[Qemu-devel] [PATCH v3 0/2] trace: Simplify late initialization

[Qemu-devel] [PATCH v3 0/2] trace: Simplify late initialization

[Lluís Vilanova]

Removes the need for 'trace_events_dstate_init' and does a little cleanup in how
state values are modified (to avoid implicit conversions from bool).

Changes in v2
=============

* Fix late-init state value [Daniel P. Berrange].

Changes in v3
=============

* Avoid implicit conversions from bool to integers (second patch) [Daniel
  P. Berrange].

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
---

Lluís Vilanova (2):
      trace: Remove 'trace_events_dstate_init'
      trace: Avoid implicit bool->integer conversions


 stubs/trace-control.c  |   14 ++++++++++++--
 trace/control-target.c |   23 +++++++++++++++++++++--
 trace/control.c        |   23 ++++++++++-------------
 trace/control.h        |    3 +++
 trace/event-internal.h |    1 +
 5 files changed, 47 insertions(+), 17 deletions(-)


To: qemu-devel@nongnu.org
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: 'Daniel P. Berrange' <berrange@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>

[Qemu-devel] [PATCH v3 1/2] trace: Remove 'trace_events_dstate_init'

[Lluís Vilanova]

Removes the event state array used for early initialization. Since only
events with the "vcpu" property need a late initialization fixup,
threats their initialization specially.

Assumes that the user won't touch the state of "vcpu" events between
early and late initialization (e.g., through QMP).

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
---
 stubs/trace-control.c  |    5 +++++
 trace/control-target.c |    9 +++++++++
 trace/control.c        |   23 ++++++++++-------------
 trace/control.h        |    3 +++
 trace/event-internal.h |    1 +
 5 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/stubs/trace-control.c b/stubs/trace-control.c
index fe59836..3740c38 100644
--- a/stubs/trace-control.c
+++ b/stubs/trace-control.c
@@ -11,6 +11,11 @@
 #include "trace/control.h"
 
 
+void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state)
+{
+    trace_event_set_state_dynamic(ev, state);
+}
+
 void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
 {
     TraceEventID id;
diff --git a/trace/control-target.c b/trace/control-target.c
index 74c029a..4ee3733 100644
--- a/trace/control-target.c
+++ b/trace/control-target.c
@@ -13,6 +13,15 @@
 #include "translate-all.h"
 
 
+void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state)
+{
+    TraceEventID id = trace_event_get_id(ev);
+    assert(trace_event_get_state_static(ev));
+    /* Ignore "vcpu" property, since no vCPUs have been created yet */
+    trace_events_enabled_count += state - trace_events_dstate[id];
+    trace_events_dstate[id] = state;
+}
+
 void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
 {
     CPUState *vcpu;
diff --git a/trace/control.c b/trace/control.c
index d173c09..f6e06cc 100644
--- a/trace/control.c
+++ b/trace/control.c
@@ -31,8 +31,6 @@ int trace_events_enabled_count;
  * - true : Integral counting the number of vCPUs that have this event enabled.
  */
 uint16_t trace_events_dstate[TRACE_EVENT_COUNT];
-/* Marks events for late vCPU state init */
-static bool trace_events_dstate_init[TRACE_EVENT_COUNT];
 
