Java 降低新JVM的性能_Java_Performance_Jvm_Jmh

Java 降低新JVM的性能

java performance jvm

Java 降低新JVM的性能,java,performance,jvm,jmh,Java,Performance,Jvm,Jmh,在较新的JVM上，对for循环中数组中的所有元素求和的性能（吞吐量）比在Java1.8.0JDK的JVM上慢。我执行了JHM基准测试（下图）。在每次测试之前，源代码由提供的javac.exe编译并由java.exe运行，这两个二进制文件都由选定的JDK提供。测试是在Windows 10上执行的，由powershell脚本启动，没有任何程序在后台运行（没有其他JVM）。这台计算机配备了32GB的RAM，因此没有使用硬盘上的虚拟内存阵列中的10M元素：阵列中的100M元素：我的测试的源代码

在较新的JVM上，对for循环中数组中的所有元素求和的性能（吞吐量）比在Java1.8.0JDK的JVM上慢。我执行了JHM基准测试（下图）。在每次测试之前，源代码由提供的javac.exe编译并由java.exe运行，这两个二进制文件都由选定的JDK提供。测试是在Windows 10上执行的，由powershell脚本启动，没有任何程序在后台运行（没有其他JVM）。这台计算机配备了32GB的RAM，因此没有使用硬盘上的虚拟内存

阵列中的10M元素：

阵列中的100M元素：

我的测试的源代码：

@Param({"10000000", "100000000"})
public static int ELEMENTS;

public static void main(String[] args) throws RunnerException, IOException {
    File outputFile = new File(args[0]);

    int javaMajorVersion = Integer.parseInt(System.getProperty("java.version").split("\\.")[0]);

    ChainedOptionsBuilder builder = new OptionsBuilder()
            .include(IteratingBenchmark.class.getSimpleName())
            .mode(Mode.Throughput)
            .forks(2)
            .measurementTime(TimeValue.seconds(10))
            .measurementIterations(50)
            .warmupTime(TimeValue.seconds(2))
            .warmupIterations(10)
            .resultFormat(ResultFormatType.SCSV)
            .result(outputFile.getAbsolutePath());

    if (javaMajorVersion > 8) {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g", "--enable-preview");
    } else {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g");
    }

    new Runner(builder.build()).run();
}

@Benchmark
public static void cStyleForLoop(Blackhole bh, MockData data) {
    long sum = 0;
    for (int i = 0; i < data.randomInts.length; i++) {
        sum += data.randomInts[i];
    }

    bh.consume(sum);
}

@State(Scope.Thread)
public static class MockData {
    private int[] randomInts = new int[ELEMENTS];

    @Setup(Level.Iteration)
    public void setup() {
        Random r = new Random();
        this.randomInts = Stream.iterate(r.nextInt(), i -> i + r.nextInt(1022) + 1).mapToInt(Integer::intValue).limit(ELEMENTS).toArray();
    }
}

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;331,446104;5,563589;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;33,757268;0,431403;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,728461;4,823611;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,075948;0,062830;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,914782;4,450969;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,095232;0,075051;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;325,103055;4,933257;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,228403;0,067954;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,861148;0,443404;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,863602;0,035781;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,781930;0,481579;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,873509;0,033055;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;343,530895;0,445551;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;34,287083;0,035028;"ops/s";100000000

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;33,760346;0,089646;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,075120;0,086171;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,173939;0,044176;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,219283;0,062329;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,808609;0,072664;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,845817;0,074315;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;34,310620;0,087412;"ops/s";100000000

有没有任何有效的解释，为什么Java的新版本比1.8慢（OpenJDK 15除外）？

更新1:

@Param({"10000000", "100000000"})
public static int ELEMENTS;

public static void main(String[] args) throws RunnerException, IOException {
    File outputFile = new File(args[0]);

    int javaMajorVersion = Integer.parseInt(System.getProperty("java.version").split("\\.")[0]);

