RFR(M): 8231460: Performance issue (CodeHeap) with large free blocks
lutz.schmidt at sap.com
Thu Oct 17 07:28:17 UTC 2019
may I please request reviews for this fix, addressing actually two current performance issues in CodeHeap management. One issue (the stupid one) could be eliminated completely. The other one, in the context of maintaining the code heap segment map, was tamed considerably.
From old to new, the following absolute times and speedup factors were observed:
speedup absolute time [Milliseconds]
old version new version
ppc fastdebug 4,700 69,593.484 14.833 (30,000 calls)
ppc release 4,600 70,069.517 15.215 (30,000 calls)
s390 fastdebug 3,500 7,778.500 2.220 (40,000 calls)
s390 release 6,700 6,935.371 1.026 (40,000 calls)
These results are far from clean room measurements. On the other hand, the improvements are so extreme that it can't be just measurement errors. And is it important if the factor is 4k or 3k?
The performance gain is achieved by taking advantage of properties of the CodeHeap segment map, not by improved coding techniques. You can find more detail in the bug description and as inline documentation in the source code.
Please have a look.
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