Request for review 7177409: Perf regression in JVM_GetClassDeclaredFields after generic signature changes

[Jiangli Zhou]

Hi Coleen,

Thanks for the review!

Jiangli

On 06/20/2012 02:27 PM, Coleen Phillimore wrote:
>
> This looks good.
> Thanks,
> Coleen
>
> On 6/20/2012 5:10 PM, Jiangli Zhou wrote:
>> Hi David,
>>
>> Here is the updated weberv:
>>
>>   http://cr.openjdk.java.net/~jiangli/7177409/webrev.01/
>>
>> Thanks,
>> Jiangli
>>
>> On 06/19/2012 08:13 PM, Jiangli Zhou wrote:
>>> Hi David,
>>>
>>> Thanks for the review! Please see comments below.
>>>
>>> On 06/19/2012 06:41 PM, David Holmes wrote:
>>>> HI Jiangli,
>>>>
>>>> On 20/06/2012 3:32 AM, Jiangli Zhou wrote:
>>>>> Please review the following webrev that address the performance
>>>>> regression in JVM_GetClassDeclaredFields with very large class.
>>>>>
>>>>> http://cr.openjdk.java.net/~jiangli/7177409/webrev.00/
>>>>>
>>>>> In fieldDescriptor::generic_signature(), it now returns NULL 
>>>>> immediately
>>>>> if the access_flags indicates the field has no generic signature. 
>>>>> This
>>>>> avoids iterating though the fields unnecessarily. Mikael Gerdin has
>>>>> confirmed the change resolves the performance issue for
>>>>> JVM_GetClassDeclaredFields (thanks, Mikael!).
>>>>
>>>> Your change fixes the problem but I can't help but feel that there 
>>>> is an API problem here, and a usage problem in that this fragment 
>>>> in reflection.cpp:
>>>>
>>>>   if (java_lang_reflect_Field::has_signature_field() &&
>>>>       fd->generic_signature() != NULL) {
>>>>     Symbol*  gs = fd->generic_signature();
>>>>
>>>> should really be:
>>>>
>>>>   if (java_lang_reflect_Field::has_signature_field() &&
>>>>       fd->has_generic_signature()) {
>>>>     Symbol*  gs = fd->generic_signature();
>>>>
>>>> If the query is basically constant time the performance would not 
>>>> be impacted. In fact the current code seems to be relying on the C 
>>>> compiler to reuse the result of generic_signature() so that it 
>>>> doesn't actually call it twice. If it is calling it twice then an 
>>>> API change (for methods too) would yield an even better performance 
>>>> improvement.
>>>
>>> Yes, most compiler probably would not generate code to reload the 
>>> fd->generic_signature(). But adding an has_generic_signature() API 
>>> and use here seems good to me too. I can make that along with the 
>>> bug fix.
>>>
>>> Thanks,
>>>
>>> Jiangli
>>>
>>>>
>>>> Maybe an RFE ...
>>>>
>>>> David
>>>
>>