Improve a bit code readability.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qom/object_interfaces.h | 4 ++++
 qom/object.c                    | 4 ++--
 qom/object_interfaces.c         | 9 +++------
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
index 4d513fb329..46b0861457 100644
--- a/include/qom/object_interfaces.h
+++ b/include/qom/object_interfaces.h
@@ -9,9 +9,13 @@
 #define USER_CREATABLE_CLASS(klass) \
      OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
                         TYPE_USER_CREATABLE)
+#define IS_USER_CREATABLE_CLASS(klass) \
+    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
 #define USER_CREATABLE_GET_CLASS(obj) \
      OBJECT_GET_CLASS(UserCreatableClass, (obj), \
                       TYPE_USER_CREATABLE)
+#define IS_USER_CREATABLE(obj) \
+    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
 #define USER_CREATABLE(obj) \
      INTERFACE_CHECK(UserCreatable, (obj), \
                      TYPE_USER_CREATABLE)
diff --git a/qom/object.c b/qom/object.c
index 75d1d48944..0703e8e4ff 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
         goto out;
     }
 
-    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
+    if (IS_USER_CREATABLE(obj)) {
         user_creatable_complete(obj, &local_err);
         if (local_err) {
             object_unparent(obj);
@@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
         goto error;
     }
 
-    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
+    if (IS_USER_CREATABLE(obj)) {
         user_creatable_complete(obj, &local_err);
         if (local_err) {
             object_unparent(obj);
diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
index 72b97a8bed..e3084bc04a 100644
--- a/qom/object_interfaces.c
+++ b/qom/object_interfaces.c
@@ -10,18 +10,15 @@
 
 void user_creatable_complete(Object *obj, Error **errp)
 {
-
     UserCreatableClass *ucc;
-    UserCreatable *uc =
-        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
 
-    if (!uc) {
+    if (!IS_USER_CREATABLE(obj)) {
         return;
     }
 
-    ucc = USER_CREATABLE_GET_CLASS(uc);
+    ucc = USER_CREATABLE_GET_CLASS(obj);
     if (ucc->complete) {
-        ucc->complete(uc, errp);
+        ucc->complete(USER_CREATABLE(obj), errp);
     }
 }
 
-- 
2.19.0.rc1

On Wed, 12 Sep 2018 16:55:23 +0400
Marc-André Lureau <marcandre.lureau@redhat.com> wrote:

> Improve a bit code readability.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  include/qom/object_interfaces.h | 4 ++++
>  qom/object.c                    | 4 ++--
>  qom/object_interfaces.c         | 9 +++------
>  3 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> index 4d513fb329..46b0861457 100644
> --- a/include/qom/object_interfaces.h
> +++ b/include/qom/object_interfaces.h
> @@ -9,9 +9,13 @@
>  #define USER_CREATABLE_CLASS(klass) \
>       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
>                          TYPE_USER_CREATABLE)
> +#define IS_USER_CREATABLE_CLASS(klass) \
> +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
>  #define USER_CREATABLE_GET_CLASS(obj) \
>       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
>                        TYPE_USER_CREATABLE)
> +#define IS_USER_CREATABLE(obj) \
> +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
>  #define USER_CREATABLE(obj) \
>       INTERFACE_CHECK(UserCreatable, (obj), \
>                       TYPE_USER_CREATABLE)
> diff --git a/qom/object.c b/qom/object.c
> index 75d1d48944..0703e8e4ff 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
>          goto out;
>      }
>  
> -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> +    if (IS_USER_CREATABLE(obj)) {
>          user_creatable_complete(obj, &local_err);
>          if (local_err) {
>              object_unparent(obj);
> @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
>          goto error;
>      }
>  
> -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> +    if (IS_USER_CREATABLE(obj)) {
>          user_creatable_complete(obj, &local_err);
>          if (local_err) {
>              object_unparent(obj);
> diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> index 72b97a8bed..e3084bc04a 100644
> --- a/qom/object_interfaces.c
> +++ b/qom/object_interfaces.c
> @@ -10,18 +10,15 @@
>  
>  void user_creatable_complete(Object *obj, Error **errp)
>  {
> -
>      UserCreatableClass *ucc;
> -    UserCreatable *uc =
> -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
>  
> -    if (!uc) {
> +    if (!IS_USER_CREATABLE(obj)) {
>          return;
>      }
>  
> -    ucc = USER_CREATABLE_GET_CLASS(uc);
> +    ucc = USER_CREATABLE_GET_CLASS(obj);
>      if (ucc->complete) {
> -        ucc->complete(uc, errp);
> +        ucc->complete(USER_CREATABLE(obj), errp);
                         ^^^
even though function becomes more concise,
this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
so I'm not sure is a good idea to regress startup time for readability. 


