Java 11中的空方法明显慢于Java 8 [英] Empty methods noticeably slower in Java 11 than Java 8
问题描述
我使用 jmh 1.21比较了JDK 8和11的性能当我遇到一些令人惊讶的数字时：
I was comparing the performance of JDK 8 and 11 using jmh 1.21 when I ran across some surprising numbers:
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执行类似于OracleJDK 11.为简洁起见，我省略了它们的数字。
OpenJDK 11 and 12 perform similar to OracleJDK 11. I have omitted their numbers for the sake of brevity.
我知道微基准测试并不表示现实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？
I understand that microbenchmarks do not indicate the performance behavior of real-life applications. Still, I'm curious where this difference is coming from. Any ideas?
这是完整的基准：
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Windows特定脚本。将它翻译成其他平台应该是微不足道的：
Here is the Windows-specific script I use. It should be trivial to translate it to other platforms:
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
我的运行时环境是：
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] 。
More specifically, I am running Microsoft Windows [Version 10.0.17763.195].
推荐答案
您正在测量空基准，而不是空方法。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，因为您只希望在热门路径上有一些指令。 JMH的 -prof perfasm 或 -prof xperfasm 会在几秒钟内给你最热门的指示。
You are measuring empty benchmarks, not empty methods. In other words, measuring the minimal infrastructure code that handles the benchmark itself. This is easy to dissect, because you'd expect only a few instructions on the hot path. JMH's -prof perfasm or -prof xperfasm would give you those hottest instructions in seconds.
我认为效果是由于线程局部握手（JEP 312），见：
I think the effect is due to Thread-Local Handshakes (JEP 312), see:
8u191：0.389±0.029 ns / op
[到目前为止很好]
8u191: 0.389 ± 0.029 ns/op [so far so good]
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 / op [oops，regression]
11.0.2: 0.585 ± 0.014 ns/op [oops, regression]
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 perf]
11.0.2, -XX:-ThreadLocalHandshakes: 0.399 ± 0.048 ns/op [back to 8u perf]
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
我认为这主要是在像这样的紧密循环中很明显。
I think this is largely visible mostly in tight loops like this one.
UPD：希望更多细节此处。
UPD: Hopefully, more details here.
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