What exactly is number of operations in JMH?

Question

The JavaDoc of annotation @OperationsPerInvocation in the Java Microbenchmarking Harness (JMH) states:

value public abstract int value

Returns: Number of operations per single Benchmark call. Default: 1

Being new to JMH I am wondering what type of operation (byte code operation, assembly code operation, Java operation etc) is meant here.

This question naturally refers to all places in JMH (documentation, output, comments etc) where the term 'operation' is used (e.g. "operation/time" unit or "time unit/operation").

Answer 1

In JMH, "operation" is an abstract unit of work. See e.g. the sample result:

Benchmark               Mode  Cnt  Score   Error  Units
MyBenchmark.testMethod  avgt    5  5.068 ± 0.586  ns/op

Here, the performance is 5.068 nanoseconds per operation.

Nominally, one operation is one @Benchmark invocation. Some annotations, like @OperationsPerInvocation may tell that a single @Benchmark invocation means N operations. Similarly, batched runs, e.g. via @Measurement(batchSize = N) may say that one operation contains N @Benchmark invocations.