On Fri, May 10, 2013 at 01:47:55PM -0500, Anthony Liguori wrote:
> Most QOM types use type_register_static but we still strdup the
> passed data. However, the original pointers are useful because
> GCC is pretty good about collapsing strings so its very likely any
> use of the pointer will end up being that same address.
>
> IOW, with a little trickery, we can compare types by just comparing
> strings and in fact that's what we do here.
>
> We do this for the two most common cases, casting to a leaf class
> or to the parent class.
>
> With these two changes, I see a decrease from around 2 hash table
> lookups to only a thousand with no run time lookups at all.
>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Aurelien Jarno <aurel...@aurel32.net>
> Cc: Andreas Färber <afaer...@suse.de>
> Reported-by: Aurelien Jarno <aurel...@aurel32.net>
> Signed-off-by: Anthony Liguori <aligu...@us.ibm.com>
> ---
> Aurelien, could you please try this patch with your PPC test case?
> ---
> qom/object.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/qom/object.c b/qom/object.c
> index 75e6aac..5ecfd28 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -132,7 +132,13 @@ TypeImpl *type_register(const TypeInfo *info)
>
> TypeImpl *type_register_static(const TypeInfo *info)
> {
> - return type_register(info);
> + TypeImpl *impl;
> +
> + impl = type_register(info);
> + impl->name = info->name;
> + impl->parent = info->parent;
> +
> + return impl;
> }
>
> static TypeImpl *type_get_by_name(const char *name)
> @@ -449,10 +455,16 @@ Object *object_dynamic_cast_assert(Object *obj, const
> char *typename)
> ObjectClass *object_class_dynamic_cast(ObjectClass *class,
> const char *typename)
> {
> - TypeImpl *target_type = type_get_by_name(typename);
> + TypeImpl *target_type;
> TypeImpl *type = class->type;
> ObjectClass *ret = NULL;
>
> + if (type->name == typename || type->parent == typename) {
> + return class;
> + }
> +
> + target_type = type_get_by_name(typename);
> +
> if (!target_type) {
> /* target class type unknown, so fail the cast */
> return NULL;
Unfortunately it doesn't fix the problem. I only see a 0.5% improvement,
which might be in the noise. I still see g_hash_table_lookup and
g_str_hash quite high in perf top.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurel...@aurel32.net http://www.aurel32.net
