RFR: 8293020: jmod should not be treated as "small" tool for large modules [v3]

[Magnus Ihse Bursie]

On Mon, 29 Aug 2022 18:01:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> This is similar to [JDK-8245168](https://bugs.openjdk.org/browse/JDK-8245168), but the blanket change to allow all modules be compiled with default options is a net loss. Instead, we can hand-pick the major offenders (large modules) where running jmod with normal tool options improves performance.
>> 
>> I instrumented the jmod to tell me the times it needs to create individual modules, and hand-picked three top modules that take multiple seconds to run.
>> 
>> Motivational `make clean-images images` times:
>> 
>> 
>> # x86_64 Server, release
>> 
>> # Baseline
>> real	0m12.040s
>> user	1m4.872s
>> sys	0m10.805s
>> 
>> # Patched
>> real	0m10.785s  ; <--- 1.2s faster
>> user	1m7.031s
>> sys	0m10.985s
>> 
>> # x86_64 Server, fastdebug
>> 
>> # Baseline
>> real	0m19.263s
>> user	2m42.317s
>> sys	0m18.537s
>> 
>> # Patched
>> real	0m17.911s ;  <--- 1.1s faster
>> user	2m52.810s
>> sys	0m19.092s
>> 
>> 
>> # x86_64 Server, slowdebug
>> 
>> # Baseline
>> real	0m44.799s
>> user	10m7.106s
>> sys	0m17.578s
>> 
>> # Patched
>> real	0m46.975s   ; <--- 2.5 sec slower
>> user	11m1.155s
>> sys	0m17.060s
>> 
>> 
>> I think we can accept the `slowdebug` regression in favor of improvements on `release` and `fastdebug` that most people seem to be building every day.
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use :=

Marked as reviewed by ihse (Reviewer).

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PR: https://git.openjdk.org/jdk/pull/10062