Node.js setInterval CPU usage weirdness

high_cpu.js

var test = setInterval(function () {
  var a = 1;
}, 33.3); // the only difference is not using a float here. This file uses about 21% cpu on my vps

low_cpu.js

var test = setInterval(function () {
  var a = 1;
}, 33); // the only difference is not using a float here. This file uses basically 0.0% cpu on my vps

My test: 0.3%~1.4%(low_cpu.js), 2%~3.3%(high_cpu.js)