Saint's Log

Running the JMH Benchmark

To build and run the JMH benchmark, ensure Maven is installed (the mvn command should be available in the shell). On Ubuntu, this is as easy as running sudo apt install maven then setting up JMH using the steps below.

git clone https://github.com/swesonga/benchmarks
cd benchmarks
cd java/jmh
./setup_jmh_jdk_micros.sh
./run_jmh_jdk_micros.sh Parallel 1 2 10 5 5

The setup_jmh_jdk_micros.sh script builds the JMH JDK microbenchmarks and the run_jmh_jdk_micros.sh run the benchmark. Someone recently asked why there are 2 java processes shown in top when the run_jmh_jdk_micros.sh script runs given that it launches only 1 java process. I learned from this site how to use top to see java processes only: run top, type ‘o’, then type ‘COMMAND=java’ and press ENTER. This is the resulting output from the top command:

top - 22:15:21 up  8:15,  1 user,  load average: 1.73, 0.66, 0.30
Tasks: 330 total,   1 running, 329 sleeping,   0 stopped,   0 zombie
%Cpu(s): 20.9 us,  0.6 sy,  0.0 ni, 78.3 id,  0.0 wa,  0.0 hi,  0.2 si,  0.0 st
MiB Mem :  15415.5 total,   5837.9 free,   5436.0 used,   4141.6 buff/cache
MiB Swap:   2048.0 total,   2048.0 free,      0.0 used.   9568.6 avail Mem 

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                          
  22007 saint     20   0 5009436   1.1g  22464 S 345.3   7.2   1:02.74 java                                                                                             
  21927 saint     20   0 5607592   1.1g  23100 S   0.3   7.2   0:01.08 java

Sure enough, there are 2 java processes, each with 1.1g RES. This can also be confirmed by running the ps -aux | grep java command.

saint      21927  0.2  7.2 5607592 1141808 pts/2 Sl+  22:15   0:01 /home/saint/java/binaries/jdk/x64/jdk-21.0.1+12/bin/java -Xms1G -Xmx1G -XX:+AlwaysPreTouch -XX:+UseLargePages -jar jmh-jdk-microbenchmarks/micros-uber/target/micros-uberpackage-1.0-SNAPSHOT.jar -f 1 -si true -w 10 -i 5 -wi 5 -t 2 -o ./applogs/Parallel-1G-2024-02-02_22-15-03.txt -rff ./applogs/Parallel-1G-2024-02-02_22-15-03_machine.txt -rf text (?i)\.*(atomic|lock|volatile|ConcurrentHashMap|ProducerConsumer|Queues|ThreadLocalRandomNextInt)\.*
saint      22237  200  7.1 4876316 1125396 pts/2 Sl+  22:21   2:16 /home/saint/java/binaries/jdk/x64/jdk-21.0.1+12/bin/java -Xms1G -Xmx1G -XX:+AlwaysPreTouch -XX:+UseLargePages -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -DcompilerBlackholesEnabled=true -XX:CompileCommandFile=/tmp/jmh12734456823702200189compilecommand -cp jmh-jdk-microbenchmarks/micros-uber/target/micros-uberpackage-1.0-SNAPSHOT.jar org.openjdk.jmh.runner.ForkedMain 127.0.0.1 36835

Notice that one of the processes has an IP address and what is most likely a port number. Without knowing anything else, this would suggest a client/server model in use. To better understand why there are 2 java processes, let us see look at how the run script launches Java. It passes flags like -f 1 to the benchmark jar file. What parses these flags?

The benchmark JAR file is created from a pom.xml file containing a mainClass attribute of org.openjdk.jmh.Main. That’s the class responsible for parsing these flags. This Main class uses the CommandLineOptions class to parse arguments like -f 1 then executes the Runner.run() method. Runner.runBenchmarks() checks whether the benchmarks should be run embedded or forked. runBenchmarksEmbedded() has a warning about using non-forked runs only for debugging purposes. This answers the question of why there are 2 JVMs: we are running in forked mode. runSeparate() has a getForkedMainCommand() method, which suggests that there is most likely a way to pass custom arguments to the ForkedMain JVM.

Now that we understand why there are 2 JVMs, can we control the heap size of each of them independently? The CommandLineOptions class has a list of all the supported arguments. Notice the jvmArgs, jvmArgsAppend, and jvmArgsAppend arguments! These suggest that we can indeed control the heap sizes of each of the JVMs. Use the jvmArgsAppend flag in the run_jmh_jdk_micros.sh script (e.g. just before the benchmark_filter_regex to specify a custom heap size for the forked java process (independent of the jvm_heap_size_opts).

Installing Maven

I did not have Java set up on my Ubuntu VM. Therefore, setting up MVN installed Java and many other dependencies. I decided to list these here for future reference.

saint@vm1ubuntu:~/java$ sudo apt install maven
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  ca-certificates-java default-jre-headless java-common libaopalliance-java libapache-pom-java libatinject-jsr330-api-java libcdi-api-java libcommons-cli-java
  libcommons-io-java libcommons-lang3-java libcommons-parent-java libgeronimo-annotation-1.3-spec-java libgeronimo-interceptor-3.0-spec-java libguava-java
  libguice-java libhawtjni-runtime-java libjansi-java libjansi-native-java libjsr305-java libmaven-parent-java libmaven-resolver-java libmaven-shared-utils-java
  libmaven3-core-java libplexus-cipher-java libplexus-classworlds-java libplexus-component-annotations-java libplexus-interpolation-java libplexus-sec-dispatcher-java
  libplexus-utils2-java libsisu-inject-java libsisu-plexus-java libslf4j-java libwagon-file-java libwagon-http-shaded-java libwagon-provider-api-java
  openjdk-11-jre-headless
Suggested packages:
  default-jre libaopalliance-java-doc libatinject-jsr330-api-java-doc libel-api-java libcommons-io-java-doc libcommons-lang3-java-doc libasm-java libcglib-java
  libjsr305-java-doc libmaven-shared-utils-java-doc liblogback-java libplexus-classworlds-java-doc libplexus-sec-dispatcher-java-doc libplexus-utils2-java-doc junit4
  testng libcommons-logging-java liblog4j1.2-java fonts-dejavu-extra fonts-ipafont-gothic fonts-ipafont-mincho fonts-wqy-microhei | fonts-wqy-zenhei
The following NEW packages will be installed:
  ca-certificates-java default-jre-headless java-common libaopalliance-java libapache-pom-java libatinject-jsr330-api-java libcdi-api-java libcommons-cli-java
  libcommons-io-java libcommons-lang3-java libcommons-parent-java libgeronimo-annotation-1.3-spec-java libgeronimo-interceptor-3.0-spec-java libguava-java
  libguice-java libhawtjni-runtime-java libjansi-java libjansi-native-java libjsr305-java libmaven-parent-java libmaven-resolver-java libmaven-shared-utils-java
  libmaven3-core-java libplexus-cipher-java libplexus-classworlds-java libplexus-component-annotations-java libplexus-interpolation-java libplexus-sec-dispatcher-java
  libplexus-utils2-java libsisu-inject-java libsisu-plexus-java libslf4j-java libwagon-file-java libwagon-http-shaded-java libwagon-provider-api-java maven
  openjdk-11-jre-headless
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