RFR(M): 8231460: Performance issue (CodeHeap) with large free blocks

Schmidt, Lutz lutz.schmidt at sap.com
Thu Oct 17 07:28:17 UTC 2019

Dear all, 

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. 

Bug:    https://bugs.openjdk.java.net/browse/JDK-8231460 
Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8231460.00/ 

Please have a look.
Thank you,

More information about the hotspot-compiler-dev mailing list