    ChainedOptionsBuilder builder = new OptionsBuilder()
            .include(IteratingBenchmark.class.getSimpleName())
            .mode(Mode.Throughput)
            .forks(2)
            .measurementTime(TimeValue.seconds(10))
            .measurementIterations(50)
            .warmupTime(TimeValue.seconds(2))
            .warmupIterations(10)
            .resultFormat(ResultFormatType.SCSV)
            .result(outputFile.getAbsolutePath());

    if (javaMajorVersion > 8) {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g", "--enable-preview");
    } else {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g");
    }

    new Runner(builder.build()).run();
}

@Benchmark
public static void cStyleForLoop(Blackhole bh, MockData data) {
    long sum = 0;
    for (int i = 0; i < data.randomInts.length; i++) {
        sum += data.randomInts[i];
    }

    bh.consume(sum);
}

@State(Scope.Thread)
public static class MockData {
    private int[] randomInts = new int[ELEMENTS];

    @Setup(Level.Iteration)
    public void setup() {
        Random r = new Random();
        this.randomInts = Stream.iterate(r.nextInt(), i -> i + r.nextInt(1022) + 1).mapToInt(Integer::intValue).limit(ELEMENTS).toArray();
    }
}

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;331,446104;5,563589;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;33,757268;0,431403;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,728461;4,823611;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,075948;0,062830;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,914782;4,450969;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,095232;0,075051;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;325,103055;4,933257;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,228403;0,067954;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,861148;0,443404;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,863602;0,035781;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,781930;0,481579;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,873509;0,033055;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;343,530895;0,445551;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;34,287083;0,035028;"ops/s";100000000

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;33,760346;0,089646;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,075120;0,086171;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,173939;0,044176;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,219283;0,062329;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,808609;0,072664;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,845817;0,074315;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;34,310620;0,087412;"ops/s";100000000

我对不同的Xmx/Xms值运行相同的测试（对于每个测试Xmx==Xms），结果如下：

更新2:

@Param({"10000000", "100000000"})
public static int ELEMENTS;

public static void main(String[] args) throws RunnerException, IOException {
    File outputFile = new File(args[0]);

    int javaMajorVersion = Integer.parseInt(System.getProperty("java.version").split("\\.")[0]);

    ChainedOptionsBuilder builder = new OptionsBuilder()
            .include(IteratingBenchmark.class.getSimpleName())
            .mode(Mode.Throughput)
            .forks(2)
            .measurementTime(TimeValue.seconds(10))
            .measurementIterations(50)
            .warmupTime(TimeValue.seconds(2))
            .warmupIterations(10)
            .resultFormat(ResultFormatType.SCSV)
            .result(outputFile.getAbsolutePath());

    if (javaMajorVersion > 8) {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g", "--enable-preview");
    } else {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g");
    }

    new Runner(builder.build()).run();
}

@Benchmark
public static void cStyleForLoop(Blackhole bh, MockData data) {
    long sum = 0;
    for (int i = 0; i < data.randomInts.length; i++) {
        sum += data.randomInts[i];
    }

    bh.consume(sum);
}

@State(Scope.Thread)
public static class MockData {
    private int[] randomInts = new int[ELEMENTS];

    @Setup(Level.Iteration)
    public void setup() {
        Random r = new Random();
        this.randomInts = Stream.iterate(r.nextInt(), i -> i + r.nextInt(1022) + 1).mapToInt(Integer::intValue).limit(ELEMENTS).toArray();
    }
}

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;331,446104;5,563589;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;33,757268;0,431403;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,728461;4,823611;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,075948;0,062830;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,914782;4,450969;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,095232;0,075051;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;325,103055;4,933257;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,228403;0,067954;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,861148;0,443404;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,863602;0,035781;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,781930;0,481579;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,873509;0,033055;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;343,530895;0,445551;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;34,287083;0,035028;"ops/s";100000000

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;33,760346;0,089646;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,075120;0,086171;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,173939;0,044176;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,219283;0,062329;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,808609;0,072664;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,845817;0,074315;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;34,310620;0,087412;"ops/s";100000000

