Il 11/05/2013 00:58, Anthony Liguori ha scritto:
> Aurelien Jarno <aurel...@aurel32.net> writes:
>
>> 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;
>>> }
This is ok with a comment.
>>> 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;
>>> + }
I prefer my patch 3/9. With the hunk above, it works fine for the
simple case of casts in a device model's callbacks (testing type->parent
would almost always fail, so it is not worthwhile).
Unfortunately, strcmp is just as bad as a hashtable lookup (both are
O(n) in the size the string, instead of O(1)).
Paolo
>>> + 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.
>
> I was afraid of this. I assume the cast comes somewhere other than
> where the type was registered.
>
> This patch should address that. Could you post an image too? Then I
> don't have to keep bugging you with updated patches.
>
>
>
>
> Regards,
>
> Anthony Liguori
>
>>
>> --
>> Aurelien Jarno GPG: 1024D/F1BCDB73
>> aurel...@aurel32.net http://www.aurel32.net
