java-8 - Java 11 中的空方法明显比 Java 8 慢

Question

我正在使用 jmh 比较 JDK 8 和 11 的性能。 1.21 当我遇到一些令人惊讶的数字时:

Java version: 1.8.0_192, vendor: Oracle Corporation

Benchmark                Mode  Cnt  Score   Error  Units
MyBenchmark.emptyMethod  avgt   25  0.362 ± 0.001  ns/op


Java version: 9.0.4, vendor: Oracle Corporation

Benchmark                Mode  Cnt  Score    Error  Units
MyBenchmark.emptyMethod  avgt   25  0.362 ±  0.001  ns/op


Java version: 10.0.2, vendor: Oracle Corporation

Benchmark                Mode  Cnt  Score   Error  Units
MyBenchmark.emptyMethod  avgt   25  0.723 ± 0.001  ns/op


Java version: 11.0.1, vendor: Oracle Corporation

Benchmark                Mode  Cnt  Score   Error  Units
MyBenchmark.emptyMethod  avgt   25  0.724 ± 0.002  ns/op

OpenJDK 11 和 12 的性能类似于 OracleJDK 11。为简洁起见，我省略了它们的数字。

我知道微基准并不表示实际应用程序的性能行为。不过，我很好奇这种差异来自哪里。 有任何想法吗？

这是整个基准:

pom.xml :

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>jmh</groupId>
    <artifactId>empty-method</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>JMH benchmark sample: Java</name>

    <dependencies>
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-core</artifactId>
            <version>${jmh.version}</version>
        </dependency>
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-generator-annprocess</artifactId>
            <version>${jmh.version}</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <jmh.version>1.21</jmh.version>
        <javac.target>1.8</javac.target>
        <uberjar.name>benchmarks</uberjar.name>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-enforcer-plugin</artifactId>
                <version>1.4.1</version>
                <executions>
                    <execution>
                        <id>enforce-versions</id>
                        <goals>
                            <goal>enforce</goal>
                        </goals>
                        <configuration>
                            <rules>
                                <requireMavenVersion>
                                    <version>3.0</version>
                                </requireMavenVersion>
                            </rules>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <compilerVersion>${javac.target}</compilerVersion>
                    <source>${javac.target}</source>
                    <target>${javac.target}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <finalName>${uberjar.name}</finalName>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>org.openjdk.jmh.Main</mainClass>
                                </transformer>
                            </transformers>
                            <filters>
                                <filter>
                                    <!--
                                            Shading signed JARs will fail without this.
                                            http://stackoverflow.com/questions/999489/invalid-signature-file-when-attempting-to-run-a-jar
                                    -->
                                    <artifact>*:*</artifact>
                                    <excludes>
                                        <exclude>META-INF/*.SF</exclude>
                                        <exclude>META-INF/*.DSA</exclude>
                                        <exclude>META-INF/*.RSA</exclude>
                                    </excludes>
                                </filter>
                            </filters>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
        <pluginManagement>
            <plugins>
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>2.6.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-javadoc-plugin</artifactId>
                    <version>3.0.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.7.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-source-plugin</artifactId>
                    <version>3.0.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

src/main/java/jmh/MyBenchmark.java :

package jmh;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;

import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class MyBenchmark
{
    @Benchmark
    public void emptyMethod()
    {
    }
}

这是我使用的特定于 Windows 的脚本。将其翻译到其他平台应该很简单:

set JAVA_HOME=C:\Program Files\Java\jdk1.8.0_192
call mvn -V -Djavac.target=1.8 clean install
"%JAVA_HOME%\bin\java" -jar target\benchmarks.jar

set JAVA_HOME=C:\Program Files\Java\jdk-9.0.4
call mvn -V -Djavac.target=9 clean install
"%JAVA_HOME%\bin\java" -jar target\benchmarks.jar

set JAVA_HOME=C:\Program Files\Java\jdk-10.0.2
call mvn -V -Djavac.target=10 clean install
"%JAVA_HOME%\bin\java" -jar target\benchmarks.jar

set JAVA_HOME=C:\Program Files\Java\oracle-11.0.1
call mvn -V -Djavac.target=11 clean install
"%JAVA_HOME%\bin\java" -jar target\benchmarks.jar

我的运行环境是:

Apache Maven 3.6.0 (97c98ec64a1fdfee7767ce5ffb20918da4f719f3; 2018-10-24T14:41:47-04:00)
Maven home: C:\Program Files\apache-maven-3.6.0\bin\..
Default locale: en_CA, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"

更具体地说，我正在运行 Microsoft Windows [Version 10.0.17763.195] .

Answer 1

您正在测量空的基准，而不是空的方法。换句话说，测量处理基准测试本身的最小基础设施代码。这很容易剖析，因为您希望热路径上只有几条指令。 JMH的-prof perfasm或 -prof xperfasm会在几秒钟内给你那些 HitTest 门的指令。

我认为效果是由于Thread-Local Handshakes (JEP 312) ， 看:

8u191:0.389 ± 0.029 纳秒/运算
[到目前为止一切顺利]

  3.60%  ↗  ...a2: movzbl 0x94(%r8),%r10d
  0.63%  │  ...aa: add    $0x1,%rbp
 32.82%  │  ...ae: test   %eax,0x1765654c(%rip) ; global safepoint poll
 58.14%  │  ...b4: test   %r10d,%r10d
         ╰  ...b7: je     ...a2

11.0.2:0.585 ± 0.014 ns/操作 [哎呀，回归]

  0.31%  ↗  ...70: movzbl 0x94(%r9),%r10d    
  0.19%  │  ...78: mov    0x108(%r15),%r11  ; reading the thread-local poll addr
 25.62%  │  ...7f: add    $0x1,%rbp          
 35.10%  │  ...83: test   %eax,(%r11)       ; thread-local safepoint poll
 34.91%  │  ...86: test   %r10d,%r10d
         ╰  ...89: je     ...70

11.0.2，-XX:-ThreadLocalHandshakes:0.399 ± 0.048 ns/op [返回 8u 性能]

  5.64%  ↗  ...62: movzbl 0x94(%r8),%r10d    
  0.91%  │  ...6a: add    $0x1,%rbp          
 34.36%  │  ...6e: test   %eax,0x179be88c(%rip) ; global safepoint poll
 54.79%  │  ...74: test   %r10d,%r10d
         ╰  ...77: je     ...62

我认为这在很大程度上是可见的，主要是在像这样的紧密循环中。

UPD:希望有更多细节 here .