首先，我将
```
Level.Iteration
```
更改为
```
Level.Trial
```
其次，我强制G1垃圾收集器
第三，Xmx/Xms被设置为8GB

结果：

原始数据：

@Param({"10000000", "100000000"})
public static int ELEMENTS;

public static void main(String[] args) throws RunnerException, IOException {
    File outputFile = new File(args[0]);

    int javaMajorVersion = Integer.parseInt(System.getProperty("java.version").split("\\.")[0]);

    ChainedOptionsBuilder builder = new OptionsBuilder()
            .include(IteratingBenchmark.class.getSimpleName())
            .mode(Mode.Throughput)
            .forks(2)
            .measurementTime(TimeValue.seconds(10))
            .measurementIterations(50)
            .warmupTime(TimeValue.seconds(2))
            .warmupIterations(10)
            .resultFormat(ResultFormatType.SCSV)
            .result(outputFile.getAbsolutePath());

    if (javaMajorVersion > 8) {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g", "--enable-preview");
    } else {
        builder = builder.jvmArgs("-Xms20g", "-Xmx20g");
    }

    new Runner(builder.build()).run();
}

@Benchmark
public static void cStyleForLoop(Blackhole bh, MockData data) {
    long sum = 0;
    for (int i = 0; i < data.randomInts.length; i++) {
        sum += data.randomInts[i];
    }

    bh.consume(sum);
}

@State(Scope.Thread)
public static class MockData {
    private int[] randomInts = new int[ELEMENTS];

    @Setup(Level.Iteration)
    public void setup() {
        Random r = new Random();
        this.randomInts = Stream.iterate(r.nextInt(), i -> i + r.nextInt(1022) + 1).mapToInt(Integer::intValue).limit(ELEMENTS).toArray();
    }
}

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;331,446104;5,563589;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;33,757268;0,431403;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,728461;4,823611;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,075948;0,062830;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;322,914782;4,450969;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,095232;0,075051;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;325,103055;4,933257;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;31,228403;0,067954;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,861148;0,443404;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,863602;0,035781;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;300,781930;0,481579;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;29,873509;0,033055;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;343,530895;0,445551;"ops/s";10000000
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;100;34,287083;0,035028;"ops/s";100000000

JDK 1.8.0_241:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;33,760346;0,089646;"ops/s";100000000

JDK 11.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,075120;0,086171;"ops/s";100000000

JDK 12.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,173939;0,044176;"ops/s";100000000

JDK 13.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;31,219283;0,062329;"ops/s";100000000

JDK 14.0.1:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,808609;0,072664;"ops/s";100000000

OpenJDK 14.0.2:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;29,845817;0,074315;"ops/s";100000000

OpenJDK 15:
"Benchmark";"Mode";"Threads";"Samples";"Score";"Score Error (99,9%)";"Unit";"Param: ELEMENTS"
"benchmark.IteratingBenchmark.cStyleForLoop";"thrpt";1;15;34,310620;0,087412;"ops/s";100000000

更新3:
我制作了一个包含基准源代码的脚本，该脚本使用我使用的JMH参数执行基准测试，自动生成png格式的绘图。此外，我在其他机器（Linux）上执行了基准测试。
Linux机器的结果似乎更乐观：

不幸的是，在我的Windows机器上，结果仍然显示性能下降（不包括JDK 15）

更新4:

-XX:-UseCountedLoopSafepoints的结果

：

即使从中复制基准测试并使用相同的参数运行，我仍然无法再现结果。在我的环境中，JDK 14的执行速度与JDK 8一样快（甚至快一点）。因此，在这个答案中，我将根据编译代码的反汇编分析两个版本之间的差异

首先，让我们从同一供应商处获取最新的OpenJDK版本。
这里我比较了Windows 64位的和

JMH得分如下：

Benchmark                         (ELEMENTS)   Mode  Cnt    Score   Error  Units
IteratingBenchmark.cStyleForLoop    10000000  thrpt   30  263,137 ± 0,484  ops/s  # JDK 8
IteratingBenchmark.cStyleForLoop    10000000  thrpt   30  264,406 ± 0,788  ops/s  # JDK 14

