goankur commented on code in PR #13572:
URL: https://github.com/apache/lucene/pull/13572#discussion_r1817385236
##########
lucene/benchmark-jmh/src/java/org/apache/lucene/benchmark/jmh/VectorUtilBenchmark.java:
##########
@@ -84,6 +91,76 @@ public void init() {
floatsA[i] = random.nextFloat();
floatsB[i] = random.nextFloat();
}
+ // Java 21+ specific initialization
+ final int runtimeVersion = Runtime.version().feature();
+ if (runtimeVersion >= 21) {
+ // Reflection based code to eliminate the use of Preview classes in JMH
benchmarks
+ try {
+ final Class<?> vectorUtilSupportClass =
VectorUtil.getVectorUtilSupportClass();
+ final var className =
"org.apache.lucene.internal.vectorization.PanamaVectorUtilSupport";
+ if (vectorUtilSupportClass.getName().equals(className) == false) {
+ nativeBytesA = null;
+ nativeBytesB = null;
+ } else {
+ MethodHandles.Lookup lookup = MethodHandles.lookup();
+ final var MemorySegment = "java.lang.foreign.MemorySegment";
+ final var methodType =
+ MethodType.methodType(lookup.findClass(MemorySegment),
byte[].class);
+ MethodHandle nativeMemorySegment =
+ lookup.findStatic(vectorUtilSupportClass, "nativeMemorySegment",
methodType);
+ byte[] a = new byte[size];
Review Comment:
Yes this is the setup code for the benchmark. We run setup once every
`iteration` for a total of `15` iterations across `3` forks (5 iterations per
fork) for each `size` being tested. Each fork is preceded by 3 warm-up
iterations.
So before **each** iteration we generate random numbers in range [0-127] in
two on-heap `byte[]`, allocate off-heap memory segments and populate them with
contents from `byte[]`. These off-heap memory segments are provided to
`VectorUtil.NATIVE_DOT_PRODUCT` method handle.
(Code snippet below for reference)
```
@Param({"1", "128", "207", "256", "300", "512", "702", "1024"})
int size;
@Setup(Level.Iteration)
public void init() {
...
}
```
> I wonder if we would see something different if we generated a large
number of vectors and randomized which ones we compare on each run. Also would
performance vary if the vectors are sequential in their buffer (ie vector 0
starts at 0, vector 1 starts at size...)
I guess the question you are hinting at is how does the performance vary
when the two candidate vectors are further apart in memory (L1 cache / L2 cache
/ L3 cache / Main-memory). Do the gains from native implementation become
insignificant with increasing distance ? Its an interesting question and I
propose that we add benchmark method(s) to answer them in a follow up PR. Does
that sound reasonable ?
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