Process niceness (priority) setting has no effect on Linux

I wrote a test program which consists of just an infinite loop with some computations inside, and performs no I/O operations. I tried starting two instances of the program, one with a high niceness value, and the other with a low niceness value:

sudo nice -n 19 taskset 1 ./test
sudo nice -n -20 taskset 1 ./test

The taskset command ensures that both programs execute on the same core. Contrary to my expectation, top reports that both programs get about 50% of the computation time. Why is that? Does the nice command even have an effect?