 QemuOptsList qemu_trace_opts = {
     .name = "trace",
@@ -142,10 +140,7 @@ static void do_trace_enable_events(const char *line_buf)
         TraceEvent *ev = NULL;
         while ((ev = trace_event_pattern(line_ptr, ev)) != NULL) {
             if (trace_event_get_state_static(ev)) {
-                /* start tracing */
-                trace_event_set_state_dynamic(ev, enable);
-                /* mark for late vCPU init */
-                trace_events_dstate_init[ev->id] = true;
+                trace_event_set_state_dynamic_init(ev, enable);
             }
         }
     } else {
@@ -157,10 +152,7 @@ static void do_trace_enable_events(const char *line_buf)
             error_report("WARNING: trace event '%s' is not traceable",
                          line_ptr);
         } else {
-            /* start tracing */
-            trace_event_set_state_dynamic(ev, enable);
-            /* mark for late vCPU init */
-            trace_events_dstate_init[ev->id] = true;
+            trace_event_set_state_dynamic_init(ev, enable);
         }
     }
 }
@@ -275,9 +267,14 @@ void trace_init_vcpu_events(void)
 {
     TraceEvent *ev = NULL;
     while ((ev = trace_event_pattern("*", ev)) != NULL) {
-        if (trace_event_is_vcpu(ev) &&
-            trace_event_get_state_static(ev) &&
-            trace_events_dstate_init[ev->id]) {
+        if (trace_event_is_vcpu(ev) && trace_event_get_state_dynamic(ev)) {
+            TraceEventID id = trace_event_get_id(ev);
+            /* check preconditions */
+            assert(trace_events_dstate[id] == 1);
+            /* disable early-init state ... */
+            trace_events_dstate[id] = 0;
+            trace_events_enabled_count--;
+            /* ... and properly re-enable */
             trace_event_set_state_dynamic(ev, true);
         }
     }
diff --git a/trace/control.h b/trace/control.h
index 0413b28..27a16fc 100644
--- a/trace/control.h
+++ b/trace/control.h
@@ -274,6 +274,9 @@ char *trace_opt_parse(const char *optarg);
  *
  * Re-synchronize initial event state with vCPUs (which can be created after
  * trace_init_events()).
+ *
+ * Precondition: event states won't be changed between trace_enable_events() and
+ * trace_init_vcpu_events() (e.g., through QMP).
  */
 void trace_init_vcpu_events(void);
 
diff --git a/trace/event-internal.h b/trace/event-internal.h
index 5d8fa97..074faf6 100644
--- a/trace/event-internal.h
+++ b/trace/event-internal.h
@@ -29,5 +29,6 @@ typedef struct TraceEvent {
     const bool sstate;
 } TraceEvent;
 
+void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state);
 
 #endif /* TRACE__EVENT_INTERNAL_H */

[Qemu-devel] [PATCH v3 2/2] trace: Avoid implicit bool->integer conversions

[Lluís Vilanova]

An explicit if/else is clearer than arithmetic assuming #true is 1,
while the compiler should be able to generate just as optimal code.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
---
 stubs/trace-control.c  |    9 +++++++--
 trace/control-target.c |   18 ++++++++++++++----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/stubs/trace-control.c b/stubs/trace-control.c
index 3740c38..099c2b5 100644
--- a/stubs/trace-control.c
+++ b/stubs/trace-control.c
@@ -21,8 +21,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
     TraceEventID id;
     assert(trace_event_get_state_static(ev));
     id = trace_event_get_id(ev);
-    trace_events_enabled_count += state - trace_events_dstate[id];
-    trace_events_dstate[id] = state;
+    if (state) {
+        trace_events_enabled_count++;
+        trace_events_dstate[id] = 1;
+    } else {
+        trace_events_enabled_count--;
+        trace_events_dstate[id] = 0;
+    }
 }
 
 void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
diff --git a/trace/control-target.c b/trace/control-target.c
index 4ee3733..4e2e727 100644
--- a/trace/control-target.c
+++ b/trace/control-target.c
@@ -18,8 +18,13 @@ void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state)
     TraceEventID id = trace_event_get_id(ev);
     assert(trace_event_get_state_static(ev));
     /* Ignore "vcpu" property, since no vCPUs have been created yet */
-    trace_events_enabled_count += state - trace_events_dstate[id];
-    trace_events_dstate[id] = state;
+    if (state) {
+        trace_events_enabled_count++;
+        trace_events_dstate[id] = 1;
+    } else {
+        trace_events_enabled_count--;
+        trace_events_dstate[id] = 0;
+    }
 }
 
 void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
@@ -32,8 +37,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
         }
     } else {
         TraceEventID id = trace_event_get_id(ev);
-        trace_events_enabled_count += state - trace_events_dstate[id];
-        trace_events_dstate[id] = state;
+        if (state) {
+            trace_events_enabled_count++;
+            trace_events_dstate[id] = 1;
+        } else {
+            trace_events_enabled_count--;
+            trace_events_dstate[id] = 0;
+        }
     }
 }
 

Re: [Qemu-devel] [PATCH v3 2/2] trace: Avoid implicit bool->integer conversions

[Daniel P. Berrange]

