Aurelien Jarno <aurelien@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 <pbonzini@redhat.com>
>> Cc: Aurelien Jarno <aurelien@aurel32.net>
>> Cc: Andreas Färber <afaerber@suse.de>
>> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
>> Signed-off-by: Anthony Liguori <aliguori@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.

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.