1 Size-Based Scheduling Policies with Inaccurate Scheduling Information Dong Lu * , Huanyuan Sheng + , Peter A. Dinda * * Prescience Lab, Dept. of Computer Science + Dept. of Industrial Engineering & Management Science Northwestern University Evanston, IL 60201 USA
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Size-Based Scheduling Policies with Inaccurate Scheduling Information
Size-Based Scheduling Policies with Inaccurate Scheduling Information. Dong Lu * , Huanyuan Sheng + , Peter A. Dinda * * Prescience Lab, Dept. of Computer Science + Dept. of Industrial Engineering & Management Science Northwestern University Evanston, IL 60201 USA. Outline. - PowerPoint PPT Presentation
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Size-Based Scheduling Policies with Inaccurate Scheduling Information
Dong Lu*, Huanyuan Sheng+, Peter A. Dinda*
*Prescience Lab, Dept. of Computer Science+Dept. of Industrial Engineering & Management Science
Northwestern University
Evanston, IL 60201 USA
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Outline
• Review of size-based scheduling
• Motivation
• Simulation Setup
• Simulation Results
• New applications
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Non-size-based scheduling
• FCFS, PS, etc.
• FCFS: First Come First Serve– Intuitive– Easiest to implement
• PS: Processor Sharing– Fair: all jobs accept equal resources – Also easy to implement
Problem: Unaware of job size information, which results in big mean response time
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Review of size-based scheduling
• SRPT, FSP, etc.
• Utilize the job size (processing time, service time) information for scheduling– Optimal in mean response time– Fair?– Easy to implement?
We use Job Size to refer to the Processing Time (Service Time) of the job
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Shortest Remaining Processing Time (SRPT)
• Always serve the job with minimum remaining processing time first, Preemptive scheduling
• Yields minimum mean response time [Schrage, Operations Research, 1968]
• Performance gains of SRPT over PS do not usually come at the expense of large jobs, in other words, it is Fair for heavy-tail job size distribution [Bansal and Harchol-Balter, Sigmetrics ‘01]
• Easy to implement?– With accurate a priori job size information, YES
– Otherwise, NO
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Fair Sojourn Protocol (FSP)
• Combined SRPT with PS, preemptive scheduling
• Mean response time is close to that of SRPT; and more fair than PS [Friedman, et al, Sigmetrics ‘03]
• Easy to implement? – With accurate a priori job size information, YES– Otherwise, NO
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Motivation
• Size-based scheduling requires accurate knowledge of job sizes
• In practice, a priori job size information is not always available
• All the previous work assumes perfect knowledge of job sizes a priori
• How does performance depend on quality of job size information?
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Correlation
We study the performance of Size-based schedulers as a function of the correlation coefficient (Pearson’s R) between actual job sizes and estimated job sizes.
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Outline
• Review of size-based scheduling• Motivation• Simulation Setup• Simulation Results• New applications
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Simulation Setup: Trace generator
Trace Generator
Correlation (Pearson’s R)
Distribution A Distribution B
X Y1 1005 300. .. .. .
Correlated random pairs of X and Y• X has distribution A• Y has distribution B• X and Y are correlated to R
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Simulation Setup: Trace generator
• Algorithm: “Normal-To-Anything”– First developed by Cario and Nelson, on
INFORMS Journal on Computing 10, 1 (1998). – We simplified the algorithm and first introduced
it into the simulation studies of computer systems
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Scatter plot of example traces
R=0.13 R=0.78
Y
X
Y
X
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Simulation Setup: Performance metrics
• Performance metrics– Mean response time: Sojourn time, Turn-around time– Slowdown: the ratio of response time to its size.
Fairness metric
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Simulation Setup: Simulator
• Simulator– Written in C++– Supports M/G/1 and G/G/n/m queuing model
• Simulator validation– Little’s law– Repeat the simulations in the FSP paper [Friedman, et
al, Sigmetrics ‘03]
– Compare with available theoretical results [Bansal and Harchol-Balter, Sigmetrics ‘01]
For more details on the applications, please also see our short paper “Applications of SRPT Scheduling with Inaccurate Scheduling Information” in digital proceedings of MASCOTS ‘04 and a poster this evening.