On Mon, 20 Jan 2025 16:20:20 GMT, Matthias Ernst <d...@openjdk.org> wrote:
>> Certain signatures for foreign function calls (e.g. HVA return by value)
>> require allocation of an intermediate buffer to adapt the FFM's to the
>> native stub's calling convention. In the current implementation, this buffer
>> is malloced and freed on every FFM invocation, a non-negligible overhead.
>>
>> Sample stack trace:
>>
>> java.lang.Thread.State: RUNNABLE
>> at jdk.internal.misc.Unsafe.allocateMemory0(java.base@25-ea/Native
>> Method)
>> ...
>> at
>> jdk.internal.foreign.abi.SharedUtils.newBoundedArena(java.base@25-ea/SharedUtils.java:386)
>> at
>> jdk.internal.foreign.abi.DowncallStub/0x000001f001084c00.invoke(java.base@25-ea/Unknown
>> Source)
>> ...
>> at
>> java.lang.invoke.Invokers$Holder.invokeExact_MT(java.base@25-ea/Invokers$Holder)
>>
>>
>> To alleviate this, this PR remembers and reuses up to two small intermediate
>> buffers per carrier-thread in subsequent calls.
>>
>> Performance (MBA M3):
>>
>>
>> master@764d70b7df18e288582e616c62b0d7078f1ff3aa
>> Benchmark Mode Cnt Score Error Units
>> PointsAlloc.circle_by_ptr avgt 30 9.197 ? 0.037 ns/op
>> PointsAlloc.circle_by_value avgt 30 42.195 ? 0.088 ns/op <=
>> #######
>> PointsAlloc.jni_ByteBuffer_alloc avgt 30 226.127 ? 35.378 ns/op
>> PointsAlloc.jni_long_alloc avgt 30 25.297 ? 2.457 ns/op
>> PointsAlloc.panama_alloc avgt 30 27.053 ? 1.915 ns/op
>>
>> After:
>> Benchmark Mode Cnt Score Error Units
>> PointsAlloc.circle_by_ptr avgt 30 9.156 ? 0.021 ns/op
>> PointsAlloc.circle_by_value avgt 30 11.995 ? 0.051 ns/op <=
>> #######
>> PointsAlloc.jni_ByteBuffer_alloc avgt 30 211.161 ? 23.284 ns/op
>> PointsAlloc.jni_long_alloc avgt 30 24.885 ? 2.461 ns/op
>> PointsAlloc.panama_alloc avgt 30 26.905 ? 1.935 ns/op
>>
>>
>> `-prof gc` also shows that the new call path is fully scalar-replaced vs 160
>> byte/call before.
>
> Matthias Ernst has updated the pull request incrementally with three
> additional commits since the last revision:
>
> - shift api boundary
> - move bench
> - revert formatting
src/java.base/share/classes/jdk/internal/foreign/abi/SharedUtils.java line 393:
> 391: MemorySegment unscoped = CallBufferCache.acquireOrAllocate(size);
> 392: Arena scope = Arena.ofConfined();
> 393: MemorySegment source = unscoped.reinterpret(scope, null);
I suggest passing the `scope` to `acquireOrAllocate` as well, so we only need a
single call to `reinterpret` (it has an overload that takes both a size and
arena. (And I think you can then also remove the `@SuppressWarnings` from this
method)
src/java.base/share/classes/jdk/internal/foreign/abi/SharedUtils.java line 395:
> 393: MemorySegment source = unscoped.reinterpret(scope, null);
> 394: // Preferable we'd like to register this cleanup in the line
> above
> 395: // but it breaks scalar replacement.
I have a fix for this issue. Will create a PR.
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)
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.
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?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922701981
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922701268
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922699935
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922700908
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1922698930
