RFR: JDK-8229871: Improve performance of Method.copy() and leafCopy()

Claes Redestad claes.redestad at oracle.com
Tue Oct 8 13:31:29 UTC 2019 

Hi,

webrev.02 looks good to me.

I think the performance results makes sense since avoiding a volatile
store (and the potentially expensive store barriers this involves)
should be the main benefit. Adding a branch to avoid storing null would
help partially, but not hot Methods.

Pre-existing issue, but it's somewhat weird that we have two assignments
outside the package-private constructor: adding root and methodAccessor
to the constructor would make more immediate sense to me, since we do
the same thing at the only two callsites:

         Method res = new Method(clazz, name, parameterTypes, returnType,
                 exceptionTypes, modifiers, slot, signature,
                 annotations, parameterAnnotations, annotationDefault);
         res.root = root;
         res.methodAccessor = methodAccessor;

->

         Method res = new Method(clazz, name, parameterTypes, returnType,
                 exceptionTypes, modifiers, slot, signature,
                 annotations, parameterAnnotations, annotationDefault,
                 root, methodAccessor);

This package-private constructor could also be made private. My guess is
there was some time when this was used from outside Method and changing
it was deemed unsavory..

Thanks!

/Claes

On 2019-10-08 12:23, Kazunori Ogata wrote:
> Hi all,
> 
> I posted two changes and got reply that performance evaluation is needed.
> I found that making Method.methodAccessor non-volatile (webrev.02) is
> better than avoid copying methodAccessor value when it is null
> (webrev.01), as shown below.
> 
> So I'd like to ask review of the former change.  I updated weberv using
> the latest code base (though there was no difference from webrev.02):
> 
> Webrev: http://cr.openjdk.java.net/~ogatak/8229871/webrev.03/
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8229871
> 
> 
> For this performance evaluation, I calculated 75 percentile of 9 runs of
> SPECjbb2015 and 60 percentile of 50 runs of DaCapo to omit outliers.  I
> bound a JVM to a NUMA node and set the number of GC threads to the same as
> the number of physical cores.  These tuning reduced run-to-run fluctuation
> on POWER (as usual...).
> 
> SPECjbb2015:
>    webrev.02:  critical jOPS +1.6%, max jOPS +0.2%
>    webrev.01:  critical jOPS +0.4%, max jOPS +0.2%
> 
> 
> For DaCapo, some benchmark still improved performance and some degraded,
> but the geometric mean of all benchmarks were small:
>    weberv.02: +0.3%
>    weberv.01: +0.2%
> 
> The difference of improvement/degradation between the two changes in each
> benchmark were less than 0.8%.
> 
> The range of improvement/degradation in each benchmark were:
>    webrev.02: between +2.4% and -1.0%
>    webrev.01: between +1.6% and -1.8%
> 
> 
> So I think webrev.02 (i.e., making methodAccessor non-volatile) is a good
> change, since it improved SPECjbb critical jOPS by 1.6%.
> 
> 
> Regards,
> Ogata
> 
> 
> Kazunori Ogata/Japan/IBM wrote on 2019/08/27 15:41:39:
> 
>> From: Kazunori Ogata/Japan/IBM
>> To: Mandy Chung <mandy.chung at oracle.com>
>> Cc: core-libs-dev at openjdk.java.net
>> Date: 2019/08/27 15:41
>> Subject: Re: RFR: JDK-8229871: Improve performance of Method.copy() and
> leafCopy()
>>
>> Hi Mandy,
>>
>> Let me post interim results of the performance evaluation, though I'm
>> still measuring benchmarks and analyzing them.
>>
>> For SPECjbb2015, skipping storing null (webrev.01) was faster than
> making
>> methodAccessor non-volatile (webrev.02).  The improvements of each of
> the
>> patches in maxJOPS/criticalJOPS were 2.6%/3.9% and 1.8%/2.9%,
>> respectively.  This is only an average of six runs.
>>
>> For DaCapo, the results were mixed.  In some benchmark, both of the
>> changes degraded performance.  In some others, webrev.01 was better, but
> 
>> weberv.02 was better in some others.
>>
