Selfish Jobs with Favorite Machines: Price of Anarchy vs Strong Price of Anarchy

TL;DR

This paper analyzes the efficiency loss in selfish machine scheduling, providing tight bounds on the price of anarchy and strong price of anarchy, and compares these concepts in related machine settings.

Contribution

It extends prior work by establishing exact bounds on the price of anarchy and strong price of anarchy for related machines, offering new insights into their relationship.

Findings

Strong price of anarchy is strictly smaller than 2 for related machines.

The setting is easier than unrelated machines in terms of equilibrium efficiency.

Provides tight bounds that quantitatively compare the two concepts.

Abstract

We consider the well-studied game-theoretic version of machine scheduling in which jobs correspond to self-interested users and machines correspond to resources. Here each user chooses a machine trying to minimize her own cost, and such selfish behavior typically results in some equilibrium which is not globally optimal: An equilibrium is an allocation where no user can reduce her own cost by moving to another machine, which in general need not minimize the makespan, i.e., the maximum load over the machines. We provide tight bounds on two well-studied notions in algorithmic game theory, namely, the price of anarchy and the strong price of anarchy on machine scheduling setting which lies in between the related and the unrelated machine case. Both notions study the social cost (makespan) of the worst equilibrium compared to the optimum, with the strong price of anarchy restricting to a stronger form of equilibria. Our results extend a prior study comparing the price of anarchy to the strong price of anarchy for two related machines (Epstein, Acta Informatica 2010), thus providing further insights on the relation between these concepts. Our exact bounds give a qualitative and quantitative comparison between the two models. The bounds also show that the setting is indeed easier than the two unrelated machines: In the latter, the strong price of anarchy is $2$, while in ours it is strictly smaller.