Tomcat Virtual Threads Performance

[Owner]

Hey Tomcat,

Andy here. I'm not sure if this is the place to ask this question, but I
wanted to check regarding performances of virtual threads vs using a
conventional worker thread pool.

I set up an endpoint with a CPU task of calculating factorials like the
below:

@GetMapping("/fullCPU")
    public void allCPU() throws InterruptedException {
        factorialCalculator();
    }

public void factorialCalculator() {
        int numberOfOperations = 35;
        BigInteger factorial = BigInteger.ONE;
        int n = 4000;
        for (int i = 1; i <= numberOfOperations; i++) {
            for (int j = 1; j <= n; j++) {
                factorial = factorial.multiply(BigInteger.valueOf(j));
            }
            factorial = BigInteger.ONE;
        }

When enabling virtual threads (using spring.virtual.threads.enabled with
Tomcat 10.1.33), the results I get are as follows. I utilise JMeter to do
stress testing -
[image: image.png]
Is there a reason why for CPU tasks, the performance for virtual threads is
so much worse? Theoretically both virtual threads and platform threads
should take the same amount of CPU time right?

Thank you!

Regards,
Andy