>> I'll continue evaluation, but it is helpful if you could give me some
>> hints on why webrev.01 can be better than webrev.02 in SPECjbb2015.
>>
>> Regards,
>> Ogata
>>
>> Kazunori Ogata/Japan/IBM wrote on 2019/08/21 20:02:41:
>>
>>> From: Kazunori Ogata/Japan/IBM
>>> To: Mandy Chung <mandy.chung at oracle.com>
>>> Cc: core-libs-dev at openjdk.java.net
>>> Date: 2019/08/21 20:02
>>> Subject: Re: RFR: JDK-8229871: Improve performance of Method.copy()
> and leafCopy()
>>>
>>> Hi Mandy,
>>>
>>> Thank you for reviewing the webrev.  I updated it to add a space after
> 
>>> "if" and also put four spaces for indentation (it was three).
>>>
>>> http://cr.openjdk.java.net/~ogatak/8229871/webrev.01/
>>>
>>> Thank you so much for checking the history of fieldAccessor.  I was
>>> surprised that fieldAccessor was made non-volatile in JDK5, but
>>> methodAccessor was left as volatile for 15 years after that...
>>>
>>> I agree we need benchmark data.  My simple micro benchmark that
> repeats
>>> invoking Class.getMethods() improved performance by 70% when it made
> non-
>>> volatile (as shown in the following webrev).  I'll try to run larger
>>> benchmarks, such as SPECjbb2015, to see real impact.
>>>
>>> http://cr.openjdk.java.net/~ogatak/8229871/webrev.02/
>>>
>>> Regards,
>>> Ogata
>>>
>>> Mandy Chung <mandy.chung at oracle.com> wrote on 2019/08/21 01:21:42:
>>>
>>>> From: Mandy Chung <mandy.chung at oracle.com>
>>>> To: Kazunori Ogata <OGATAK at jp.ibm.com>
>>>> Cc: core-libs-dev at openjdk.java.net
>>>> Date: 2019/08/21 01:21
>>>> Subject: [EXTERNAL] Re: RFR: JDK-8229871: Imporve performance of
>>>> Method.copy() and leafCopy()
>>>>
>>>> Hi Ogata,
>>>>
>>>> The patch looks okay.  Nit: please add a space between if and (.
>>>>
>>>> About volatile methodAccessor field, I checked the history.  Both
>>>> fieldAccessor and methodAccessor were started as volatile and the
>>>> fieldAccessor declaration was updated due to JDK-5044412.   As you
>>>> observe, I think the methodAccessor field could be made
> non-volatile.
>>>> OTOH that might impact when it's inflated to spin bytecode for this
>>>> method invocation.  I don't know how importance to keep its volatile
> vs
>>>> non-volatile in practice without doing benchmarking/real application
> 
>>>> testing.
>>>>
>>>> Mandy
>>>>
>>>> On 8/19/19 2:51 AM, Kazunori Ogata wrote:
>>>>> Hi,
>>>>>
>>>>> May I have review for "JDK-8229871: Imporve performance of
> Method.copy()
>>>>> and leafCopy()"?
>>>>>
>>>>> Method.copy() and leafCopy() creates a copy of a Method object
> with
>>>>> sharing MethodAccessor object. Since the methodAccessor field is a
>>>>> volatile variable, copying this field needs memory fence to ensure
> the
>>>>> field is visible to all threads on the weak memory platforms such
> as POWER
>>>>> and ARM.
>>>>>
>>>>> When the methodAccessor of the root object is null (i.e., not
> initialized
>>>>> yet), we do not need to copy the null value because this field of
> the
>>>>> copied object has been initialized to null in the constructor. We
> can
>>>>> reduce overhead of the memory fence only when the root's
> methodAccessor is
>>>>> non-null. This change improved performance by 5.8% using a micro
> benchmark
>>>>> that repeatedly invokes Class.getMethods().
>>>>>
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8229871
>>>>>
>>>>> Webrev: http://cr.openjdk.java.net/~ogatak/8229871/webrev.00/
>>>>>
>>>>>
>>>>> By the way, why Method.methodAccessor is volatile, while
>>>>> Field.fieldAccessor and Field.overrideFieldAccessor are not
> volatile?  I
>>>>> know the use of volatile reduces probability of creating
> duplicated method
>>>>> accessor, but the chance still exists.  I couldn't find the
> difference
>>>>> between Method and Field classes to make Method.methodAccessor
> volatile.
>>>>> If we can make it non-volatile, it is more preferable than a quick
> hack
>>>>> above.
>>>>>
>>>>>
>>>>> Regards,
>>>>> Ogata
>>>>>
>>>>
>>>>
> 
>

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