>      }
>  }
>  

On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:
> On Wed, 12 Sep 2018 16:55:23 +0400
> Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> 
> > Improve a bit code readability.
> > 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  include/qom/object_interfaces.h | 4 ++++
> >  qom/object.c                    | 4 ++--
> >  qom/object_interfaces.c         | 9 +++------
> >  3 files changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > index 4d513fb329..46b0861457 100644
> > --- a/include/qom/object_interfaces.h
> > +++ b/include/qom/object_interfaces.h
> > @@ -9,9 +9,13 @@
> >  #define USER_CREATABLE_CLASS(klass) \
> >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> >                          TYPE_USER_CREATABLE)
> > +#define IS_USER_CREATABLE_CLASS(klass) \
> > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> >  #define USER_CREATABLE_GET_CLASS(obj) \
> >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> >                        TYPE_USER_CREATABLE)
> > +#define IS_USER_CREATABLE(obj) \
> > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> >  #define USER_CREATABLE(obj) \
> >       INTERFACE_CHECK(UserCreatable, (obj), \
> >                       TYPE_USER_CREATABLE)
> > diff --git a/qom/object.c b/qom/object.c
> > index 75d1d48944..0703e8e4ff 100644
> > --- a/qom/object.c
> > +++ b/qom/object.c
> > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> >          goto out;
> >      }
> >  
> > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > +    if (IS_USER_CREATABLE(obj)) {
> >          user_creatable_complete(obj, &local_err);
> >          if (local_err) {
> >              object_unparent(obj);
> > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> >          goto error;
> >      }
> >  
> > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > +    if (IS_USER_CREATABLE(obj)) {
> >          user_creatable_complete(obj, &local_err);
> >          if (local_err) {
> >              object_unparent(obj);
> > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > index 72b97a8bed..e3084bc04a 100644
> > --- a/qom/object_interfaces.c
> > +++ b/qom/object_interfaces.c
> > @@ -10,18 +10,15 @@
> >  
> >  void user_creatable_complete(Object *obj, Error **errp)
> >  {
> > -
> >      UserCreatableClass *ucc;
> > -    UserCreatable *uc =
> > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> >  
> > -    if (!uc) {
> > +    if (!IS_USER_CREATABLE(obj)) {
> >          return;
> >      }
> >  
> > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> >      if (ucc->complete) {
> > -        ucc->complete(uc, errp);
> > +        ucc->complete(USER_CREATABLE(obj), errp);
>                          ^^^
> even though function becomes more concise,
> this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> so I'm not sure is a good idea to regress startup time for readability. 

(INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
enabled, so I don't understand how it would regress startup time.

-- 
Eduardo

On Fri, 26 Oct 2018 12:13:21 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:
> > On Wed, 12 Sep 2018 16:55:23 +0400
> > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> >   
> > > Improve a bit code readability.
> > > 
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  include/qom/object_interfaces.h | 4 ++++
> > >  qom/object.c                    | 4 ++--
> > >  qom/object_interfaces.c         | 9 +++------
> > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > index 4d513fb329..46b0861457 100644
> > > --- a/include/qom/object_interfaces.h
> > > +++ b/include/qom/object_interfaces.h
> > > @@ -9,9 +9,13 @@
> > >  #define USER_CREATABLE_CLASS(klass) \
> > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > >                          TYPE_USER_CREATABLE)
> > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > >                        TYPE_USER_CREATABLE)
> > > +#define IS_USER_CREATABLE(obj) \
> > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > >  #define USER_CREATABLE(obj) \
> > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > >                       TYPE_USER_CREATABLE)
> > > diff --git a/qom/object.c b/qom/object.c
> > > index 75d1d48944..0703e8e4ff 100644
> > > --- a/qom/object.c
> > > +++ b/qom/object.c
> > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > >          goto out;
> > >      }
> > >  
> > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > +    if (IS_USER_CREATABLE(obj)) {
> > >          user_creatable_complete(obj, &local_err);
> > >          if (local_err) {
> > >              object_unparent(obj);
> > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > >          goto error;
> > >      }
> > >  
> > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > +    if (IS_USER_CREATABLE(obj)) {
> > >          user_creatable_complete(obj, &local_err);
> > >          if (local_err) {
> > >              object_unparent(obj);
> > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > index 72b97a8bed..e3084bc04a 100644
> > > --- a/qom/object_interfaces.c
> > > +++ b/qom/object_interfaces.c
> > > @@ -10,18 +10,15 @@
> > >  
> > >  void user_creatable_complete(Object *obj, Error **errp)
> > >  {
> > > -
> > >      UserCreatableClass *ucc;
> > > -    UserCreatable *uc =
> > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > >  
> > > -    if (!uc) {
> > > +    if (!IS_USER_CREATABLE(obj)) {
> > >          return;
> > >      }
> > >  
> > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > >      if (ucc->complete) {
> > > -        ucc->complete(uc, errp);
> > > +        ucc->complete(USER_CREATABLE(obj), errp);  
> >                          ^^^
> > even though function becomes more concise,
> > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > so I'm not sure is a good idea to regress startup time for readability.   
> 
> (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> enabled, so I don't understand how it would regress startup time.
Isn't it enabled by default though?
Maybe we should flip default to disabled then cast should be ok and enable it
when generic '--debug' is enabled.

