JIT Fun Part 1: Quick JIT visualisation of tiered compliation

See the following code:

	public static void main(String... args) {
	int count = 0;
	for (int i =0; i <1000; i++) {
	long startTime = System.nanoTime();
	for (int j = 0; j < 1000; j ++) {
	count += j;
	}
	long endtime = System.nanoTime();
	System.out.printf("%d\n", endtime - startTime);
	}
	System.out.println(count);
	}

view raw runMainLotsOfTimes.java hosted with ❤ by GitHub

It's not doing anything exciting, just running the same inner loop 1000 times.

I have taken those times and put them in a file called 'output.txt'.

See the following python function which reads in the numbers from output.txt and plots them on a graph:

	import matplotlib.pyplot as plt
	ys = []
	with open('output.txt') as fp:
	content = fp.readlines()
	for line in content:
	ys.append(int(line.strip()))
	plt.plot(ys)
	plt.ylabel("Time (ns)")
	plt.show()

view raw plotOnGraph.py hosted with ❤ by GitHub

Here is the graph that it produces:

At first the code is running in the interperter, then the C1 JIT, then it settles into the C2 JIT. A couple of spikes probably indicate GC.