Basic Concept: Tickets Represent Your Share

Underlying lottery scheduling is one very basic concept: tickets, which are used to represent the share of a resource that a process (or user or whatever) should receive. The percent of tickets that a process has represents its share of the system resource in question.

Example

Let’s look at an example. Imagine two processes, $A$ and $B$, and further that $A$ has 75 tickets while $B$ has only 25. Thus, what we would like is for $A$ to receive 75% of the CPU and $B$ the remaining 25%.

Lottery scheduling achieves this probabilistically (but not deterministically​) by holding a lottery every so often (say, every time slice). Holding a lottery is straightforward: the scheduler must know how many total tickets there are (in our example, there are 100). The scheduler then picks a winning ticket, which is a number from 0 to 99.