直接字节缓冲器相对读取性能与绝对读取性能
2022-09-04 02:07:16
当我测试直接java.nio.ByteBuffer的读取性能时，我注意到绝对读取平均比相对读取快2倍。此外，如果我比较相对读取与绝对读取的源代码，代码几乎是相同的，除了相对读取维护和内部计数器。我想知道为什么我看到如此大的速度差异？
以下是我的JMH基准测试的源代码：
public class DirectByteBufferReadBenchmark {
private static final int OBJ_SIZE = 8 + 4 + 1;
private static final int NUM_ELEM = 10_000_000;
@State(Scope.Benchmark)
public static class Data {
private ByteBuffer directByteBuffer;
@Setup
public void setup() {
directByteBuffer = ByteBuffer.allocateDirect(OBJ_SIZE * NUM_ELEM);
for (int i = 0; i < NUM_ELEM; i++) {
directByteBuffer.putLong(i);
directByteBuffer.putInt(i);
directByteBuffer.put((byte) (i & 1));
}
}
}
@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public long testReadAbsolute(Data d) throws InterruptedException {
long val = 0l;
for (int i = 0; i < NUM_ELEM; i++) {
int index = OBJ_SIZE * i;
val += d.directByteBuffer.getLong(index);
d.directByteBuffer.getInt(index + 8);
d.directByteBuffer.get(index + 12);
}
return val;
}
@Benchmark
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.SECONDS)
public long testReadRelative(Data d) throws InterruptedException {
d.directByteBuffer.rewind();
long val = 0l;
for (int i = 0; i < NUM_ELEM; i++) {
val += d.directByteBuffer.getLong();
d.directByteBuffer.getInt();
d.directByteBuffer.get();
}
return val;
}
public static void main(String[] args) throws Exception {
Options opt = new OptionsBuilder()
.include(DirectByteBufferReadBenchmark.class.getSimpleName())
.warmupIterations(5)
.measurementIterations(5)
.forks(3)
.threads(1)
.build();
new Runner(opt).run();
}
}
这些是我的基准测试运行的结果：
Benchmark Mode Cnt Score Error Units
DirectByteBufferReadBenchmark.testReadAbsolute thrpt 15 88.605 ± 9.276 ops/s
DirectByteBufferReadBenchmark.testReadRelative thrpt 15 42.904 ± 3.018 ops/s
该测试在MacbookPro（2.2GHz Intel Core i7，16Gb DDR3）和JDK 1.8.0_73上运行。
更新
我用JDK 9-ea b134运行相同的测试。两个测试都显示速度提高了约10%，但两者之间的速度差仍然相似。
# JMH 1.13 (released 45 days ago)
# VM version: JDK 9-ea, VM 9-ea+134
# VM invoker: /Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/bin/java
# VM options: <none>
Benchmark Mode Cnt Score Error Units
DirectByteBufferReadBenchmark.testReadAbsolute thrpt 15 102.170 ± 10.199 ops/s
DirectByteBufferReadBenchmark.testReadRelative thrpt 15 45.988 ± 3.896 ops/s
