Comparisons of service disciplines in a tandem queueing network with real time constraints

Soft real-time environments consist of jobs that must receive service within a particular time interval. If service for a specific job is not completed by the end of its time interval, it is said to be lost; in addition, the computation time expended on the job is wasted, and any further computation for the job is discontinued. The goal of a system designer is to provide an environment that minimizes the number of jobs that are lost. If a parallel environment is available, the system designer has two options: Allow each processor to execute a job individually, or let multiple processors cooperate in executing a job. This article shows, for two classes of static allocation policies, that simple comparative analytical models may be used to indicate which option minimizes the number of lost jobs, as a function of workload intensity. The first class of policies, called equal partitions, statically decomposes the system into equal-size sets of processors and executes one job per partition. These policies are frequently employed in other contexts. The second class of policies, called two partitions, statically partitions the processors into two sets, not necessarily of the same size. Surprisingly, it is observed mathematically that even for statistically identical jobs, this class of policies is superior to equal partitions under certain loadings. The analysis is validated experimentally with a workload executed on a 16-node iPSC/2 hypercube. >

Static processor allocation in a soft real-time multiprocessor environment

: Our research funded under ONR contract N00014-87-K-0796 can be broadly divided into five areas: (1) design and analysis of deadline based scheduling policies, (2) design and evaluation of high performance and fault tolerant disk architectures for real-time systems, (3) design and evaluation of scheduling policies for real-time tasks with incremental-value-with-increased- execution-time characteristics, (4) reliability and testing of real-time systems, (5) scheduling for real-time parallel processing systems These topics will be the subject of the reminder of the technical section Additional details of our work can be found in the cited technical papers and reports

Design and Analysis of Scheduling Policies for Real-Time Computer Systems

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0269964800003375

Optimality Aspects of Greedy Schemes in Parallel Processing of Random Graph-Structured Jobs

WE CONSIDER PARALLEL EXECUTION OF STRUCTURED JOBS WITH REAL TIME CON- STRAINTS IN (POSSIBLY HETEROGENEOUS) MULTIPROCESSOR SYSTEMS. A JOB IS COM- POSED OF A SET OF TASKS AND A PARTIAL ORDER SPECIFYING THE PRECEDENCE CON- STRAINTS BETWEEN THE TASKS. THE TASK PROCESSING TIMES ARE RANDOM VARIABLES WITH KNOWN PROBABILITY DISTRIBUTION FUNCTIONS. THE INTERARRIVAL TIME OF THE JOBS ARE ALSO RANDOM VARIABLES WITH ARBITRARY DISTRIBUTIONS. THE REAL TIME CONSTRAINTS ARE SPECIFIED BY REFERENCE TIMES, ALSO CALLED SOFT REAL-TIME DEADLINES. IN THE DISCUSSION WE ASSUME FIRST THAT ALL THE JOBS HAVE THE SAME TASK GRAPH, I.E, THE SAME TASK SET AND THE SAME PARTIAL ORDER. WE ASSUME THAT THERE IS A PREDEFINED MAPPING FROM THE SET OF TASKS ONTO THE SET OF TASKS ONTO THE SET OF MACHINES, IDENTICAL FOR ALL JOBS, THAT ALLO- CATES TASKS TO MACHINES. WE FOCUS ON DYNAMIC SCHEDULING POLICIES WHICH DO NOT USE INFORMATION ON THE PROCESSING TIMES OF THE TASKS TO BE SCHEDULED. THE POLICIES CAN BE NON-PREEMPTIVE OR PREEMPTIVE-RESUME. FOR NON-PREEMPTIVE POLICIES, WE ASSUME THAT TASKS PROCESSING TIMES ARE INDEPENDENTLY AND IDEN- TICALLY DISTRIBUTED, WHEREAS FOR THE PREEMPTIVE ONES, WE ASSUME THAT THEY ARE INDEPENDENTLY AND IDENTICALLY DISTRIBUTED AND COME FROM SOME SPECIFIC DISTRIBUTIONS. SOME OF THE RESULTS THAT ARE OBTAINED GENERALIZE TO THE CASE WHERE JOBS HAVE A RANDOM STRUCTURE. THIS MORE DIFFICULT CASE IS TREATED AT THE END OF THE PAPER.

F. Baccelli

Papers

Optimal Scheduling of Parallel Processing Systems with Real-Time