On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:
> On Fri, 26 Oct 2018 12:13:21 -0300
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:
> > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > >   
> > > > Improve a bit code readability.
> > > > 
> > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > ---
> > > >  include/qom/object_interfaces.h | 4 ++++
> > > >  qom/object.c                    | 4 ++--
> > > >  qom/object_interfaces.c         | 9 +++------
> > > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > > 
> > > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > > index 4d513fb329..46b0861457 100644
> > > > --- a/include/qom/object_interfaces.h
> > > > +++ b/include/qom/object_interfaces.h
> > > > @@ -9,9 +9,13 @@
> > > >  #define USER_CREATABLE_CLASS(klass) \
> > > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > > >                          TYPE_USER_CREATABLE)
> > > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > > >                        TYPE_USER_CREATABLE)
> > > > +#define IS_USER_CREATABLE(obj) \
> > > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > > >  #define USER_CREATABLE(obj) \
> > > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > > >                       TYPE_USER_CREATABLE)
> > > > diff --git a/qom/object.c b/qom/object.c
> > > > index 75d1d48944..0703e8e4ff 100644
> > > > --- a/qom/object.c
> > > > +++ b/qom/object.c
> > > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > > >          goto out;
> > > >      }
> > > >  
> > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > +    if (IS_USER_CREATABLE(obj)) {
> > > >          user_creatable_complete(obj, &local_err);
> > > >          if (local_err) {
> > > >              object_unparent(obj);
> > > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > > >          goto error;
> > > >      }
> > > >  
> > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > +    if (IS_USER_CREATABLE(obj)) {
> > > >          user_creatable_complete(obj, &local_err);
> > > >          if (local_err) {
> > > >              object_unparent(obj);
> > > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > > index 72b97a8bed..e3084bc04a 100644
> > > > --- a/qom/object_interfaces.c
> > > > +++ b/qom/object_interfaces.c
> > > > @@ -10,18 +10,15 @@
> > > >  
> > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > >  {
> > > > -
> > > >      UserCreatableClass *ucc;
> > > > -    UserCreatable *uc =
> > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > >  
> > > > -    if (!uc) {
> > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > >          return;
> > > >      }
> > > >  
> > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > >      if (ucc->complete) {
> > > > -        ucc->complete(uc, errp);
> > > > +        ucc->complete(USER_CREATABLE(obj), errp);  
> > >                          ^^^
> > > even though function becomes more concise,
> > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > so I'm not sure is a good idea to regress startup time for readability.   
> > 
> > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> > enabled, so I don't understand how it would regress startup time.
> Isn't it enabled by default though?
> Maybe we should flip default to disabled then cast should be ok and enable it
> when generic '--debug' is enabled.

This is called only once for each -object option.  Even if QOM
debugging is enabled by default I don't see why it wouldn't be OK
to call object_dynamic_cast_assert() here.

-- 
Eduardo

Hi

On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
>
> On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:
> > On Fri, 26 Oct 2018 12:13:21 -0300
> > Eduardo Habkost <ehabkost@redhat.com> wrote:
> >
> > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:
> > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > > >
> > > > > Improve a bit code readability.
> > > > >
> > > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > > ---
> > > > >  include/qom/object_interfaces.h | 4 ++++
> > > > >  qom/object.c                    | 4 ++--
> > > > >  qom/object_interfaces.c         | 9 +++------
> > > > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > > >
> > > > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > > > index 4d513fb329..46b0861457 100644
> > > > > --- a/include/qom/object_interfaces.h
> > > > > +++ b/include/qom/object_interfaces.h
> > > > > @@ -9,9 +9,13 @@
> > > > >  #define USER_CREATABLE_CLASS(klass) \
> > > > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > > > >                          TYPE_USER_CREATABLE)
> > > > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > > > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > > > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > > > >                        TYPE_USER_CREATABLE)
> > > > > +#define IS_USER_CREATABLE(obj) \
> > > > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > > > >  #define USER_CREATABLE(obj) \
> > > > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > > > >                       TYPE_USER_CREATABLE)
> > > > > diff --git a/qom/object.c b/qom/object.c
> > > > > index 75d1d48944..0703e8e4ff 100644
> > > > > --- a/qom/object.c
> > > > > +++ b/qom/object.c
> > > > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > > > >          goto out;
> > > > >      }
> > > > >
> > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > >          user_creatable_complete(obj, &local_err);
> > > > >          if (local_err) {
> > > > >              object_unparent(obj);
> > > > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > > > >          goto error;
> > > > >      }
> > > > >
> > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > >          user_creatable_complete(obj, &local_err);
> > > > >          if (local_err) {
> > > > >              object_unparent(obj);
> > > > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > > > index 72b97a8bed..e3084bc04a 100644
> > > > > --- a/qom/object_interfaces.c
> > > > > +++ b/qom/object_interfaces.c
> > > > > @@ -10,18 +10,15 @@
> > > > >
> > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > >  {
> > > > > -
> > > > >      UserCreatableClass *ucc;
> > > > > -    UserCreatable *uc =
> > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > >
> > > > > -    if (!uc) {
> > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > >          return;
> > > > >      }
> > > > >
> > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > >      if (ucc->complete) {
> > > > > -        ucc->complete(uc, errp);
> > > > > +        ucc->complete(USER_CREATABLE(obj), errp);
> > > >                          ^^^
> > > > even though function becomes more concise,
> > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > so I'm not sure is a good idea to regress startup time for readability.