On Thu, Aug 11, 2016 at 06:11:29PM +0200, Lluís Vilanova wrote:
> An explicit if/else is clearer than arithmetic assuming #true is 1,
> while the compiler should be able to generate just as optimal code.
> 
> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
> ---
>  stubs/trace-control.c  |    9 +++++++--
>  trace/control-target.c |   18 ++++++++++++++----
>  2 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/stubs/trace-control.c b/stubs/trace-control.c
> index 3740c38..099c2b5 100644
> --- a/stubs/trace-control.c
> +++ b/stubs/trace-control.c
> @@ -21,8 +21,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
>      TraceEventID id;
>      assert(trace_event_get_state_static(ev));
>      id = trace_event_get_id(ev);
> -    trace_events_enabled_count += state - trace_events_dstate[id];
> -    trace_events_dstate[id] = state;
> +    if (state) {
> +        trace_events_enabled_count++;
> +        trace_events_dstate[id] = 1;
> +    } else {
> +        trace_events_enabled_count--;

SHouldn't this be trace_events_enabled_count -= trace_events_dstate[id];
as it is possible to call this method for a trace event that is a per-vcpu
event

> +        trace_events_dstate[id] = 0;
> +    }
>  }
>  
>  void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
> diff --git a/trace/control-target.c b/trace/control-target.c
> index 4ee3733..4e2e727 100644
> --- a/trace/control-target.c
> +++ b/trace/control-target.c
> @@ -18,8 +18,13 @@ void trace_event_set_state_dynamic_init(TraceEvent *ev, bool state)
>      TraceEventID id = trace_event_get_id(ev);
>      assert(trace_event_get_state_static(ev));
>      /* Ignore "vcpu" property, since no vCPUs have been created yet */
> -    trace_events_enabled_count += state - trace_events_dstate[id];
> -    trace_events_dstate[id] = state;
> +    if (state) {
> +        trace_events_enabled_count++;
> +        trace_events_dstate[id] = 1;
> +    } else {
> +        trace_events_enabled_count--;
> +        trace_events_dstate[id] = 0;
> +    }


>  }
>  
>  void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
> @@ -32,8 +37,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
>          }
>      } else {
>          TraceEventID id = trace_event_get_id(ev);
> -        trace_events_enabled_count += state - trace_events_dstate[id];
> -        trace_events_dstate[id] = state;
> +        if (state) {
> +            trace_events_enabled_count++;
> +            trace_events_dstate[id] = 1;
> +        } else {
> +            trace_events_enabled_count--;
> +            trace_events_dstate[id] = 0;
> +        }
>      }
>  }
>  
> 

Regards,
Daniel
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Re: [Qemu-devel] [PATCH v3 2/2] trace: Avoid implicit bool->integer conversions

[Lluís Vilanova]

Daniel P Berrange writes:

> On Thu, Aug 11, 2016 at 06:11:29PM +0200, Lluís Vilanova wrote:
>> An explicit if/else is clearer than arithmetic assuming #true is 1,
>> while the compiler should be able to generate just as optimal code.
>> 
>> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
>> ---
>> stubs/trace-control.c  |    9 +++++++--
>> trace/control-target.c |   18 ++++++++++++++----
>> 2 files changed, 21 insertions(+), 6 deletions(-)
>> 
>> diff --git a/stubs/trace-control.c b/stubs/trace-control.c
>> index 3740c38..099c2b5 100644
>> --- a/stubs/trace-control.c
>> +++ b/stubs/trace-control.c
>> @@ -21,8 +21,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
>> TraceEventID id;
>> assert(trace_event_get_state_static(ev));
>> id = trace_event_get_id(ev);
>> -    trace_events_enabled_count += state - trace_events_dstate[id];
>> -    trace_events_dstate[id] = state;
>> +    if (state) {
>> +        trace_events_enabled_count++;
>> +        trace_events_dstate[id] = 1;
>> +    } else {
>> +        trace_events_enabled_count--;

> SHouldn't this be trace_events_enabled_count -= trace_events_dstate[id];
> as it is possible to call this method for a trace event that is a per-vcpu
> event

The "stub" code will never have vCPUs around, it's used by qemu-img and the like
(any program without "target" code).

I can send a v4 explicitly commenting that if you think that's necessary.


