RFR: JDK-8229871: Improve performance of Method.copy() and leafCopy()
Kazunori Ogata
OGATAK at jp.ibm.com
Fri Oct 11 10:17:26 UTC 2019
Hi Peter,
Thank you for the comment and suggestion of the fix.
I tried to pick up your change w.r.t. methodAccessor:
https://cr.openjdk.java.net/~ogatak/8229871/webrev.04/
Regarding micro benchmark, my original motivation of this change is to
improve performance of Class.getMethods(), which calls Method.copy() for
each declared method to create a copy of Method[].
I measured my simple microbench:
https://cr.openjdk.java.net/~ogatak/8229871/GetMethodsBench.java
Base code: Elapsed time = 4808 ms
webrev.01: Elapsed time = 4536 ms (+ 6%)
webrev.02: Elapsed time = 2331 ms (+106%)
webrev.04: Elapsed time = 3746 ms (+ 28%)
I'll measure larger benchmark and try to think if we can reduce the
overhead of memory barrier.
Regards,
Ogata
Peter Levart <peter.levart at gmail.com> wrote on 2019/10/09 16:44:13:
> From: Peter Levart <peter.levart at gmail.com>
> To: Kazunori Ogata <OGATAK at jp.ibm.com>, core-libs-dev at openjdk.java.net
> Date: 2019/10/09 16:44
> Subject: [EXTERNAL] Re: RFR: JDK-8229871: Improve performance of
> Method.copy() and leafCopy()
>
> Hi Ogata,
>
> May I just add that volatile field ensured that MethodAccessor object
was
> correctly published. DelegatingMethodAccessortImpl is not safe to be
> published via data race because it contains plain `delegate` field
> initialized in the constructor. In addition, the object that is first
> assigned to that field is NativeMethodAccessorImpl which has plain
> `parent` field. You can get NPE when invoking the Method.invoke from
> multuiple threads if Method.methodAccessor is not volatile.
>
> In addition, It would be nice to have two microbenchmarks exercising:
> a) Method copy performance
> b) Method invocation performance
>
> Regards, Peter
>
> P.S. When exploring the possibility of an alternative MethodAccessor
> implementation (using MethodHandle(s)):
>
>
http://cr.openjdk.java.net/~plevart/jdk-dev/6824466_MHReflectionAccessors/
> webrev.00.2/
>
> ...I found out that it was possible to re-arrange the play between
> DelegatingMethodAccessorImpl, NativeMethodAccessorImpl and generated
> MethodAccessor in such a way that the DelegatingMethodAccessortImpl
> becomes safe to be published via data race. This allowed for
> Method.methodAccessor field to become plain field. In addition this
field
> can be made @Stable which further optimizes access to MethodAccessor
> instance when Method instance can be constant-folded, which showed in
> special microbenchmarks.
>
> So perhaps you could try to use above implementation (just changes to
> DelegatingMethodAccessorImpl, NativeMethodAccessorImpl and part of
> Reflection factory but without MH* stuff) and measure it against current
> and your implementation (which as shown above has a data-race flaw).
> On 10/8/19 12:23 PM, 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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