Benchmark modes

You can find examples of how to use the JMH at the following link: http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/. One way is by using the JMHSample_02_BenchmarkModes class, which demonstrates the use of different modes. There are five modes:

• Mode.Throughput: This means that the benchmark method is being continuously invoked in a time-bound iteration and calculates how many times this method can be invoked.

• Mode.AverageTime: This measures similarly to Mode.Throughput, but calculates the average execution time.

• Mode.SampleTime: This measures similarly to Mode.Throughput, but samples the execution time for time-bound iterations.
• Mode.SingleShotTime: This measures the invocation time of a single method, which can be useful for cold startup testing. Using this mode, you specify that you don't want to call the benchmark method continuously.
• Mode.All: This does all of the above. Multiple modes let you specify modes that you want separated by commas—@BenchmarkMode({Mode.Throughput, Mode.AverageTime, Mode.SampleTime, Mode.SingleShotTime}).

We could rewrite our testMethod() as follows:

@Benchmark
@BenchmarkMode(Mode.AverageTime)
public void testMethod() {
    int a = 3;
    int b = 4;
    int c = a + b;
}

And by running it with five iterations and a single fork, the output will be as follows:

 # Run progress: 0.00% complete, ETA 00:00:10
 # Fork: 1 of 1
 # Warmup Iteration 1: ≈ 10?? s/op
 # Warmup Iteration 2: ≈ 10?? s/op
 # Warmup Iteration 3: ≈ 10?? s/op
 # Warmup Iteration 4: ≈ 10?? s/op
 # Warmup Iteration 5: ≈ 10?? s/op
 Iteration 1: ≈ 10?? s/op
 Iteration 2: ≈ 10?? s/op
 Iteration 3: ≈ 10?? s/op
 Iteration 4: ≈ 10?? s/op
 Iteration 5: ≈ 10?? s/op
 
 Result "org.sample.MyBenchmark.testMethod":
 ≈ 10?? s/op
 
 # Run complete. Total time: 00:00:10
 
 Benchmark              Mode Cnt Score Error Units
 MyBenchmark.testMethod avgt 5 ≈ 10?? s/op

This means that the average execution time for testMethod() is 10^-9 which is equal to 0.000000001 seconds. If you want to get the results in another time unit, you have to use the @OutputTimeUnit annotation.