I hope it's not measurable, unless we create billions of objects. Do
you want some figures?

> > >
> > > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> > > enabled, so I don't understand how it would regress startup time.
> > Isn't it enabled by default though?
> > Maybe we should flip default to disabled then cast should be ok and enable it
> > when generic '--debug' is enabled.
>
> This is called only once for each -object option.  Even if QOM
> debugging is enabled by default I don't see why it wouldn't be OK
> to call object_dynamic_cast_assert() here.

Yes, imho it's very marginal. Thus I would value more readability.

Alternatively, we can consider replacing
ucc->complete(USER_CREATABLE(obj), errp); by
ucc->complete((UserCreatable*)obj, errp); to get back to the same
number of dynamic_cast calls.

On Tue, 30 Oct 2018 13:26:40 +0400
Marc-André Lureau <marcandre.lureau@redhat.com> wrote:

> Hi
> 
> On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
> >
> > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:  
> > > On Fri, 26 Oct 2018 12:13:21 -0300
> > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > >  
> > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:  
> > > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > > > >  
> > > > > > Improve a bit code readability.
> > > > > >
> > > > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > > > ---
> > > > > >  include/qom/object_interfaces.h | 4 ++++
> > > > > >  qom/object.c                    | 4 ++--
> > > > > >  qom/object_interfaces.c         | 9 +++------
> > > > > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > > > >
> > > > > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > > > > index 4d513fb329..46b0861457 100644
> > > > > > --- a/include/qom/object_interfaces.h
> > > > > > +++ b/include/qom/object_interfaces.h
> > > > > > @@ -9,9 +9,13 @@
> > > > > >  #define USER_CREATABLE_CLASS(klass) \
> > > > > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > > > > >                          TYPE_USER_CREATABLE)
> > > > > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > > > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > > > > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > > > > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > > > > >                        TYPE_USER_CREATABLE)
> > > > > > +#define IS_USER_CREATABLE(obj) \
> > > > > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > > > > >  #define USER_CREATABLE(obj) \
> > > > > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > > > > >                       TYPE_USER_CREATABLE)
> > > > > > diff --git a/qom/object.c b/qom/object.c
> > > > > > index 75d1d48944..0703e8e4ff 100644
> > > > > > --- a/qom/object.c
> > > > > > +++ b/qom/object.c
> > > > > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > > > > >          goto out;
> > > > > >      }
> > > > > >
> > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > >          user_creatable_complete(obj, &local_err);
> > > > > >          if (local_err) {
> > > > > >              object_unparent(obj);
> > > > > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > > > > >          goto error;
> > > > > >      }
> > > > > >
> > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > >          user_creatable_complete(obj, &local_err);
> > > > > >          if (local_err) {
> > > > > >              object_unparent(obj);
> > > > > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > > > > index 72b97a8bed..e3084bc04a 100644
> > > > > > --- a/qom/object_interfaces.c
> > > > > > +++ b/qom/object_interfaces.c
> > > > > > @@ -10,18 +10,15 @@
> > > > > >
> > > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > > >  {
> > > > > > -
> > > > > >      UserCreatableClass *ucc;
> > > > > > -    UserCreatable *uc =
> > > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > > >
> > > > > > -    if (!uc) {
> > > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > > >          return;
> > > > > >      }
> > > > > >
> > > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > > >      if (ucc->complete) {
> > > > > > -        ucc->complete(uc, errp);
> > > > > > +        ucc->complete(USER_CREATABLE(obj), errp);  
> > > > >                          ^^^
> > > > > even though function becomes more concise,
> > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > > so I'm not sure is a good idea to regress startup time for readability.  
> 
> I hope it's not measurable, unless we create billions of objects. Do
> you want some figures?
I recall penalty was big enough for QEMU, that we added qom debug option,
in case of -object, the cost could be multiplied by hundreds


> > > > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> > > > enabled, so I don't understand how it would regress startup time.  
> > > Isn't it enabled by default though?
> > > Maybe we should flip default to disabled then cast should be ok and enable it
> > > when generic '--debug' is enabled.  
> >
> > This is called only once for each -object option.  Even if QOM
> > debugging is enabled by default I don't see why it wouldn't be OK
> > to call object_dynamic_cast_assert() here.  
> 
> Yes, imho it's very marginal. Thus I would value more readability.
Probably not marginal for folks who are trying to reduce every
tiny bit of start up time.

Considering readablity change here doesn't really make a difference,
I'd pick performance. i.e. do cast and then reuse result later.
 
> Alternatively, we can consider replacing
> ucc->complete(USER_CREATABLE(obj), errp); by
> ucc->complete((UserCreatable*)obj, errp); to get back to the same
> number of dynamic_cast calls.
Unsafe casts (foo*) typically frowned upon but it should be safe
since one gets here after IS_USER_CREATABLE check, so I don't really
care in this case. But I'd drop user_creatable_complete() hunk,
so that original cast result is being reused.

On Tue, Oct 30, 2018 at 03:22:43PM +0100, Igor Mammedov wrote:
> On Tue, 30 Oct 2018 13:26:40 +0400
> Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> 
> > Hi
> > 
> > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
> > >
> > > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:  
> > > > On Fri, 26 Oct 2018 12:13:21 -0300
> > > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > >  
> > > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:  
> > > > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > > > > >  
> > > > > > > Improve a bit code readability.
> > > > > > >
> > > > > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > > > > ---
> > > > > > >  include/qom/object_interfaces.h | 4 ++++
> > > > > > >  qom/object.c                    | 4 ++--
> > > > > > >  qom/object_interfaces.c         | 9 +++------
> > > > > > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > > > > >
> > > > > > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > > > > > index 4d513fb329..46b0861457 100644
> > > > > > > --- a/include/qom/object_interfaces.h
> > > > > > > +++ b/include/qom/object_interfaces.h
> > > > > > > @@ -9,9 +9,13 @@
> > > > > > >  #define USER_CREATABLE_CLASS(klass) \
> > > > > > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > > > > > >                          TYPE_USER_CREATABLE)
> > > > > > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > > > > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > > > > > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > > > > > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > > > > > >                        TYPE_USER_CREATABLE)
> > > > > > > +#define IS_USER_CREATABLE(obj) \
> > > > > > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > > > > > >  #define USER_CREATABLE(obj) \
> > > > > > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > > > > > >                       TYPE_USER_CREATABLE)
> > > > > > > diff --git a/qom/object.c b/qom/object.c
> > > > > > > index 75d1d48944..0703e8e4ff 100644
> > > > > > > --- a/qom/object.c
> > > > > > > +++ b/qom/object.c
> > > > > > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > > > > > >          goto out;
> > > > > > >      }
> > > > > > >
> > > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > > >          user_creatable_complete(obj, &local_err);
> > > > > > >          if (local_err) {
> > > > > > >              object_unparent(obj);
> > > > > > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > > > > > >          goto error;
> > > > > > >      }
> > > > > > >
> > > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > > >          user_creatable_complete(obj, &local_err);
> > > > > > >          if (local_err) {
> > > > > > >              object_unparent(obj);
> > > > > > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > > > > > index 72b97a8bed..e3084bc04a 100644
> > > > > > > --- a/qom/object_interfaces.c
> > > > > > > +++ b/qom/object_interfaces.c
> > > > > > > @@ -10,18 +10,15 @@
> > > > > > >
> > > > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > > > >  {
> > > > > > > -
> > > > > > >      UserCreatableClass *ucc;
> > > > > > > -    UserCreatable *uc =
> > > > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > > > >
> > > > > > > -    if (!uc) {
> > > > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > > > >          return;
> > > > > > >      }
> > > > > > >
> > > > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > > > >      if (ucc->complete) {
> > > > > > > -        ucc->complete(uc, errp);
> > > > > > > +        ucc->complete(USER_CREATABLE(obj), errp);  
> > > > > >                          ^^^
> > > > > > even though function becomes more concise,
> > > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > > > so I'm not sure is a good idea to regress startup time for readability.  
> > 
> > I hope it's not measurable, unless we create billions of objects. Do
> > you want some figures?
> I recall penalty was big enough for QEMU, that we added qom debug option,
> in case of -object, the cost could be multiplied by hundreds

This sounds like premature optimization.  Did you measure how
many nanoseconds we're saving per -object option?


> > > > > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> > > > > enabled, so I don't understand how it would regress startup time.  
> > > > Isn't it enabled by default though?
> > > > Maybe we should flip default to disabled then cast should be ok and enable it
> > > > when generic '--debug' is enabled.  
> > >
> > > This is called only once for each -object option.  Even if QOM
> > > debugging is enabled by default I don't see why it wouldn't be OK
> > > to call object_dynamic_cast_assert() here.  
> > 
> > Yes, imho it's very marginal. Thus I would value more readability.
> Probably not marginal for folks who are trying to reduce every
> tiny bit of start up time.

These people should be disabling QOM debugging, then.

> 
> Considering readablity change here doesn't really make a difference,
> I'd pick performance. i.e. do cast and then reuse result later.
>  
> > Alternatively, we can consider replacing
> > ucc->complete(USER_CREATABLE(obj), errp); by
> > ucc->complete((UserCreatable*)obj, errp); to get back to the same
> > number of dynamic_cast calls.
> Unsafe casts (foo*) typically frowned upon but it should be safe
> since one gets here after IS_USER_CREATABLE check, so I don't really
> care in this case. But I'd drop user_creatable_complete() hunk,
> so that original cast result is being reused.

Please don't do that.  Readability, safety, and consistency are
more important.  For the few users where QOM debugging has a
measurable performance impact, we already have a mechanism to
disable it.

-- 
Eduardo

On Tue, 30 Oct 2018 20:07:17 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Tue, Oct 30, 2018 at 03:22:43PM +0100, Igor Mammedov wrote:
> > On Tue, 30 Oct 2018 13:26:40 +0400
> > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> >   
> > > Hi
> > > 
> > > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:  
> > > >
> > > > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:    
> > > > > On Fri, 26 Oct 2018 12:13:21 -0300
> > > > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > > >    
> > > > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:    
> > > > > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > > > > > >    
> > > > > > > > Improve a bit code readability.
> > > > > > > >
> > > > > > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > > > > > ---
> > > > > > > >  include/qom/object_interfaces.h | 4 ++++
> > > > > > > >  qom/object.c                    | 4 ++--
> > > > > > > >  qom/object_interfaces.c         | 9 +++------
> > > > > > > >  3 files changed, 9 insertions(+), 8 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/include/qom/object_interfaces.h b/include/qom/object_interfaces.h
> > > > > > > > index 4d513fb329..46b0861457 100644
> > > > > > > > --- a/include/qom/object_interfaces.h
> > > > > > > > +++ b/include/qom/object_interfaces.h
> > > > > > > > @@ -9,9 +9,13 @@
> > > > > > > >  #define USER_CREATABLE_CLASS(klass) \
> > > > > > > >       OBJECT_CLASS_CHECK(UserCreatableClass, (klass), \
> > > > > > > >                          TYPE_USER_CREATABLE)
> > > > > > > > +#define IS_USER_CREATABLE_CLASS(klass) \
> > > > > > > > +    object_class_dynamic_cast(OBJECT_CLASS(oc), TYPE_USER_CREATABLE)
> > > > > > > >  #define USER_CREATABLE_GET_CLASS(obj) \
> > > > > > > >       OBJECT_GET_CLASS(UserCreatableClass, (obj), \
> > > > > > > >                        TYPE_USER_CREATABLE)
> > > > > > > > +#define IS_USER_CREATABLE(obj) \
> > > > > > > > +    object_dynamic_cast(OBJECT(obj), TYPE_USER_CREATABLE)
> > > > > > > >  #define USER_CREATABLE(obj) \
> > > > > > > >       INTERFACE_CHECK(UserCreatable, (obj), \
> > > > > > > >                       TYPE_USER_CREATABLE)
> > > > > > > > diff --git a/qom/object.c b/qom/object.c
> > > > > > > > index 75d1d48944..0703e8e4ff 100644
> > > > > > > > --- a/qom/object.c
> > > > > > > > +++ b/qom/object.c
> > > > > > > > @@ -424,7 +424,7 @@ void object_initialize_childv(Object *parentobj, const char *propname,
> > > > > > > >          goto out;
> > > > > > > >      }
> > > > > > > >
> > > > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > > > >          user_creatable_complete(obj, &local_err);
> > > > > > > >          if (local_err) {
> > > > > > > >              object_unparent(obj);
> > > > > > > > @@ -605,7 +605,7 @@ Object *object_new_with_propv(const char *typename,
> > > > > > > >          goto error;
> > > > > > > >      }
> > > > > > > >
> > > > > > > > -    if (object_dynamic_cast(obj, TYPE_USER_CREATABLE)) {
> > > > > > > > +    if (IS_USER_CREATABLE(obj)) {
> > > > > > > >          user_creatable_complete(obj, &local_err);
> > > > > > > >          if (local_err) {
> > > > > > > >              object_unparent(obj);
> > > > > > > > diff --git a/qom/object_interfaces.c b/qom/object_interfaces.c
> > > > > > > > index 72b97a8bed..e3084bc04a 100644
> > > > > > > > --- a/qom/object_interfaces.c
> > > > > > > > +++ b/qom/object_interfaces.c
> > > > > > > > @@ -10,18 +10,15 @@
> > > > > > > >
> > > > > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > > > > >  {
> > > > > > > > -
> > > > > > > >      UserCreatableClass *ucc;
> > > > > > > > -    UserCreatable *uc =
> > > > > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > > > > >
> > > > > > > > -    if (!uc) {
> > > > > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > > > > >          return;
> > > > > > > >      }
> > > > > > > >
> > > > > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > > > > >      if (ucc->complete) {
> > > > > > > > -        ucc->complete(uc, errp);
> > > > > > > > +        ucc->complete(USER_CREATABLE(obj), errp);    
> > > > > > >                          ^^^
> > > > > > > even though function becomes more concise,
> > > > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > > > > so I'm not sure is a good idea to regress startup time for readability.    
> > > 
> > > I hope it's not measurable, unless we create billions of objects. Do
> > > you want some figures?  
> > I recall penalty was big enough for QEMU, that we added qom debug option,
> > in case of -object, the cost could be multiplied by hundreds  
> 
> This sounds like premature optimization.  Did you measure how
> many nanoseconds we're saving per -object option?
it's not optimization, it's about not making code worse and using
resources reasonably object_dynamic_cast() with IS_USER_CREATABLE().

