udev monitor is slow without polling

I tried udev as recommended (udevadm monitor). The VGA-Plug is reported after approx. two seconds. If I poll开发者_StackOverflow中文版 it, the change is reported almost instantly. What happens here?

If the polling was constant there would be much wasted CPU time, and the event timing would be skewed in the log output. When you manually poll, its occurring instantly, no timeout.