Re: [Qemu-devel] [PATCH v3 04/18] trace: remove global 'uint16 dstate[]' array

[Lluís Vilanova]

Daniel P Berrange writes:

> Instead of having a global dstate array, declare a single
> 'uint16 TRACE_${EVENT_NAME}_DSTATE' variable for each
> trace event. Record a pointer to this variable in the
> TraceEvent struct too.

> By turning trace_event_get_state_dynamic_by_id into a
> macro, this still hits the fast path, and cache affinity
> is ensured by declaring all the uint16 vars adjacent to
> each other.

> Signed-off-by: Daniel P. Berrange <address@hidden>

Besides Eric's comments:

Reviewed-by: Lluís Vilanova <address@hidden>


> ---
>  scripts/tracetool/__init__.py        |  3 ++-
>  scripts/tracetool/format/events_c.py |  9 +++++++--
>  scripts/tracetool/format/events_h.py |  3 +++
>  stubs/trace-control.c                |  9 ++++-----
>  trace/control-internal.h             | 14 ++++----------
>  trace/control-target.c               | 20 ++++++++------------
>  trace/control.c                      | 11 ++---------
>  trace/event-internal.h               |  6 ++++++
>  8 files changed, 36 insertions(+), 39 deletions(-)

> diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
> index be24039..5191df9 100644
> --- a/scripts/tracetool/__init__.py
> +++ b/scripts/tracetool/__init__.py
> @@ -265,11 +265,12 @@ class Event(object):
 
>      QEMU_TRACE               = "trace_%(name)s"
>      QEMU_TRACE_TCG           = QEMU_TRACE + "_tcg"
> +    QEMU_DSTATE               = "___TRACE_%(NAME)s_DSTATE"
 
>      def api(self, fmt=None):
>          if fmt is None:
>              fmt = Event.QEMU_TRACE
> -        return fmt % {"name": self.name}
> +        return fmt % {"name": self.name, "NAME": self.name.upper()}
 
>      def transform(self, *trans):
>          """Return a new Event with transformed Arguments."""
> diff --git a/scripts/tracetool/format/events_c.py 
> b/scripts/tracetool/format/events_c.py
> index 4012063..ef873fa 100644
> --- a/scripts/tracetool/format/events_c.py
> +++ b/scripts/tracetool/format/events_c.py
> @@ -25,6 +25,9 @@ def generate(events, backend):
>          '#include "trace/control.h"',
>          '')
 
> +    for e in events:
> +        out('uint16_t %s;' % e.api(e.QEMU_DSTATE))
> +
>      out('TraceEvent trace_events[TRACE_EVENT_COUNT] = {')
 
>      for e in events:
> @@ -34,11 +37,13 @@ def generate(events, backend):
>              vcpu_id = "TRACE_VCPU_EVENT_COUNT"
>          out('    { .id = %(id)s, .vcpu_id = %(vcpu_id)s,'
>              ' .name = \"%(name)s\",'
> -            ' .sstate = %(sstate)s },',
> +            ' .sstate = %(sstate)s,',
> +            ' .dstate = &%(dstate)s, }, ',
>              id = "TRACE_" + e.name.upper(),
>              vcpu_id = vcpu_id,
>              name = e.name,
> -            sstate = "TRACE_%s_ENABLED" % e.name.upper())
> +            sstate = "TRACE_%s_ENABLED" % e.name.upper(),
> +            dstate = e.api(e.QEMU_DSTATE))
 
>      out('};',
>          '')
> diff --git a/scripts/tracetool/format/events_h.py 
> b/scripts/tracetool/format/events_h.py
> index a9da60b..03417de 100644
> --- a/scripts/tracetool/format/events_h.py
> +++ b/scripts/tracetool/format/events_h.py
> @@ -32,6 +32,9 @@ def generate(events, backend):
>      out('    TRACE_EVENT_COUNT',
>          '} TraceEventID;')
 
