07、Java 19 新特性 - Vector API（第四次预览）
新的Vector API与java.util.Vector类没有关系。事实上，它是关于数学向量计算的新 API 及其与现代SIMD（单指令-多数据）CPU的映射。
详见：[JDK Enhancement Proposal 426][]
Java Vector API的使用测试
Vector API
Vector API 是Java18开始引入的一个项目（JEP 417），通过引入该API来表达向量运算，该计算在运行时可靠地编译为支持的CPU架构上的最优向量指令，从而实现优于等效标量计算的性能。
首先，简单说明一下矢量运算的基本概念，你可以简单理解为正常情况下我们使用的计算机是64位的，但是有时计算机可能需要同时处理多项任务时就意味着需要更多的位数，这其中可以通过以上链接了解到关于预测寄存器和矢量寄存器相关知识，其中矢量寄存器的位数可以在128位到2048位不等，比如我的计算机的SVE寄存器位256位，那我一次可以处理256/32(int所占位数)=8个数据，具体见下列代代码。
void daxpy (double *x, double *y, double a, int n){
for (int i= 0; i < n; i++)
y[i] = a*x [i] + y[i];
}
- p表示预测寄存器
- z表示SVE寄存器
关于Vector API的部分说明：
1、 只支持x64和AArch64架构的CPU；
2、 目前只作用与C2编译器；
编写测试代码
该项目代码使用JMH进行测试，需要导入以下依赖
<!-- https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-generator-annprocess -->
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-generator-annprocess</artifactId>
<version>1.35</version>
<scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-core -->
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<version>1.35</version>
<scope>provided</scope>
</dependency>
//VM Options: --add-modules jdk.incubator.vector
import jdk.incubator.vector.IntVector;
import jdk.incubator.vector.VectorSpecies;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.results.format.ResultFormatType;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;
import java.io.File;
import java.io.IOException;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Warmup(iterations = 3,time = 1,timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 3,time = 1,timeUnit = TimeUnit.SECONDS)
@Fork(1)
public class JMH {
private int[] nums;
@Param({
"100",
"1000",
"10000",
"100000",
"1000000",
"10000000",
"100000000",
"250000000"
})
int size;
@Setup
public void setup(){
nums = new int[size];
}
@Benchmark
public int[] StreamComputation(){
int[] result = new int[size];
Arrays.parallelSetAll(result, i -> (nums[i] * i + nums[i] * nums[i])*-1);
return result;
}
@Benchmark
public void ParallelComputation() throws InterruptedException {
int[] result = new int[size];
CountDownLatch count = new CountDownLatch(8);
for (int i = 0; i < 8; i++) {
final int start = i;
new Thread(()->{
for (int j = start; j < nums.length; j += 8) {
result[j] = (nums[j]*j+nums[j]*nums[j])*-1;
}
count.countDown();
}).start();
}
count.await();
}
@Benchmark
public int[] Vector128Computation(){
int[] result = new int[size];
VectorSpecies<Integer> species = IntVector.SPECIES_128;
int loop = species.loopBound(nums.length);
int i = 0;
for (; i < loop; i += species.length()) {
IntVector va = IntVector.fromArray(species,nums,i);
IntVector vb = IntVector.fromArray(species,nums,i);
IntVector vc = va.mul(va)
.add(vb.mul(vb))
.neg();
vc.intoArray(result,i);
}
for (; i < nums.length; i++) {
result[i] = nums[i]*i+nums[i]*nums[i]*(-1);
}
return result;
}
@Benchmark
public int[] Vector256Computation(){
int[] result = new int[size];
VectorSpecies<Integer> species = IntVector.SPECIES_256;
int loop = species.loopBound(nums.length);
int i = 0;
for (; i < loop; i += species.length()) {
IntVector va = IntVector.fromArray(species,nums,i);
IntVector vb = IntVector.fromArray(species,nums,i);
IntVector vc = va.mul(va)
.add(vb.mul(vb))
.neg();
vc.intoArray(result,i);
}
for (; i < nums.length; i++) {
result[i] = nums[i]*i+nums[i]*nums[i]*(-1);
}
return result;
}
@Benchmark
public int[] Vector512Computation(){
int[] result = new int[size];
VectorSpecies<Integer> species = IntVector.SPECIES_512;
int loop = species.loopBound(nums.length);
int i = 0;
for (; i < loop; i += species.length()) {
IntVector va = IntVector.fromArray(species,nums,i);
IntVector vb = IntVector.fromArray(species,nums,i);
