java - 如何使用 JMH 测量平均冷启动时间？

Question

在 JMH(Java Microbenchmark Harness)中，我们可以使用

@BenchmarkMode(Mode.AverageTime)
@Warmup(iterations = 10)
@Measurement(iterations = 10)

评估 JVM 预热后执行的平均时间。
我们也可以使用

@BenchmarkMode(Mode.SingleShotTime)
@Measurement(iterations = 1)

估计执行的冷启动时间。但这只会执行一次基准测试，这可能会引入偏差。那么有没有什么方法可以评估JMH中冷启动的平均时间呢？

Answer 1

根据 Alexey himself (虽然从 2014 年开始):

Single-shot benchmarks were originally destined to run a single measurement iteration over multiple forks -- the scenarios to estimate "cold" performance. But for many cases, you might want more measurement iterations there especially if you are running only a single fork, because more samples would be generated.

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class AverageSingleShot {

    public static void main(String[] args) throws Exception {
        Options opt = new OptionsBuilder()
            .include(AverageSingleShot.class.getSimpleName())
            .build();

        new Runner(opt).run();
    }

    @Fork(100)
    @Benchmark
    @BenchmarkMode(Mode.SingleShotTime)
    public int test() {
        return ThreadLocalRandom.current().nextInt() + ThreadLocalRandom.current().nextInt();
    }

}

除了这会告诉你平均值的事实(参见 100 ):

 Benchmark               Mode  Cnt      Score      Error  Units
 AverageSingleShot.test    ss  100  41173.540 ± 2871.546  ns/op
 

您还将获得 Percentiles和一个 Histogram .