                                      qemu_plugin_simple_cb_t cb)
> +{
> +    plugin_register_cb(id, QEMU_PLUGIN_EV_LOCKSTEP, cb);
> +}
> +
> +void plugin_lockstep_cb(void)
> +{
> +    plugin_cb__simple(QEMU_PLUGIN_EV_LOCKSTEP);
> +}
> +
>  static void __attribute__((__constructor__)) plugin_init(void)
>  {
>      int i;
> diff --git a/qemu-plugins.symbols b/qemu-plugins.symbols
> index 93587b07e1..a3268a40c7 100644
> --- a/qemu-plugins.symbols
> +++ b/qemu-plugins.symbols
> @@ -1,5 +1,8 @@
>  {
>    qemu_plugin_uninstall;
> +  qemu_plugin_enable_lockstep_execution;
> +  qemu_plugin_end_time_slice;
> +  qemu_plugin_register_lockstep_cb;
>    qemu_plugin_register_vcpu_init_cb;
>    qemu_plugin_register_vcpu_exit_cb;
>    qemu_plugin_register_vcpu_idle_cb;


--
Alex Bennée