IntVector vc = va.mul(va)
.add(vb.mul(vb))
.neg();
vc.intoArray(result,i);
}
for (; i < nums.length; i++) {
result[i] = nums[i]*i+nums[i]*nums[i]*(-1);
}
return result;
}
@Benchmark
public int[] defaultComputation(){
int[] result = new int[size];
for (int i = 0; i < nums.length; i++) {
result[i] = (nums[i]*i+nums[i]*nums[i])*-1;
}
return result;
}
public static void main(String[] args) throws RunnerException, IOException {
Options opts = new OptionsBuilder()
.include(JMH.class.getSimpleName())
.resultFormat(ResultFormatType.JSON)
.output(new File("jmh.log").getCanonicalPath())
.build();
new Runner(opts).run();
}
}
测试结果
Benchmark (size) Mode Cnt Score Error Units
JMH.ParallelComputation 100 avgt 3 29.676 ± 3.856 us/op
JMH.ParallelComputation 1000 avgt 3 32.549 ± 28.265 us/op
JMH.ParallelComputation 10000 avgt 3 45.063 ± 9.727 us/op
JMH.ParallelComputation 100000 avgt 3 219.920 ± 37.503 us/op
JMH.ParallelComputation 1000000 avgt 3 2070.604 ± 700.193 us/op
JMH.ParallelComputation 10000000 avgt 3 15660.505 ± 2796.283 us/op
JMH.ParallelComputation 100000000 avgt 3 256957.510 ± 1039982.820 us/op
JMH.ParallelComputation 250000000 avgt 3 652928.650 ± 175108.941 us/op
JMH.StreamComputation 100 avgt 3 8.579 ± 1.535 us/op
JMH.StreamComputation 1000 avgt 3 9.602 ± 0.726 us/op
JMH.StreamComputation 10000 avgt 3 20.908 ± 3.043 us/op
JMH.StreamComputation 100000 avgt 3 78.725 ± 15.190 us/op
JMH.StreamComputation 1000000 avgt 3 1080.335 ± 444.759 us/op
JMH.StreamComputation 10000000 avgt 3 7989.456 ± 3523.566 us/op
JMH.StreamComputation 100000000 avgt 3 77524.201 ± 30073.807 us/op
JMH.StreamComputation 250000000 avgt 3 192820.889 ± 7839.996 us/op
JMH.Vector128Computation 100 avgt 3 0.061 ± 0.007 us/op
JMH.Vector128Computation 1000 avgt 3 0.643 ± 0.048 us/op
JMH.Vector128Computation 10000 avgt 3 6.323 ± 0.553 us/op
JMH.Vector128Computation 100000 avgt 3 59.549 ± 34.958 us/op
JMH.Vector128Computation 1000000 avgt 3 1174.302 ± 404.046 us/op
JMH.Vector128Computation 10000000 avgt 3 8473.528 ± 1039.583 us/op
JMH.Vector128Computation 100000000 avgt 3 82410.628 ± 19711.603 us/op
JMH.Vector128Computation 250000000 avgt 3 205339.393 ± 52689.755 us/op
JMH.Vector256Computation 100 avgt 3 0.073 ± 0.012 us/op
JMH.Vector256Computation 1000 avgt 3 0.591 ± 0.034 us/op
JMH.Vector256Computation 10000 avgt 3 5.700 ± 1.486 us/op
JMH.Vector256Computation 100000 avgt 3 56.608 ± 13.098 us/op
JMH.Vector256Computation 1000000 avgt 3 1139.838 ± 273.834 us/op
JMH.Vector256Computation 10000000 avgt 3 8321.221 ± 4300.157 us/op
JMH.Vector256Computation 100000000 avgt 3 82288.278 ± 45482.083 us/op
JMH.Vector256Computation 250000000 avgt 3 204230.229 ± 89249.522 us/op
JMH.Vector512Computation 100 avgt 3 0.587 ± 0.056 us/op
JMH.Vector512Computation 1000 avgt 3 6.084 ± 1.852 us/op
JMH.Vector512Computation 10000 avgt 3 64.068 ± 2.557 us/op
JMH.Vector512Computation 100000 avgt 3 612.263 ± 93.553 us/op
JMH.Vector512Computation 1000000 avgt 3 6541.734 ± 5697.026 us/op
JMH.Vector512Computation 10000000 avgt 3 61163.729 ± 11045.924 us/op
JMH.Vector512Computation 100000000 avgt 3 767615.083 ± 241938.527 us/op
JMH.Vector512Computation 250000000 avgt 3 1632611.033 ± 1793126.085 us/op
JMH.defaultComputation 100 avgt 3 0.105 ± 0.008 us/op
JMH.defaultComputation 1000 avgt 3 0.936 ± 0.059 us/op
JMH.defaultComputation 10000 avgt 3 9.323 ± 0.311 us/op
JMH.defaultComputation 100000 avgt 3 77.149 ± 11.756 us/op
JMH.defaultComputation 1000000 avgt 3 1308.792 ± 828.180 us/op
JMH.defaultComputation 10000000 avgt 3 9623.205 ± 3032.074 us/op
JMH.defaultComputation 100000000 avgt 3 92491.573 ± 17694.014 us/op
JMH.defaultComputation 250000000 avgt 3 225411.133 ± 18094.859 us/op
