RFR: 8284880: Re-examine sun.invoke.util.Wrapper hash tables

[Erik Joelsson]

On Thu, 14 Apr 2022 11:19:04 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> This patch examines and optimizes `Wrapper` lookups.
> 
> First wrote a few simple microbenchmarks to verify there are actual speedups from using perfect hash tables in `sun.invoke.util.Wrapper` compared to simpler lookup mechanisms (such as if-else or switch). Turns out there _is_ a speed-up for the case of `char` -> `Wrapper`, but not when mapping from `Class<?>` -> `Wrapper`, so let's drop those. The `forPrimitiveType` case didn't use the `FROM_CHAR` table for some reason, which is remedied.  
> 
> Micros show benefits across the board for warmed up case:
> 
> 
> Baseline, OOTB
> Benchmark                  Mode  Cnt   Score   Error  Units
> Wrappers.forBasicType      avgt    5  14.387 ? 0.127  ns/op
> Wrappers.forPrimitive      avgt    5  38.818 ? 0.592  ns/op
> Wrappers.forPrimitiveType  avgt    5  26.085 ? 2.291  ns/op
> Wrappers.forWrapper        avgt    5  44.459 ? 1.635  ns/op
> 
> Patch, OOTB
> Benchmark                  Mode  Cnt   Score   Error  Units
> Wrappers.forBasicType      avgt    5  14.357 ? 0.133  ns/op
> Wrappers.forPrimitive      avgt    5  23.930 ? 0.071  ns/op
> Wrappers.forPrimitiveType  avgt    5  14.343 ? 0.017  ns/op
> Wrappers.forWrapper        avgt    5  27.622 ? 0.022  ns/op
> 
> 
> For `-Xint` case (`Wrapper` use is prominent during warmup, e.g., when spinning up of MHs) there are decent or even great wins in all cases but `forPrimitiveType` - which was changed from a simple switch to use the hash lookup. Since the interpreter penalty is small in absolute terms and the win on JITed code is significant this seems like a reasonable trade-off:
> 
> 
> Baseline, -Xint
> Benchmark                  Mode  Cnt     Score     Error  Units
> Wrappers.forBasicType      avgt    5  1246.144 ? 149.933  ns/op
> Wrappers.forPrimitive      avgt    5  4955.297 ? 329.869  ns/op
> Wrappers.forPrimitiveType  avgt    5   716.840 ?  62.568  ns/op
> Wrappers.forWrapper        avgt    5  5774.700 ? 367.627  ns/op
> 
> Patch, -Xint
> Benchmark                  Mode  Cnt     Score     Error  Units
> Wrappers.forBasicType      avgt    5  1068.096 ? 101.728  ns/op
> Wrappers.forPrimitive      avgt    5  1146.670 ?  59.142  ns/op
> Wrappers.forPrimitiveType  avgt    5   998.037 ? 118.144  ns/op
> Wrappers.forWrapper        avgt    5  3581.226 ?  20.167  ns/op

Build change looks ok.

make/test/BuildMicrobenchmark.gmk line 97:

> 95:     SRC := $(MICROBENCHMARK_SRC), \
> 96:     BIN := $(MICROBENCHMARK_CLASSES), \
> 97:     JAVAC_FLAGS := --add-exports java.base/sun.security.util=ALL-UNNAMED --add-exports java.base/sun.invoke.util=ALL-UNNAMED, \

Suggestion:

    JAVAC_FLAGS := --add-exports java.base/sun.security.util=ALL-UNNAMED \
        --add-exports java.base/sun.invoke.util=ALL-UNNAMED, \

-------------

Marked as reviewed by erikj (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8242