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.ch...@oracle.com> > Cc: core-libs-dev@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.ch...@oracle.com> wrote on 2019/08/21 01:21:42: > > > From: Mandy Chung <mandy.ch...@oracle.com> > > To: Kazunori Ogata <oga...@jp.ibm.com> > > Cc: core-libs-dev@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 > > > > > > >
