If you're able to multiplex a little bit (which most humans naturally do) the shape of the service time distribution does not matter as much as it may seem. (In

If you're able to multiplex a little bit (which most humans naturally do) the shape of the service time distribution does not matter as much as it may seem. (In the limit, perfect timesharing across tasks makes even the fattest of tails look M/M/k.) The more severe constraint is actually the first M. Fortunately, that holds true in practise very often.