On Thu, 24 Apr 2025 10:37:56 GMT, Radim Vansa <rva...@openjdk.org> wrote:
> This optimization is a followup to https://github.com/openjdk/jdk/pull/24290 > trying to reduce the performance regression in some scenarios introduced in > https://bugs.openjdk.org/browse/JDK-8292818 . Based both on performance and > memory consumption it is a (better) alternative to > https://github.com/openjdk/jdk/pull/24713 . > > This PR optimizes local field lookup in classes with more than 16 fields; > rather than sequentially iterating through all fields during lookup we sort > the fields based on the field name. The stream includes extra table after the > field information: for field at position 16, 32 ... we record the > (variable-length-encoded) offset of the field info in this stream. On field > lookup, rather than iterating through all fields, we iterate through this > table, resolve names for given fields and continue field-by-field iteration > only after the last record (hence at most 16 fields). > > In classes with <= 16 fields this PR reduces the memory consumption by 1 byte > that was left with value 0 at the end of stream. In classes with > 16 fields > we add extra 4 bytes with offset of the table, and the table contains one > varint for each 16 fields. The terminal byte is not used either. > > My measurements on the attached reproducer > > hyperfine -w 50 -r 100 '/path/to/jdk-17/bin/java -cp /tmp CCC' > Benchmark 1: /path/to/jdk-17/bin/java -cp /tmp CCC > Time (mean ± σ): 51.3 ms ± 2.8 ms [User: 44.7 ms, System: 13.7 ms] > Range (min … max): 45.1 ms … 53.9 ms 100 runs > > hyperfine -w 50 -r 100 '/path/to/jdk25-master/bin/java -cp /tmp CCC' > Benchmark 1: /path/to/jdk25-master/bin/java -cp /tmp CCC > Time (mean ± σ): 78.2 ms ± 1.0 ms [User: 74.6 ms, System: 17.3 ms] > Range (min … max): 73.8 ms … 79.7 ms 100 runs > > (the jdk25-master above already contains JDK-8353175) > > hyperfine -w 50 -r 100 '/path/to/jdk25-this-pr/bin/java -cp /tmp CCC' > Benchmark 1: /path/to/jdk25-this-pr/jdk/bin/java -cp /tmp CCC > Time (mean ± σ): 38.5 ms ± 0.5 ms [User: 34.4 ms, System: 17.3 ms] > Range (min … max): 37.7 ms … 42.1 ms 100 runs > > While https://github.com/openjdk/jdk/pull/24713 returned the performance to > previous levels, this PR improves it by 25% compared to JDK 17 (which does > not contain the regression)! This time, the undisclosed production-grade > reproducer shows even higher improvement: > > JDK 17: 1.6 s > JDK 21 (no patches): 22 s > JDK25-master: 12.3 s > JDK25-this-pr: 0.5 s This pull request has now been integrated. Changeset: e18277b4 Author: Radim Vansa <rva...@openjdk.org> Committer: Coleen Phillimore <cole...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/e18277b470a162b9668297e8e286c812c4b0b604 Stats: 924 lines in 18 files changed: 854 ins; 20 del; 50 mod 8352075: Perf regression accessing fields Reviewed-by: coleenp, iklam, jsjolen ------------- PR: https://git.openjdk.org/jdk/pull/24847
