From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40811) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gHUv5-0002JU-NF for qemu-devel@nongnu.org; Tue, 30 Oct 2018 10:23:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gHUv1-0006KS-Mq for qemu-devel@nongnu.org; Tue, 30 Oct 2018 10:22:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50156) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gHUv1-0006Jg-EZ for qemu-devel@nongnu.org; Tue, 30 Oct 2018 10:22:55 -0400 Date: Tue, 30 Oct 2018 15:22:43 +0100 From: Igor Mammedov Message-ID: <20181030152243.1602e9d2@redhat.com> In-Reply-To: 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> 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: =?UTF-8?B?TWFyYy1BbmRyw6k=?= Lureau Cc: Eduardo Habkost , 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 13:26:40 +0400 Marc-Andr=C3=A9 Lureau wrote: > Hi >=20 > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost wro= te: > > > > 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/obje= ct_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_CREA= TABLE) > > > > > > #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 *paren= tobj, 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 *t= ypename, > > > > > > 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 =3D > > > > > > - (UserCreatable *)object_dynamic_cast(obj, TYPE_USER_CR= EATABLE); > > > > > > > > > > > > - 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_CREATABLE= was the 1st and discarded) > > > > > so I'm not sure is a good idea to regress startup time for readab= ility. =20 >=20 > 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. = =20 > > > Isn't it enabled by default though? > > > Maybe we should flip default to disabled then cast should be ok and e= nable 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. 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. =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. 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.