RFR: 8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter [v2]

[Richard Reingruber]

On Wed, 22 Jan 2025 21:52:02 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> PPC64 implementation of https://github.com/openjdk/jdk/commit/ead0116f2624e0e34529e47e4f509142d588b994. I have implemented a couple of rotate instructions.
>> The first commit only implements `lookup_secondary_supers_table_var` and uses it in C2. The second commit makes the changes to use it in the interpreter, runtime and C1.
>> C1 part is refactored such that the same code as before this patch is generated when `UseSecondarySupersTable` is disabled. Some stubs are modified to provide one more temp register.
>> 
>> Performance difference can be observed when C2 is disabled (measured on Power10):
>> 
>> 
>> -XX:TieredStopAtLevel=1 -XX:-UseSecondarySupersTable:
>> SecondarySuperCacheHits.test  avgt   15  13.028 ± 0.005  ns/op
>> SecondarySuperCacheInterContention.test     avgt   15  417.746 ± 19.046  ns/op
>> SecondarySuperCacheInterContention.test:t1  avgt   15  417.852 ± 17.814  ns/op
>> SecondarySuperCacheInterContention.test:t2  avgt   15  417.641 ± 23.431  ns/op
>> SecondarySuperCacheIntraContention.test  avgt   15  340.995 ± 5.620  ns/op
>> 
>> 
>> 
>> -XX:TieredStopAtLevel=1 -XX:+UseSecondarySupersTable:
>> SecondarySuperCacheHits.test  avgt   15  14.539 ± 0.002  ns/op
>> SecondarySuperCacheInterContention.test     avgt   15  25.667 ± 0.576  ns/op
>> SecondarySuperCacheInterContention.test:t1  avgt   15  25.709 ± 0.655  ns/op
>> SecondarySuperCacheInterContention.test:t2  avgt   15  25.626 ± 0.820  ns/op
>> SecondarySuperCacheIntraContention.test  avgt   15  22.466 ± 1.554  ns/op
>> 
>> 
>> `SecondarySuperCacheHits` seems to be slightly slower, but `SecondarySuperCacheInterContention` and `SecondarySuperCacheIntraContention` are much faster (when C2 is disabled).
>
> Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove early return from check_klass_subtype_slow_path.

src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2158:

> 2156:   std(super_klass, target_offset, sub_klass); // save result to cache
> 2157:   if (result_reg != noreg) { li(result_reg, 0); } // load zero result (indicates a hit)
> 2158:   if (L_success != nullptr) { b(*L_success); }

Handling `L_success != nullptr` should be put on the else-branch of the previous if-statement.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22881#discussion_r1927009873