> +    for e in events:
> +        out('extern uint16_t %s;' % e.api(e.QEMU_DSTATE))
> +
>      # per-vCPU event identifiers
>      out('typedef enum {')
 
> diff --git a/stubs/trace-control.c b/stubs/trace-control.c
> index 2dfcd9f..dd68f25 100644
> --- a/stubs/trace-control.c
> +++ b/stubs/trace-control.c
> @@ -18,22 +18,21 @@ void trace_event_set_state_dynamic_init(TraceEvent *ev, 
> bool state)
 
>  void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
>  {
> -    TraceEventID id;
>      bool state_pre;
>      assert(trace_event_get_state_static(ev));
> -    id = trace_event_get_id(ev);
> +
>      /*
>       * We ignore the "vcpu" property here, since there's no target code. Then
>       * dstate can only be 1 or 0.
>       */
> -    state_pre = trace_events_dstate[id];
> +    state_pre = *(ev->dstate);
>      if (state_pre != state) {
>          if (state) {
>              trace_events_enabled_count++;
> -            trace_events_dstate[id] = 1;
> +            *(ev->dstate) = 1;
>          } else {
>              trace_events_enabled_count--;
> -            trace_events_dstate[id] = 0;
> +            *(ev->dstate) = 0;
>          }
>      }
>  }
> diff --git a/trace/control-internal.h b/trace/control-internal.h
> index 7f31e39..828c1fc 100644
> --- a/trace/control-internal.h
> +++ b/trace/control-internal.h
> @@ -16,7 +16,6 @@
 
 
>  extern TraceEvent trace_events[];
> -extern uint16_t trace_events_dstate[];
>  extern int trace_events_enabled_count;
 
 
> @@ -54,18 +53,13 @@ static inline bool 
> trace_event_get_state_static(TraceEvent *ev)
>      return ev->sstate;
>  }
 
> -static inline bool trace_event_get_state_dynamic_by_id(TraceEventID id)
> -{
> -    /* it's on fast path, avoid consistency checks (asserts) */
> -    return unlikely(trace_events_enabled_count) && trace_events_dstate[id];
> -}
> +/* it's on fast path, avoid consistency checks (asserts) */
> +#define trace_event_get_state_dynamic_by_id(id) \
> +    (unlikely(trace_events_enabled_count) && ___ ## id ## _DSTATE)
 
>  static inline bool trace_event_get_state_dynamic(TraceEvent *ev)
>  {
> -    TraceEventID id;
> -    assert(trace_event_get_state_static(ev));
> -    id = trace_event_get_id(ev);
> -    return trace_event_get_state_dynamic_by_id(id);
> +    return unlikely(trace_events_enabled_count) && *ev->dstate;
>  }
 
>  static inline bool trace_event_get_vcpu_state_dynamic_by_vcpu_id(CPUState 
> *vcpu,
> diff --git a/trace/control-target.c b/trace/control-target.c
> index 72081e2..c69dda9 100644
> --- a/trace/control-target.c
> +++ b/trace/control-target.c
> @@ -15,21 +15,20 @@
 
