Hello,
-XX:TieredStopAtLevel=1 flag is often used in some applications (e.g. Spring
Boot based) to reduce start-up time.
With this flag I've spotted huge performance degradation of Array::newInstance
comparing to plain constructor call.
I've used this benchmark
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class ArrayInstantiationBenchmark {
@Param({"10", "100", "1000"})
private int length;
@Benchmark
public Object newInstance() {
return Array.newInstance(Object.class, length);
}
@Benchmark
public Object constructor() {
return new Object[length];
}
}
On C2 (JDK 11) both methods perform the same:
Benchmark (length) Mode Cnt Score Error
Units
ArrayInstantiationBenchmark.constructor 10 avgt 50 11,557 ± 0,316
ns/op
ArrayInstantiationBenchmark.constructor 100 avgt 50 86,944 ± 4,945
ns/op
ArrayInstantiationBenchmark.constructor 1000 avgt 50 520,722 ± 28,068
ns/op
ArrayInstantiationBenchmark.newInstance 10 avgt 50 11,899 ± 0,569
ns/op
ArrayInstantiationBenchmark.newInstance 100 avgt 50 86,805 ± 5,103
ns/op
ArrayInstantiationBenchmark.newInstance 1000 avgt 50 488,647 ± 20,829
ns/op
On C1 however there's a huge difference (approximately 8 times!) for length =
10:
Benchmark (length) Mode Cnt Score Error
Units
ArrayInstantiationBenchmark.constructor 10 avgt 50 11,183 ± 0,168
ns/op
ArrayInstantiationBenchmark.constructor 100 avgt 50 92,215 ± 4,425
ns/op
ArrayInstantiationBenchmark.constructor 1000 avgt 50 838,303 ± 33,161
ns/op
ArrayInstantiationBenchmark.newInstance 10 avgt 50 86,696 ± 1,297
ns/op
ArrayInstantiationBenchmark.newInstance 100 avgt 50 106,751 ± 2,796
ns/op
ArrayInstantiationBenchmark.newInstance 1000 avgt 50 840,582 ± 24,745
ns/op
Pay attention that performance for length = {100, 1000} is almost the same.
I suppose it's a bug somewhere on VM because both methods just allocate memory
and do zeroing elimination and subsequently there shouldn't be such a huge
difference between them.
Sergey Tsypanov
