Approximating total flow time on parallel machines
STOC '97 Proceedings of the twenty-ninth annual ACM symposium on Theory of computing
Minimizing the flow time without migration
STOC '99 Proceedings of the thirty-first annual ACM symposium on Theory of computing
Approximation schemes for preemptive weighted flow time
STOC '02 Proceedings of the thiry-fourth annual ACM symposium on Theory of computing
SODA '06 Proceedings of the seventeenth annual ACM-SIAM symposium on Discrete algorithm
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We consider the problem of minimizing the total flow time on multiple machines with preemption, where the flow time of a job is the time spent since it arrives until it finishes. Our main result is a quasi-polynomial time approximation scheme for a constant number of machines (m). The result also extends to total weighted flow time where either the job weights or the job sizes are polynomially bounded by the number of jobs (n). We also show that the dependence on m cannot be substantially improved. In particular, obtaining an O(1) approximation for the weighted case (even when all weights and sizes are polynomially bounded by n) by an algorithm with running time npolylog(n,m) would imply that NP ⊂ DTIME(npolylog(n)).