>  void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state)
>  {
> -    TraceEventID id = trace_event_get_id(ev);
>      bool state_pre;
>      assert(trace_event_get_state_static(ev));
>      /*
>       * We ignore the "vcpu" property here, since no vCPUs have been created
>       * yet. Then dstate can only be 1 or 0.
>       */
> -    state_pre = trace_events_dstate[id];
> +    state_pre = *ev->dstate;
>      if (state_pre != state) {
>          if (state) {
>              trace_events_enabled_count++;
> -            trace_events_dstate[id] = 1;
> +            *ev->dstate = 1;
>          } else {
>              trace_events_enabled_count--;
> -            trace_events_dstate[id] = 0;
> +            *ev->dstate = 0;
>          }
>      }
>  }
> @@ -44,15 +43,14 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool 
> state)
>          }
>      } else {
>          /* Without the "vcpu" property, dstate can only be 1 or 0 */
> -        TraceEventID id = trace_event_get_id(ev);
> -        bool state_pre = trace_events_dstate[id];
> +        bool state_pre = *ev->dstate;
>          if (state_pre != state) {
>              if (state) {
>                  trace_events_enabled_count++;
> -                trace_events_dstate[id] = 1;
> +                *ev->dstate = 1;
>              } else {
>                  trace_events_enabled_count--;
> -                trace_events_dstate[id] = 0;
> +                *ev->dstate = 0;
>              }
>          }
>      }
> @@ -61,23 +59,21 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool 
> state)
>  void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
>                                          TraceEvent *ev, bool state)
>  {
> -    TraceEventID id;
>      TraceEventVCPUID vcpu_id;
>      bool state_pre;
>      assert(trace_event_get_state_static(ev));
>      assert(trace_event_is_vcpu(ev));
> -    id = trace_event_get_id(ev);
>      vcpu_id = trace_event_get_vcpu_id(ev);
>      state_pre = test_bit(vcpu_id, vcpu->trace_dstate);
>      if (state_pre != state) {
>          if (state) {
>              trace_events_enabled_count++;
>              set_bit(vcpu_id, vcpu->trace_dstate);
> -            trace_events_dstate[id]++;
> +            (*ev->dstate)++;
>          } else {
>              trace_events_enabled_count--;
>              clear_bit(vcpu_id, vcpu->trace_dstate);
> -            trace_events_dstate[id]--;
> +            (*ev->dstate)--;
>          }
>      }
>  }
> diff --git a/trace/control.c b/trace/control.c
> index 303b3f3..c681fa0 100644
> --- a/trace/control.c
> +++ b/trace/control.c
> @@ -28,12 +28,6 @@
>  #include "monitor/monitor.h"
 
>  int trace_events_enabled_count;
> -/*
> - * Interpretation depends on wether the event has the 'vcpu' property:
> - * - false: Boolean value indicating whether the event is active.
> - * - true : Integral counting the number of vCPUs that have this event 
> enabled.
> - */
> -uint16_t trace_events_dstate[TRACE_EVENT_COUNT];
 
>  QemuOptsList qemu_trace_opts = {
>      .name = "trace",
> @@ -294,11 +288,10 @@ void trace_init_vcpu_events(void)
>          if (trace_event_is_vcpu(ev) &&
>              trace_event_get_state_static(ev) &&
>              trace_event_get_state_dynamic(ev)) {
> -            TraceEventID id = trace_event_get_id(ev);
>              /* check preconditions */
> -            assert(trace_events_dstate[id] == 1);
> +            assert(*ev->dstate == 1);
>              /* disable early-init state ... */
> -            trace_events_dstate[id] = 0;
> +            *ev->dstate = 0;
>              trace_events_enabled_count--;
>              /* ... and properly re-enable */
>              trace_event_set_state_dynamic(ev, true);
> diff --git a/trace/event-internal.h b/trace/event-internal.h
> index 074faf6..3b9ceb5 100644
> --- a/trace/event-internal.h
> +++ b/trace/event-internal.h
> @@ -19,6 +19,11 @@
>   * @vcpu_id: Unique per-vCPU event identifier.
>   * @name: Event name.
>   * @sstate: Static tracing state.
> + * @dstate: Dynamic tracing state
> + *
> + * Interpretation of @dstate depends on wether the event has the 'vcpu' 
> property:
> + * - false: Boolean value indicating whether the event is active.
> + * - true : Integral counting the number of vCPUs that have this event 
> enabled.
>   *
>   * Opaque generic description of a tracing event.
>   */
> @@ -27,6 +32,7 @@ typedef struct TraceEvent {
>      TraceEventVCPUID vcpu_id;
>      const char * name;
>      const bool sstate;
> +    uint16_t *dstate;
>  } TraceEvent;
 
>  void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state);
> -- 
> 2.7.4