[master] RFR: Trim identity-hashcode to 25bit [v2]
rkennke at openjdk.java.net
Mon May 10 19:00:55 UTC 2021
> I'd like to trim the identity hashcode to 25 bits to make room in the upper 32bits for the compressed class-pointer.
> This could in theory regress performance on workloads that make heavy use of i-hashes, but I could not show this in practice (by specjvm workloads like compiler which uses lots of ihashes).
> Next step would be to move the Klass* into the upper 32bit part. (If you look closely, this would be the exact header layout of 32bit JVMs.) And then get rid of the dedicated Klass* field. :-D Eventually I'd make ihash-bits and klass* bits configurable to trade one for the other.
> - [x] some manual benchmarks
> - [x] tier1
> - [ ] tier2
Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:
- Fix docs about new header layout
- Adjust testcase to reflect new header layout
- all: https://git.openjdk.java.net/lilliput/pull/3/files
- new: https://git.openjdk.java.net/lilliput/pull/3/files/c3790d0c..c658bb8c
- full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=3&range=01
- incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=3&range=00-01
Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
Fetch: git fetch https://git.openjdk.java.net/lilliput pull/3/head:pull/3
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