RFR (XS): 8216316: jdk/jfr/event/gc/detailed/TestPromotionEventWithG1.java fails due to reserved TLAB area too large

[Thomas Schatzl]

Hi all,

  can I have reviews for this fix to some test options to make the
TestPromotionEventWithG1 test more stable on the platforms we support?

In particular, depending on hardware, the minimum TLAB size given in
the test was too small to accomodate the prefetching code C2 emits when
allocating objects.

The fix is to minimize this buffer by twiddling with prefetching
amounts, and increasing the minimum tlab size a bit - so that the test
still fails with the patch for 8212766 not applied.

Thanks go to Goetz from SAP who figured out the values for the
prefetching so that most supported systems worked.

@Goeth: can you check this fix on your systems too?

CR:
https://bugs.openjdk.java.net/browse/JDK-8216316
Webrev:
http://cr.openjdk.java.net/~tschatzl/8216316/
Testing:
Test failing test on various machines in our CI system

Thanks,
  Thomas