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我正在尝试对错误共享对程序性能的影响进行基准测试。

在此示例中：https ://github.com/lexburner/JMH-samples/blob/master/src/main/java/org/openjdk/jmh/samples/JMHSample_22_FalseSharing.java ，缓存行填充导致性能提高数量级。

但是，当我使用 project panamas Foreign Memory Access API 时，缓存行填充实际上会使性能稍微变差。MemorySegments 是否隐式使用填充？还有什么可能导致这种行为？

我已经尝试在不同的硬件上运行基准测试并以相同的结果关闭超线程。

基准详细信息：

@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(5)
public class JMH_FalseSharing {

    @State(Scope.Group)
    public static class StateBaseline {
        @TearDown(Level.Trial)
        public void tearDown(){
            rs.close();
        }

        ResourceScope rs = ResourceScope.newSharedScope();
        static final VarHandle VH;
        final MemorySegment readSegment = MemorySegment.allocateNative(MemoryLayouts.JAVA_LONG, rs);
        final MemorySegment writeSegment = MemorySegment.allocateNative(MemoryLayouts.JAVA_LONG, rs);

        static{
            VH = MemoryLayouts.JAVA_LONG.varHandle(long.class);
        }
    }
    
    @State(Scope.Group)
    public static class StatePadded {
        @TearDown(Level.Trial)
        public void tearDown(){
            rs.close();
        }
    
        ResourceScope rs = ResourceScope.newSharedScope();
        static final VarHandle VH;
        private static final GroupLayout gl = MemoryLayout.structLayout(
            MemoryLayout.paddingLayout(448L),
            MemoryLayouts.JAVA_LONG.withName("val"),
            MemoryLayout.paddingLayout(448L)
            );
            
        final MemorySegment readSegment  = MemorySegment.allocateNative(gl, rs);
        final MemorySegment writeSegment = MemorySegment.allocateNative(gl, rs);

        static{
            VH = gl.varHandle(long.class, MemoryLayout.PathElement.groupElement("val"));
        }
    }
    
    @Group("baseline")
    @Benchmark
    public void baselineWrite(StateBaseline baselineState){
        StateBaseline.VH.setRelease(baselineState.writeSegment, (long)StateBaseline.VH.getAcquire(baselineState.writeSegment) + 1);
    }

    @Group("baseline")
    @Benchmark
    public void baselineRead(Blackhole blackhole, StateBaseline baselineState){
        blackhole.consume((long)StateBaseline.VH.getAcquire(baselineState.readSegment));
    }
    
    @Group("padded")
    @Benchmark
    public void paddedWrite(StatePadded paddedState){
        StatePadded.VH.setRelease(paddedState.writeSegment, (long)StatePadded.VH.getAcquire(paddedState.writeSegment) + 1);
    }

    @Group("padded")
    @Benchmark
    public void paddedRead(Blackhole blackhole, StatePadded paddedState){
        blackhole.consume((long)StatePadded.VH.getAcquire(paddedState.readSegment));
    }
}
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