On Thu, Nov 01, 2018 at 01:16:37PM +0100, Igor Mammedov wrote: > On Tue, 30 Oct 2018 20:07:17 -0300 > Eduardo Habkost <ehabk...@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.lur...@redhat.com> wrote: > > > > > > > Hi > > > > > > > > On Tue, Oct 30, 2018 at 5:37 AM Eduardo Habkost <ehabk...@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 <ehabk...@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.lur...@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