1. P. (Saday) Sadayappan Ohio State University
Job Scheduling
P. (Saday) Sadayappan
Ohio State University

2. Problem Statement
Given a stream of parallel jobs and a set of computing resources, determine when and where to execute each job
In the form that the job scheduling problem is addressed at most supercomputer centers:
Homogeneous set of processors
Each job asks for a specific, fixed number of processors

3. Job Scheduling Today
Earliest job schedulers (Intel iPSC) used a simple FCFS strategy; low utilization (50%)
Back-filling was implemented at Argonne
Give an earliest-possible reservation to job at head of the queue, but allow a later arriving job to bypass it, if the reservation is not violated
Utilization improves to ~90%
Used at most production facilities today

4. Can Performance be Improved?
Metrics:
System Metric: Utilization
User Metrics: Response time (wait+run time), Slowdown (response-time/run-time)
Over a hundred papers published:
Focus mainly on improving user metrics: much greater potential for its improvement than utilization
Question: How important is it to squeeze an additional 5-10% utilization on a system that is already achieving over 85% utilization?

5. Improving Response Time
Question: How important is it to evaluate alternatives to standard back-fill scheduling, with a goal of improved user response-time?
Many studies have reported simulation studies showing significant improvement of slowdown or response-time with new schemes; but most production schedulers simply use aggressive back-fill. Why?

6. Possible Reasons for Non-Adoption
Academic studies do not model specific policy issues of a center, e.g. “good citizen rules,” multiple queues etc.
Most results are based on job log traces at Feitelson’s archive, with many logs from academic centers exhibiting low system utilization (< 70%).
Most studies report overall averages over entire trace: insufficient to assess impact of change:
E.g., using a Shortest-Job-First queue policy instead of the usual FCFS policy significantly improves overall average slowdown by a factor of 4; but increases response time for 24 hour jobs to 50 hours instead of 26 hours.

7. QoS for Job Scheduling Job schedulers do not provide QoS:
No response time guarantees
No equitable way of offering different service for urgent versus non-urgent jobs
Technical and Accounting issues:
Develop job schedulers that can do deadline-based scheduling
Develop accounting models to charge based on urgency of job:
Charge = f1(resource-usage) + f2(wait-time-limit)
Question: How desirable is it to develop job schedulers with QoS functionality?

8. Questions?