现在，让我们使用内置的

-prof xperfasm

探查器运行JMH，以查看基准测试最热门部分的反汇编。预计约99.5%的CPU时间花费在C2编译的

cStyleForLoop

方法中

JDK 8上最热的区域

....[Hottest Region 1].............................................................................. C2, level 4, codes.dbg.IteratingBenchmark::cStyleForLoop, version 574 (71 bytes) 0x0000028c5607fc5f: add r10d,0fffffff9h 0x0000028c5607fc63: lea rax,[r12+rcx*8] 0x0000028c5607fc67: mov ebx,80000000h 0x0000028c5607fc6c: cmp r9d,r10d 0x0000028c5607fc6f: cmovl r10d,ebx 0x0000028c5607fc73: mov r9d,1h 0x0000028c5607fc79: cmp r10d,1h ╭ 0x0000028c5607fc7d: jle 28c5607fccch │ 0x0000028c5607fc7f: nop ;*lload_2 │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25) 0,07% │↗ 0x0000028c5607fc80: movsxd rbx,dword ptr [rax+r9*4+10h] 0,06% ││ 0x0000028c5607fc85: add rbx,r8 8,93% ││ 0x0000028c5607fc88: movsxd rcx,r9d 0,41% ││ 0x0000028c5607fc8b: movsxd r8,dword ptr [rax+rcx*4+2ch] 25,02% ││ 0x0000028c5607fc90: movsxd rdi,dword ptr [rax+rcx*4+14h] 0,10% ││ 0x0000028c5607fc95: movsxd rsi,dword ptr [rax+rcx*4+18h] 8,56% ││ 0x0000028c5607fc9a: movsxd rbp,dword ptr [rax+rcx*4+28h] 0,58% ││ 0x0000028c5607fc9f: movsxd r13,dword ptr [rax+rcx*4+1ch] 0,41% ││ 0x0000028c5607fca4: movsxd r14,dword ptr [rax+rcx*4+20h] 0,20% ││ 0x0000028c5607fca9: movsxd rcx,dword ptr [rax+rcx*4+24h] 8,85% ││ 0x0000028c5607fcae: add rdi,rbx 0,38% ││ 0x0000028c5607fcb1: add rsi,rdi 0,15% ││ 0x0000028c5607fcb4: add r13,rsi 8,57% ││ 0x0000028c5607fcb7: add r14,r13 13,76% ││ 0x0000028c5607fcba: add rcx,r14 5,51% ││ 0x0000028c5607fcbd: add rbp,rcx 8,50% ││ 0x0000028c5607fcc0: add r8,rbp ;*ladd ││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25) 8,95% ││ 0x0000028c5607fcc3: add r9d,8h ;*iinc ││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24) 0,40% ││ 0x0000028c5607fcc7: cmp r9d,r10d │╰ 0x0000028c5607fcca: jl 28c5607fc80h ;*if_icmpge │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@12 (line 24) ↘ 0x0000028c5607fccc: cmp r9d,edx 0x0000028c5607fccf: jnl 28c5607fce4h 0x0000028c5607fcd1: nop ;*lload_2 ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25) 0x0000028c5607fcd4: movsxd r10,dword ptr [rax+r9*4+10h] 0x0000028c5607fcd9: add r8,r10 ;*ladd ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25) ....................................................................................................
JDK 14上最热的区域