I'd replace object_dynamic_cast() with IS_FOO() in places where
we just test but do not use the result for a better readability.
But is we need the result later I'd keep object_dynamic_cast(),
it's not much worse but allows us to reuse the result of cast.
 
> > > > > > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not
> > > > > > enabled, so I don't understand how it would regress startup time.    
> > > > > Isn't it enabled by default though?
> > > > > Maybe we should flip default to disabled then cast should be ok and enable it
> > > > > when generic '--debug' is enabled.    
> > > >
> > > > This is called only once for each -object option.  Even if QOM
> > > > debugging is enabled by default I don't see why it wouldn't be OK
> > > > to call object_dynamic_cast_assert() here.    
> > > 
> > > Yes, imho it's very marginal. Thus I would value more readability.  
> > Probably not marginal for folks who are trying to reduce every
> > tiny bit of start up time.  
> 
> These people should be disabling QOM debugging, then.
> 
> > 
> > Considering readablity change here doesn't really make a difference,
> > I'd pick performance. i.e. do cast and then reuse result later.
> >    
> > > Alternatively, we can consider replacing
> > > ucc->complete(USER_CREATABLE(obj), errp); by
> > > ucc->complete((UserCreatable*)obj, errp); to get back to the same
> > > number of dynamic_cast calls.  
> > Unsafe casts (foo*) typically frowned upon but it should be safe
> > since one gets here after IS_USER_CREATABLE check, so I don't really
> > care in this case. But I'd drop user_creatable_complete() hunk,
> > so that original cast result is being reused.  
> 
> Please don't do that.  Readability, safety, and consistency are
> more important.  For the few users where QOM debugging has a
> measurable performance impact, we already have a mechanism to
> disable it.

On Thu, Nov 01, 2018 at 01:16:37PM +0100, Igor Mammedov wrote:
> On Tue, 30 Oct 2018 20:07:17 -0300
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Tue, Oct 30, 2018 at 03:22:43PM +0100, Igor Mammedov wrote:
> > > On Tue, 30 Oct 2018 13:26:40 +0400
> > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > >   
> > > > Hi
> > > > 
> > > > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:  
> > > > >
> > > > > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:    
> > > > > > On Fri, 26 Oct 2018 12:13:21 -0300
> > > > > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > > > >    
> > > > > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:    
> > > > > > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > > > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
[...]
> > > > > > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > > > > > >  {
> > > > > > > > > -
> > > > > > > > >      UserCreatableClass *ucc;
> > > > > > > > > -    UserCreatable *uc =
> > > > > > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > > > > > >
> > > > > > > > > -    if (!uc) {
> > > > > > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > > > > > >          return;
> > > > > > > > >      }
> > > > > > > > >
> > > > > > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > > > > > >      if (ucc->complete) {
> > > > > > > > > -        ucc->complete(uc, errp);
> > > > > > > > > +        ucc->complete(USER_CREATABLE(obj), errp);    
> > > > > > > >                          ^^^
> > > > > > > > even though function becomes more concise,
> > > > > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > > > > > so I'm not sure is a good idea to regress startup time for readability.    
> > > > 
> > > > I hope it's not measurable, unless we create billions of objects. Do
> > > > you want some figures?  
> > > I recall penalty was big enough for QEMU, that we added qom debug option,
> > > in case of -object, the cost could be multiplied by hundreds  
> > 
> > This sounds like premature optimization.  Did you measure how
> > many nanoseconds we're saving per -object option?
> it's not optimization, it's about not making code worse and using
> resources reasonably object_dynamic_cast() with IS_USER_CREATABLE().

