CPT U3

RESEARCH ON SCHEDULING
1. Describe the objectives of scheduling. [4]
The objectives of scheduling are: 1) Fairness. Fairness is important under all circumstances. A scheduler makes sure that each process gets its fair share of the CPU and no process can suffer indefinite postponement. Note that giving equivalent or equal time is not fair. 2) Policy Enforcement. The scheduler has to make sure that system's policy is enforced. For example, if the local policy is safety then the safety control processes must be able to run whenever they want to, even if it means delay in payroll processes. 3) Efficiency. Scheduler should keep the system (or in particular CPU) busy every percent of the time when possible. If the CPU and all the Input/output devices can be kept running all the time, more work gets done per second than if some components are idle. 4) Response Time. A scheduler should minimize the response time for interactive user.
RESOURCE: http://www.personal.kent.edu/~rmuhamma/OpSystems/Myos/cpuScheduling.htm
2. State and describe 3 methods of scheduling. [6]
There are three methods of scheduling. 1) Long- term-scheduler. The long-term scheduling controls the degree of multiprogramming and decides on which job or jobs to accept and turn into processes. The more jobs created, the smaller the percentage of time that each process can take to be executed; so long-term scheduling may limit the degree of multiprogramming to provide satisfactory services to the current set of processes. 2) Medium-term scheduler. This determines which processes suspended and resumed." It swaps processes out to improve job mix". (William Buchanan, Distributed systems and Networks, 71). 3) Short-term scheduler. Short-term scheduling is concerned with the allocation of processor time to processes in order to meet some pre-defined system performance objectives. The task of short-term scheduling is to select specific resources and exact times for all activities of the orders to be scheduled.
References:
1. William Buchanan, Distributed systems And Networks, Pg 71-88, Napier University. McGraw-Hill International (UK) Limited
2. William Stallings, Operating Systems Internals and Design Principles (Characteristics of Various Scheduling policies Table 9:3, pg. 387)
3. William S. Davis, Operating Systems, A Systematic View,3rd Edition, Miami University Oxford, Ohio, Addison-Wesley Publishing Company
4. http://www-courses.cs.uiuc.edu/~cs323/reviews/cs323_summ02_midterm1.pdf
5. http://www.cs.nott.ac.uk/~gxk/courses/g53ops/Scheduling/sched09-mlfqs.html
6. http://www.cs.virginia.edu/~cl7v/Papers/rtsj.pdf
7. http://www.ecst.csuchico.edu/~beej/guide/win95sch.html
8. http://www.dynamicdrive.com/dynamicindex11/highlighttable.htm
9. http://www.dynamicdrive.com/dynamicindex3/index.html
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