From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35076) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gIC9j-0002UQ-8O for qemu-devel@nongnu.org; Thu, 01 Nov 2018 08:33:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gIBty-0006KT-NE for qemu-devel@nongnu.org; Thu, 01 Nov 2018 08:16:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63881) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gIBty-0006KB-Dj for qemu-devel@nongnu.org; Thu, 01 Nov 2018 08:16:42 -0400 Date: Thu, 1 Nov 2018 13:16:37 +0100 From: Igor Mammedov Message-ID: <20181101131637.5336779c@redhat.com> In-Reply-To: <20181030230717.GX3902@habkost.net> References: <20180912125531.32131-1-marcandre.lureau@redhat.com> <20180912125531.32131-2-marcandre.lureau@redhat.com> <20181022153330.6996de15@igors-macbook-pro.local> <20181026151321.GE3902@habkost.net> <20181029105657.5106265f@redhat.com> <20181030013702.GQ3902@habkost.net> <20181030152243.1602e9d2@redhat.com> <20181030230717.GX3902@habkost.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 1/9] qom/user-creatable: add a few helper macros List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: =?UTF-8?B?TWFyYy1BbmRyw6k=?= Lureau , qemu-devel , "Bonzini, Paolo" , Marcel Apfelbaum , "Dr. David Alan Gilbert" , Richard Henderson , Andreas =?UTF-8?B?RsOkcmJlcg==?= , "Michael S . Tsirkin" , atar4qemu@gmail.com, mark.cave-ayland@ilande.co.uk On Tue, 30 Oct 2018 20:07:17 -0300 Eduardo Habkost wrote: > On Tue, Oct 30, 2018 at 03:22:43PM +0100, Igor Mammedov wrote: > > On Tue, 30 Oct 2018 13:26:40 +0400 > > Marc-Andr=C3=A9 Lureau wrote: > > =20 > > > Hi > > >=20 > > > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost = wrote: =20 > > > > > > > > On Mon, Oct 29, 2018 at 10:56:57AM +0100, Igor Mammedov wrote: =20 > > > > > On Fri, 26 Oct 2018 12:13:21 -0300 > > > > > Eduardo Habkost wrote: > > > > > =20 > > > > > > On Mon, Oct 22, 2018 at 03:33:30PM +0100, Igor Mammedov wrote: = =20 > > > > > > > On Wed, 12 Sep 2018 16:55:23 +0400 > > > > > > > Marc-Andr=C3=A9 Lureau wrote: > > > > > > > =20 > > > > > > > > Improve a bit code readability. > > > > > > > > > > > > > > > > Signed-off-by: Marc-Andr=C3=A9 Lureau > > > > > > > > --- > > > > > > > > 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 *p= arentobj, 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 cha= r *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_interface= s.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 =3D > > > > > > > > - (UserCreatable *)object_dynamic_cast(obj, TYPE_USE= R_CREATABLE); > > > > > > > > > > > > > > > > - if (!uc) { > > > > > > > > + if (!IS_USER_CREATABLE(obj)) { > > > > > > > > return; > > > > > > > > } > > > > > > > > > > > > > > > > - ucc =3D USER_CREATABLE_GET_CLASS(uc); > > > > > > > > + ucc =3D USER_CREATABLE_GET_CLASS(obj); > > > > > > > > if (ucc->complete) { > > > > > > > > - ucc->complete(uc, errp); > > > > > > > > + ucc->complete(USER_CREATABLE(obj), errp); =20 > > > > > > > ^^^ > > > > > > > even though function becomes more concise, > > > > > > > this will call expensive dynamic cast 2nd time (IS_USER_CREAT= ABLE was the 1st and discarded) > > > > > > > so I'm not sure is a good idea to regress startup time for re= adability. =20 > > >=20 > > > I hope it's not measurable, unless we create billions of objects. Do > > > you want some figures? =20 > > I recall penalty was big enough for QEMU, that we added qom debug optio= n, > > in case of -object, the cost could be multiplied by hundreds =20 >=20 > 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. =20 > > > > > > (INTERFACE_CHECK is a nop if CONFIG_QOM_CAST_DEBUG is not > > > > > > enabled, so I don't understand how it would regress startup tim= e. =20 > > > > > Isn't it enabled by default though? > > > > > Maybe we should flip default to disabled then cast should be ok a= nd enable it > > > > > when generic '--debug' is enabled. =20 > > > > > > > > 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. =20 > > >=20 > > > Yes, imho it's very marginal. Thus I would value more readability. =20 > > Probably not marginal for folks who are trying to reduce every > > tiny bit of start up time. =20 >=20 > These people should be disabling QOM debugging, then. >=20 > >=20 > > Considering readablity change here doesn't really make a difference, > > I'd pick performance. i.e. do cast and then reuse result later. > > =20 > > > 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. =20 > > 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. =20 >=20 > 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.