Thanks,
  Lluis

Re: [Qemu-devel] [PATCH v3 2/2] trace: Avoid implicit bool->integer conversions

[Daniel P. Berrange]

On Thu, Aug 11, 2016 at 06:41:36PM +0200, Lluís Vilanova wrote:
> Daniel P Berrange writes:
> 
> > On Thu, Aug 11, 2016 at 06:11:29PM +0200, Lluís Vilanova wrote:
> >> An explicit if/else is clearer than arithmetic assuming #true is 1,
> >> while the compiler should be able to generate just as optimal code.
> >> 
> >> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
> >> ---
> >> stubs/trace-control.c  |    9 +++++++--
> >> trace/control-target.c |   18 ++++++++++++++----
> >> 2 files changed, 21 insertions(+), 6 deletions(-)
> >> 
> >> diff --git a/stubs/trace-control.c b/stubs/trace-control.c
> >> index 3740c38..099c2b5 100644
> >> --- a/stubs/trace-control.c
> >> +++ b/stubs/trace-control.c
> >> @@ -21,8 +21,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
> >> TraceEventID id;
> >> assert(trace_event_get_state_static(ev));
> >> id = trace_event_get_id(ev);
> >> -    trace_events_enabled_count += state - trace_events_dstate[id];
> >> -    trace_events_dstate[id] = state;
> >> +    if (state) {
> >> +        trace_events_enabled_count++;
> >> +        trace_events_dstate[id] = 1;
> >> +    } else {
> >> +        trace_events_enabled_count--;
> 
> > SHouldn't this be trace_events_enabled_count -= trace_events_dstate[id];
> > as it is possible to call this method for a trace event that is a per-vcpu
> > event
> 
> The "stub" code will never have vCPUs around, it's used by qemu-img and the like
> (any program without "target" code).

I just picked the first example of that in this file - you've got the same
pattern in the other 2 places you change

Regards,
Daniel
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Re: [Qemu-devel] [PATCH v3 2/2] trace: Avoid implicit bool->integer conversions

[Lluís Vilanova]

Daniel P Berrange writes:

> On Thu, Aug 11, 2016 at 06:41:36PM +0200, Lluís Vilanova wrote:
>> Daniel P Berrange writes:
>> 
>> > On Thu, Aug 11, 2016 at 06:11:29PM +0200, Lluís Vilanova wrote:
>> >> An explicit if/else is clearer than arithmetic assuming #true is 1,
>> >> while the compiler should be able to generate just as optimal code.
>> >> 
>> >> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
>> >> ---
>> >> stubs/trace-control.c  |    9 +++++++--
>> >> trace/control-target.c |   18 ++++++++++++++----
>> >> 2 files changed, 21 insertions(+), 6 deletions(-)
>> >> 
>> >> diff --git a/stubs/trace-control.c b/stubs/trace-control.c
>> >> index 3740c38..099c2b5 100644
>> >> --- a/stubs/trace-control.c
>> >> +++ b/stubs/trace-control.c
>> >> @@ -21,8 +21,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool state)
>> >> TraceEventID id;
>> >> assert(trace_event_get_state_static(ev));
>> >> id = trace_event_get_id(ev);
>> >> -    trace_events_enabled_count += state - trace_events_dstate[id];
>> >> -    trace_events_dstate[id] = state;
>> >> +    if (state) {
>> >> +        trace_events_enabled_count++;
>> >> +        trace_events_dstate[id] = 1;
>> >> +    } else {
>> >> +        trace_events_enabled_count--;
>> 
>> > SHouldn't this be trace_events_enabled_count -= trace_events_dstate[id];
>> > as it is possible to call this method for a trace event that is a per-vcpu
>> > event
>> 
>> The "stub" code will never have vCPUs around, it's used by qemu-img and the like
>> (any program without "target" code).

> I just picked the first example of that in this file - you've got the same
> pattern in the other 2 places you change

In the "control-target.c" file, there's two places where this pattern also
appears.

In trace_event_set_state_dynamic(), the pattern only appears on events that do
*not* have the "vcpu" property, and so the counter is always either 1 or 0.

In trace_event_set_state_dynamic_init() there's the "special" case where we
assume there won't be multiple enables of a single event with "vcpu" (as the
comment says); this is what let's us get rid of the dstate_init array.

What I just saw is wrong is that this code looses the ability to make
enable/disable operations idempotent. I'll send a v4 with that fixed.


Thanks,
  Lluis