RFR (M): 8146987: Improve Parallel GC Full GC by caching results of live_words_in_range() [Was: Re: [PATCH] enhancement to ParallelScavenge Full GC]

ray alex sky1young at gmail.com
Thu Jan 14 14:54:16 UTC 2016

We previously evaluated some applications from JOlden, Dacapo and
SpecJVM2008 benchmark suites.
We believe these tests could reflect the essential behaviors of parallel
GC's full gc.

Specifically, the applications are:
BiSort, Em3d, MST, TreeAdd, Health, Perimeter (JOlden)
H2 (Dacapo)
Xml.validation, Compiler.compiler (SPECjvm2008)
with a 1GB heap size for all of them (except Health with 3GB).
The results are averagely 50% for them above.

Actually, the heap size is a factor that impacts the frequency of full gcs,
but does not influence the effect of this approach.
As long as a full gc is triggered, we believe this caching could bring
improvement, and the percentage could vary according to the access patterns
of objects in different programs.
Though in some scenarios the improvement may be less, it almost does not
impose any overhead.

Hoping these could be helpful for the testing.

I'm looking forward to your new test result of the patch and the upstream
Please remind me if I could help on the test.


2016-01-13 23:51 GMT+08:00 Thomas Schatzl <thomas.schatzl at oracle.com>:

> Hi Tianyang,
> On Sun, 2016-01-10 at 22:16 +0800, ray alex wrote:
> > Hi,
> > By following the conventions, I remove the prefix "get_" and rename
> > getter/setter to "last_query_*" in this patch version 4 (attached).
> > Besides, I ran the measurements mentioned before (both for version 3
> > and recheck this version 4 ), and there was no regressions.
> >
> > May I have your reviews on this patch?
> >
> > Thanks!
>  first, sorry for the delay, holidays and such...
> I created a CR for this enhancement at
> https://bugs.openjdk.java.net/browse/JDK-8146987
> I also made some webrevs for this change that fix some minor issues:
> base patch that includes some compilation fixes:
> http://cr.openjdk.java.net/~tschatzl/8146987/webrev.0/
> - recent changes introduced some merge errors in psParallelCompact,
> mostly due to Unified logging
> - the assert in psParallelCompact.cpp:3137 missed a parameter so the
> sources did not compile in any debug mode.
> Some minor style fixes:
> http://cr.openjdk.java.net/~tschatzl/8146987/webrev.1/ (full)
> http://cr.openjdk.java.net/~tschatzl/8146987/webrev.0_to_1/ (diff)
> - made a few of the new methods private
> - some coding style fixes: indentation, trailing white spaces, copyright
> dates
> - removed the new parMarkBitMap.inline.hpp again because its methods were
> only called from parMarkBitmap.cpp, fixed includes to parMarkBitmap.cpp.
> - prepare some push message, please check
> I did run internal gc testing on the .0 webrev (vm.gc testlist), and did
> some performance verification (mainly on specjbb201x as this was what was
> on hand). It does (as expected) improve the perf of full gc, although the
> improvements are not as high as mentioned in your initial email, around 15%
> average full gc time (for some rather specific configuration). That is
> still quite good imo.
> Reproducing the results has been one reason why this reply took a while,
> it needs a bit of carefully setting up tests to get results that are not
> drowned in noise due to gc occurring on widely different heap contents, and
> particularly ergonomics.
> Not sure how you managed to do this with something like dacapo.
> SPECjvm2008 in "realistic" configurations does not do a lot of (if any)
> full gcs.
> The change looks good to me now, but I need to do some more testing again
> with the .1 version, to make sure the cleanup did not introduce any
> regressions anywhere.
> Thanks,
>   Thomas

Lei Tianyang
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