The Impact of More Accurate Requested Runtimes on Production Job Scheduling Performance

The question of whether more accurate requested runtimes can significantly improve production parallel system performance has previously been studied for the FCFS-backfill scheduler, using a limited set of system performance measures. This paper examines the question for higher performance backfill policies, heavier system loads as are observed in current leading edge production systems such as the large Origin 2000 system at NCSA, and a broader range of system performance measures. The new results show that more accurate requested runtimes can improve system performance much more significantly than suggested in previous results. For example, average slowdown decreases by a factor of two to six, depending on system load and the fraction of jobs that have the more accurate requests. The new results also show that (a) nearly all of the performance improvement is realized even if the more accurate runtime requests are a factor of two higher than the actual runtimes, (b) most of the performance improvement is achieved when test runs are used to obtain more accurate runtime requests, and (c) in systems where only a fraction (e.g., 60%) of the jobs provide approximately accurate runtime requests, the users that provide the approximately accurate requests achieve even greater improvements in performance, such as an order of magnitude improvement in average slowdown for jobs that have runtime up to fifty hours.