Lottery scheduling

Lottery scheduling is a probabilistic scheduling algorithm for processes in an operating system. Processes are each assigned some number of lottery tickets, and the scheduler draws a random ticket to select the next process. The distribution of tickets need not be uniform; granting a process more tickets provides it a relative higher chance of selection. This technique can be used to approximate other scheduling algorithms, such as Shortest job next and Fair-share scheduling.

Lottery scheduling solves the problem of starvation. Giving each process at least one lottery ticket guarantees that it has non-zero probability of being selected at each scheduling operation.

Implementation

Implementations of lottery scheduling should take into consideration that there could be billions of tickets distributed among a large pool of threads. To have an array where each index represents a ticket, and each location contains the thread corresponding to that ticket, may be highly inefficient. Lottery scheduling can be preemptive or non-preemptive.

External links

• Lottery Scheduling: Flexible Proportional-Share Resource Management by Carl A. Waldspurger and William E. Weihl. The 1994 Operating Systems Design and Implementation conference (OSDI '94). November, 1994. Monterey, California.
• Lottery and Stride Scheduling: Flexible Proportional-Share Resource Management by Carl A. Waldspurger. Ph.D. dissertation, Massachusetts Institute of Technology. September 1995.
• Operating Systems: Three Easy Pieces by Remzi H. Arpaci-Dusseau and Andrea C. Arpaci-Dusseau. Arpaci-Dusseau Books, 2014. Relevant chapter: Proportional-Share Scheduling.
• Implementing Lottery Scheduling - Matching the Specialization in Traditional Schedulers - Paper by David Petrou et al.
• Stochastic priority-based task Scheduler by Robert V. Welland and Walter R. Smith. United States Patent Number US 5247677 A