Re: avoiding relocations in type registration

[Tim Janik <timj imendio com>]

On Mon, 3 Apr 2006, Matthias Clasen wrote:

> Sorry mitch, forgot to cc you. Here is mail I sent to Tim.
>
>
> Hey Tim,
>
> we discussed this on irc a bit, the static const GTypeInfo structs used
> for g_type_register_static cause quite a few relocations, and also, in
> 90% of the cases, most of the structs is always the same. The cost of
> relocations can in most cases alleviated by prelink (though
> LD_DEBUG=statistics shows me that prelink is not as reliable as one
> might hope, at least on ix86. Jakub tells me this is due to the kernel
> mapping the vDSO in an area that conflicts with prelinked libraries...).
>
> Here is a proposal to avoid the use of a static const struct (see the
> attached patch):
>
> GType
> g_type_register_static_simple (GType             parent_type,
> 			       const gchar      *type_name,
>                               guint16           class_size,

can you make this a guint instead?

>                               GClassInitFunc    class_init,
>                               guint16           instance_size,

and this? i don't think restricting to guint16 here really buys us anything.

>                               GInstanceInitFunc instance_init,
>                               GTypeFlags        flags);
>
>
> The current trivial implementation fills a GTypeInfo struct on the
> stack, but it should be possible to avoid the use of a struct
> altogether.

you mean inside g_type_register_static_simple? i don't see what's
wrong with the way you did it, i'd leave it as that.

> When doing this conversion for a single type in GTK+,
> I see .text grow by 16 bytes, while .data shrinks by 62, so it
> should be an overall win.

yeah, considerably even since .text is ro and shared.
thanks Matthias, can you commit this please? provided
it's properly tested.

> Matthias

---
ciaoTJ