RFR: 8287788: reuse intermediate segments allocated during FFM stub invocations [v3]

[Matthias Ernst]

On Mon, 20 Jan 2025 17:22:09 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Matthias Ernst has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - shift api boundary
>>  - move bench
>>  - revert formatting
>
> test/micro/org/openjdk/bench/java/lang/foreign/CallOverheadByValue.java line 54:
> 
>> 52: @State(org.openjdk.jmh.annotations.Scope.Thread)
>> 53: @OutputTimeUnit(TimeUnit.NANOSECONDS)
>> 54: @Fork(value = 1, jvmArgs = {"-Xlog:gc", "--enable-native-access=ALL-UNNAMED", "-Djava.library.path=micro/native"})
> 
> FWIW, unfortunately there is no builtin support to run profilers through `make`. I personally have a separate script that runs the benchmarks.jar:
> 
> 
> ./build/$CONF/images/jdk/bin/java -jar ./build/$CONF/images/test/micro/benchmarks.jar -prof gc AllocTest.alloc_confined
> 
> 
> (where `$CONF` is your build configuration)

Removed.

> test/micro/org/openjdk/bench/java/lang/foreign/CallOverheadByValue.java line 98:
> 
>> 96:                             (SegmentAllocator) (_, _) -> dest,
>> 97:                             phi);
>> 98:         }
> 
> Would it be viable to measure just a single invocation? That way we can remove other things like the `asSlice` call, which might introduce noise.

Done. Numbers are now:


Benchmark                    Mode  Cnt  Score   Error  Units
CallOverheadByValue.byPtr    avgt   10  3.291 ? 0.031  ns/op
CallOverheadByValue.byValue  avgt   10  5.464 ? 0.007  ns/op

> test/micro/org/openjdk/bench/java/lang/foreign/CallOverheadByValue.java line 99:
> 
>> 97:                             phi);
>> 98:         }
>> 99:         return points;
> 
> I don't think `points` needs to be returned here?

Removed. I wanted to be conservative and give the "blackhole" something to work with, but I guess it can't optimize away an FFM call.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922727695
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922728050
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922727507