Hi All,
I'm doing some work to profile Clojure's start-up performance so I can
figure out where the most bang for buck improvements could be made.
I wanted to verify that what I've done to instrument the call cost is
correct. I know benchmarking and am happy to take guidance from others.
In one of the classes I've created the following static atomic fields:
public static final AtomicLongArray latency = new AtomicLongArray(10000000);
public static final AtomicInteger index = new AtomicInteger(0);
Where latency is a preallocated array and the index is used to get the next
available slot in that array.
I'm instrumenting the call sites as follows:
public static Var intern(Namespace ns, Symbol sym, Object root){
long start = System.nanoTime();
// interesting work
Var v = intern(ns, sym, root, true);
long finish = System.nanoTime();
int i = RT.index.getAndIncrement(); // get next slot id
RT.latency.set(i, finish - start); // set the work time in the slot
return v;
}
Once the app shuts down I calculate the results as follows:
int count = RT.index.get();
System.out.println("Total Var.intern calls: " + count);
ArrayList<Long> al = new ArrayList<>();
for (int i = 0; i < count; i++) {
al.add(i, RT.latency.get(i));
}
List<Long> l = al.stream().sorted().collect(Collectors.toList());
Long total = al.stream().reduce((a, b) -> a + b).get() / 1_000_000;
double pctl99 = 0.99 * count;
double pctl50 = 0.5 * count;
System.out.println(
" Min: " + l.get(0) + "ns," +
" Median: " + l.get((int)pctl50) + "ns," +
" 99PCTL: " + l.get((int)pctl99) + "ns," +
" Max: " + l.get(count - 1) / 1_000_000 + "ms," +
" Total: " + total + "ms");
An example run yields the following:
Min: 162ns, Median: 907ns, 99PCTL: 30724ns, Max: 10ms, Total: 27ms
Is this an adequate way to capture the cost of calling a specific function?
Is there a way to improve the measurements (unfortunately JMH wouldn't be
straightforward to use at this point)?
Is there any obvious pitfalls I'm overlooking with this approach (e.g.
out-of-order execution, etc)?
Thanks in advance for any guidance.
Nathan
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