How exactly is the code worse?

> 
> I'd replace object_dynamic_cast() with IS_FOO() in places where
> we just test but do not use the result for a better readability.
> But is we need the result later I'd keep object_dynamic_cast(),
> it's not much worse but allows us to reuse the result of cast.

Readability is orders of magnitude more important to me.

This is not readable:
  (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE)

This is readable:
  USER_CREATABLE(obj)

If the overhead of the extra object_dynamic_cast() call is too
much, it's already possible to disable QOM cast debugging.

> [...]

-- 
Eduardo

On Thu, 1 Nov 2018 12:02:03 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Thu, Nov 01, 2018 at 01:16:37PM +0100, Igor Mammedov wrote:
> > On Tue, 30 Oct 2018 20:07:17 -0300
> > Eduardo Habkost <ehabkost@redhat.com> wrote:
> >   
> > > On Tue, Oct 30, 2018 at 03:22:43PM +0100, Igor Mammedov wrote:  
> > > > On Tue, 30 Oct 2018 13:26:40 +0400
> > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> > > >     
> > > > > Hi
> > > > > 
> > > > > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabkost@redhat.com> wrote:    
> > > > > >
> > > > > > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote:      
> > > > > > > On Fri, 26 Oct 2018 12:13:21 -0300
> > > > > > > Eduardo Habkost <ehabkost@redhat.com> wrote:
> > > > > > >      
> > > > > > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote:      
> > > > > > > > > On Wed, 12 Sep 2018 16:55:23 +0400
> > > > > > > > > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:  
> [...]
> > > > > > > > > >  void user_creatable_complete(Object *obj, Error **errp)
> > > > > > > > > >  {
> > > > > > > > > > -
> > > > > > > > > >      UserCreatableClass *ucc;
> > > > > > > > > > -    UserCreatable *uc =
> > > > > > > > > > -        (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE);
> > > > > > > > > >
> > > > > > > > > > -    if (!uc) {
> > > > > > > > > > +    if (!IS_USER_CREATABLE(obj)) {
> > > > > > > > > >          return;
> > > > > > > > > >      }
> > > > > > > > > >
> > > > > > > > > > -    ucc = USER_CREATABLE_GET_CLASS(uc);
> > > > > > > > > > +    ucc = USER_CREATABLE_GET_CLASS(obj);
> > > > > > > > > >      if (ucc->complete) {
> > > > > > > > > > -        ucc->complete(uc, errp);
> > > > > > > > > > +        ucc->complete(USER_CREATABLE(obj), errp);      
> > > > > > > > >                          ^^^
> > > > > > > > > even though function becomes more concise,
> > > > > > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREATABLE was the 1st and discarded)
> > > > > > > > > so I'm not sure is a good idea to regress startup time for readability.      
> > > > > 
> > > > > I hope it's not measurable, unless we create billions of objects. Do
> > > > > you want some figures?    
> > > > I recall penalty was big enough for QEMU, that we added qom debug option,
> > > > in case of -object, the cost could be multiplied by hundreds    
> > > 
> > > This sounds like premature optimization.  Did you measure how
> > > many nanoseconds we're saving per -object option?  
> > it's not optimization, it's about not making code worse and using
> > resources reasonably object_dynamic_cast() with IS_USER_CREATABLE().  
> 
> How exactly is the code worse?
making it slower /doesn't matter how much/ when there is better way
to do it.
Anyways the point is moot as Mark rewrote it in another way (better)
so this question won't arise.

 
> > 
> > I'd replace object_dynamic_cast() with IS_FOO() in places where
> > we just test but do not use the result for a better readability.
> > But is we need the result later I'd keep object_dynamic_cast(),
> > it's not much worse but allows us to reuse the result of cast.  
> 
> Readability is orders of magnitude more important to me.
> 
> This is not readable:
>   (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE)
> 
> This is readable:
>   USER_CREATABLE(obj)
> 
> If the overhead of the extra object_dynamic_cast() call is too
> much, it's already possible to disable QOM cast debugging.

I'm typically on the side of simplifying code and readability
but in this case I have to disagree, out of context ^^^ it might
look fine but with full context

 uc = (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CREATABLE)
 if(uc)
    call(uc)

vs

 if(IS_USER_CREATABLE(obj))
   // discard above hidden cast result and do it again
   call(USER_CREATABLE(obj))
  
the former is not horrible enough to warrant doing senseless discard.
So lets agree to disagree :)

> 
> > [...]  
>