On 01/03/2016 02:06 AM, Otmar Ertl wrote:
Am 03.01.2016 7:49 vorm. schrieb "Ole Ersoy" <ole.er...@gmail.com>:
Hi,
I ran another test using a single parallel loop for array based matrix
vector multiplication. Throughput almost tripled (Test pasted at bottom):
# Run complete. Total time: 00:13:24
Benchmark Mode Cnt Score Error
Units
MultiplyBenchmark.parallelMultiplication thrpt 200 2221.682 ±
48.689 ops/s
MultiplyBenchmark.singleThreadMultiplication thrpt 200 818.755 ±
9.782 ops/s
public class MultiplyBenchmark {
public static double[] multiplySingleThreaded(double[][] matrix,
double[] vector) {
return Arrays.stream(matrix)
.mapToDouble(row -> IntStream.range(0,
row.length).mapToDouble(col -> row[col]
* vector[col]).sum())
.toArray();
}
public static double[] multiplyConcurrent(double[][] matrix, double[]
vector) {
return Arrays.stream(matrix).parallel()
.mapToDouble(row -> IntStream.range(0,
row.length).mapToDouble(col -> row[col]
* vector[col]).sum())
.toArray();
}
@State(Scope.Thread)
public static class Matrix {
static int size = 10000;
static double[] vector = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
public static double[][] matrix = new double[size][10];
static {
for (int i = 0; i < size; i++) {
matrix[i] = vector.clone();
}
}
}
@Benchmark
public void singleThreadMultiplication(Matrix m) {
multiplySingleThreaded(m.matrix, m.vector);
}
@Benchmark
public void parallelMultiplication(Matrix m) {
multiplyConcurrent(m.matrix, m.vector);
}
}
Cheers,
Ole
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I am curious to see how this compares to simple for-loops which I can
imagine help the JIT compiler to do loop unrolling and to make use of
instruction-level parallelism.
According to the person that helped out initially on stackoverflow the stream
based loop is slightly faster. In his experiment the for loop took 100 seconds
and the stream did it in 89 seconds.
http://stackoverflow.com/questions/34519952/java-8-matrix-vector-multiplication
Not so sure about that though. Just read up on the below article and, like you
are saying, there are some tricks for making for loops very fast:
https://jaxenter.com/java-performance-tutorial-how-fast-are-the-java-8-streams-118830.html
Looking at the results per the article, sticking to primitives and for loops
can be wildly faster than streams. Looks like I'm going to have to follow her
advice and benchmark a lot :).
Cheers,
Ole