....[Hottest Region 1].............................................................................. c2, level 4, codes.dbg.IteratingBenchmark::cStyleForLoop, version 622 (147 bytes) ; - codes.dbg.IteratingBenchmark::cStyleForLoop@23 (line 25) 0x000001e844438f72: mov r11d,r10d 0x000001e844438f75: add r11d,0fffffff9h 0x000001e844438f79: lea rax,[r12+r9*8] 0x000001e844438f7d: mov ebx,1h 0x000001e844438f82: cmp r11d,1h 0x000001e844438f86: jle 1e8444390c0h ;*goto {reexecute=0 rethrow=0 return_oop=0} ; - codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24) ╭ 0x000001e844438f8c: jmp 1e844438ffah │ 0x000001e844438f8e: nop 0,04% │↗ 0x000001e844438f90: mov rsi,r8 ;*lload_2 {reexecute=0 rethrow=0 return_oop=0} ││ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25) 0,04% ││ ↗ 0x000001e844438f93: movsxd rdx,dword ptr [rax+rbx*4+10h] 8,41% ││ │ 0x000001e844438f98: movsxd rbp,dword ptr [rax+rbx*4+14h] 1,23% ││ │ 0x000001e844438f9d: movsxd r13,dword ptr [rax+rbx*4+18h] 0,03% ││ │ 0x000001e844438fa2: movsxd r8,dword ptr [rax+rbx*4+2ch] 23,87% ││ │ 0x000001e844438fa7: movsxd r11,dword ptr [rax+rbx*4+28h] 8,22% ││ │ 0x000001e844438fac: movsxd r9,dword ptr [rax+rbx*4+24h] 1,25% ││ │ 0x000001e844438fb1: movsxd rcx,dword ptr [rax+rbx*4+20h] 0,14% ││ │ 0x000001e844438fb6: movsxd r14,dword ptr [rax+rbx*4+1ch] 0,28% ││ │ 0x000001e844438fbb: add rdx,rsi 7,82% ││ │ 0x000001e844438fbe: add rbp,rdx 1,14% ││ │ 0x000001e844438fc1: add r13,rbp 0,17% ││ │ 0x000001e844438fc4: add r14,r13 14,57% ││ │ 0x000001e844438fc7: add rcx,r14 11,05% ││ │ 0x000001e844438fca: add r9,rcx 5,26% ││ │ 0x000001e844438fcd: add r11,r9 6,32% ││ │ 0x000001e844438fd0: add r8,r11 ;*ladd {reexecute=0 rethrow=0 return_oop=0} ││ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25) 8,45% ││ │ 0x000001e844438fd3: add ebx,8h ;*iinc {reexecute=0 rethrow=0 return_oop=0} ││ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24) 1,15% ││ │ 0x000001e844438fd6: cmp ebx,edi │╰ │ 0x000001e844438fd8: jl 1e844438f90h ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0} │ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@12 (line 24) │ │ 0x000001e844438fda: mov r11,qword ptr [r15+110h] ; ImmutableOopMap {rax=Oop xmm0=Oop xmm1=Oop } │ │ ;*goto {reexecute=1 rethrow=0 return_oop=0} │ │ ; - (reexecute) codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24) 0,00% │ │ 0x000001e844438fe1: test dword ptr [r11],eax ;*goto {reexecute=0 rethrow=0 return_oop=0} │ │ ; - codes.dbg.IteratingBenchmark::cStyleForLoop@29 (line 24) │ │ ; {poll} 0,02% │ │ 0x000001e844438fe4: cmp ebx,dword ptr [rsp] │ ╭│ 0x000001e844438fe7: jnl 1e844439028h 0,00% │ ││ 0x000001e844438fe9: mov rsi,r8 │ ││ 0x000001e844438fec: vmovq r8,xmm0 │ ││ 0x000001e844438ff1: vmovq rdx,xmm1 0,01% │ ││ 0x000001e844438ff6: mov r11d,dword ptr [rsp] ↘ ││ 0x000001e844438ffa: mov ecx,r10d ││ 0x000001e844438ffd: sub ecx,ebx ││ 0x000001e844438fff: add ecx,0fffffff9h 0,00% ││ 0x000001e844439002: mov r9d,1f40h ││ 0x000001e844439008: cmp r9d,ecx ││ 0x000001e84443900b: mov edi,1f40h ││ 0x000001e844439010: cmovnle edi,ecx 0,02% ││ 0x000001e844439013: add edi,ebx ││ 0x000001e844439015: vmovq xmm0,r8 ││ 0x000001e84443901a: vmovq xmm1,rdx ││ 0x000001e84443901f: mov dword ptr [rsp],r11d 0,01% │╰ 0x000001e844439023: jmp 1e844438f93h ↘ 0x000001e844439028: vmovq rdx,xmm1 0x000001e84443902d: cmp ebx,r10d 0x000001e844439030: jnl 1e844439043h 0x000001e844439032: nop ;*lload_2 {reexecute=0 rethrow=0 return_oop=0} ; - codes.dbg.IteratingBenchmark::cStyleForLoop@15 (line 25) 0x000001e844439034: movsxd r11,dword ptr [rax+rbx*4+10h] 0x000001e844439039: add r8,r11 ;*ladd {reexecute=0 rethrow=0 return_oop=0} ; - codes.dbg.IteratingBenchmark::cStyleForLoop@24 (line 25) 0x000001e84443903c: inc ebx ;*iinc {reexecute=0 rethrow=0 return_oop=0} ; - codes.dbg.IteratingBenchmark::cStyleForLoop@26 (line 24) ....................................................................................................
如我们所见，循环体在两个JDK上的编译方式类似：

