"long" Assignment Only: 24 Nanoseconds per Step

JVM Tutorials - Herong's Tutorial Examples - Version 4.23, by Dr. Herong Yang

JVM Tutorials - Herong's Tutorial Examples

∟Micro Benchmark Tests on "long" Operations

∟"long" Assignment Only: 24 Nanoseconds per Step

This section provides a tutorial example on how to perform benchmark tests to find out how long each step will take to run assignment loop - 14 nanoseconds per step.

Using the empty loop execution time obtained from the previous tutorial as a baseline, I can do more interesting tests now.

This time I want to find out how long it will take to do an assignment operation in interpreted-only mode. Here is my test method for this:

/**
 * BenchmarkTestLong.java
 * Copyright (c) 2010, HerongYang.com, All Rights Reserved.
 */
class BenchmarkTestLong {
...
   // Test method for an assignment operation in a loop
   public static long assignment(int steps, BenchmarkRunner runner) {
      long x = 0;
      long i = 0;
      long last = steps;
      runner.startTimer();
      for (i=0; i<last; i++) {
         x = i;
      }
      runner.stopTimer();
      return x;
   }
}

Here are test results:

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 10
...
Runs: 100, Ave: 257, Min: 224, Max: 279 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 100
...
Runs: 100, Ave: 51, Min: 47, Max: 53 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 1000
...
Runs: 100, Ave: 27, Min: 27, Max: 28 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 10000
...
Runs: 100, Ave: 24, Min: 24, Max: 27 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 100000
...
Runs: 100, Ave: 24, Min: 24, Max: 25 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner 
BenchmarkTestLong assignment 10000 100 1000000
...
Runs: 100, Ave: 24, Min: 24, Max: 25 - Per step in nanoseconds

Conclusions based on the test result:

The result is very interesting. Adding an assignment operation in an loop made the loop to run faster! The assignment, the loop index incrementing and the loop termination checking take 24 nanoseconds per step.
I have no idea why this assignment loop runs 1 nanoseconds faster than an empty loop per step.

Last update: 2010.

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Downloading and Installing JDK 1.8.0 on Windows

Downloading and Installing JDK 1.7.0 on Windows

java.lang.Runtime Class - The JVM Instance

java.lang.System Class - The Operating System

ClassLoader Class - Class Loaders

Class Class - Class Reflections

Sun's JVM - Java HotSpot VM

JRockit JVM 28.2.7 by Oracle Corporation

JVM Runtime Data Areas