On Mon, 9 Jun 2025 11:33:00 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 > > Radim Vansa has updated the pull request incrementally with one additional > commit since the last revision: > > Print debugging info for InstanceKlass There are more instances of these style errors that I've noted, please fix the other instances as well. src/hotspot/share/oops/fieldInfo.cpp line 132: > 130: // We use both name and signature during the comparison; while JLS > require unique > 131: // names for fields, JVMS requires only unique name + signature > combination. > 132: typedef struct { Style: Use C++ struct def (no typedef), don't use trailing _t in the name and write it as FieldPos. The fields are public, so no underscore as name prefix for them. src/hotspot/share/oops/fieldInfo.cpp line 140: > 138: > 139: class FieldInfoSupplier: public PackedTableBuilder::Supplier { > 140: private: Unnecessary private src/hotspot/share/oops/fieldInfo.cpp line 143: > 141: const field_pos_t* _positions; > 142: size_t _elements; > 143: public: Insert newline between public: and _elements ------------- PR Review: https://git.openjdk.org/jdk/pull/24847#pullrequestreview-2910061487 PR Review Comment: https://git.openjdk.org/jdk/pull/24847#discussion_r2135716601 PR Review Comment: https://git.openjdk.org/jdk/pull/24847#discussion_r2135716801 PR Review Comment: https://git.openjdk.org/jdk/pull/24847#discussion_r2135717226