展开8个循环迭代
数组中有8个无边界检查加载，后面是8个
add
指令
加载顺序略有不同，但所有地址都共享相同或相邻的缓存线

关键区别在于，在JDK14上，循环迭代被分成两个嵌套块。这是JDK10中出现的优化结果。此优化的思想是将计数循环拆分为热内部部分（不使用safepoint轮询），以及外部部分（使用safepoint轮询指令）
C2 JIT将循环转换为

for (int i = 0; i < array.length; i += 8000) { for (int j = 0; j < 8000; j += 8) { int ix = i + j; int v0 = array[ix]; int v1 = array[ix + 1]; ... int v7 = array[ix + 7]; sum += v0 + v1 + ... + v7; } safepoint_poll(); }

for（int i=0；i
请注意，JDK 8版本在计数循环中根本没有safepoint轮询。一方面，这可以使循环运行得更快。但另一方面，这实际上对低延迟应用程序不利，因为暂停时间可能会随着整个循环的持续时间而增加 JDK 14在循环中插入一个safepoint轮询。这可能是您观察到的速度减慢的原因之一，但我不太相信这一点，因为由于循环条带挖掘优化，safepoint轮询在8000次迭代中只执行一次要验证这一点，您可以使用-XX:-UseCountedLoopSafepoints JVM选项禁用安全点轮询。在本例中，JDK14编译版本看起来与JDK8One几乎相同。基准分数也会如此。有没有原因使你的随机整数不是真正随机的，而是递增的（除非发生溢出）？没有。我想要一个重复值最少的数组。这种使用随机步长递增值的方法似乎很快就能填充数组。为什么重复数很重要？只需使用this.randomInts=r.ints（ELEMENTS.toArray（）。给他们所有相同的种子是否会产生影响，这将是有趣的。我不希望实际的int值对性能有任何影响。这在以前是很重要的，因为我在另一个测试中使用了它。当我注意到不同JVM版本之间的奇怪性能时，我尽可能地清除代码并发布在这里。我同意这很有趣。我稍后会检查。基准分数似乎受到了GC开销的影响，GC开销是由设置中不必要的分配造成的。1）使用Level.Trial 代替Level.Iteration 。2）在所有JDK版本上设置相同的GC（JDK 8和JDK 9中的默认GC不同+）非常好的描述，很好的@apangin。不幸的是，由于xperf错误（xperf.exe-error:0x00007FFFDFA8F88B处的指令引用了0xffffffffffffff处的内存。无法读取内存）。我认为性能下降只发生在我的机器上，因为它与其他机器相似或在增加。你的回答对我来说已经足够了。谢谢你抽出时间。