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Unformatted text preview: 14-114-1Time and SchedulingOutline of material in this set:Time measures.Accounting for CPU time,e.g.50% idle.Performance measures.Measures of CPU performance.Task states.Label indicating a tasks needs.Scheduling data.Information OS uses to schedule tasks.Scheduling events.Actions which cause the OS to stop one task and start another.Scheduling algorithms.How the OS chooses which task to run.14-1EE 4770 Lecture Transparency. Formatted 13:27, 23 December 1997 from lsli14.14-114-214-2Time MeasuresAt any time a CPU will be doing one of three things:Running a task in user mode,running in privileged mode,idle (no tasks to run).For an understood interval,T, lettu(T) denote time CPU inusermode,tp(T) denote time CPU inprivilegedmode,ti(T) denote time CPU isidle.The duration of the interval,t(T), is the sum of these. . .t(T) =tu(T) +ts(T) +ti(T).Tsometimes omitted for brevity.14-2EE 4770 Lecture Transparency. Formatted 13:27, 23 December 1997 from lsli14.14-214-314-3Performance MeasuresSeveral different measures of performance are used.Each measures a different aspect of performance.Utilization[of the CPU].How efficiently CPU time is being used.Throughput[of the system].What rate (e.g.tasks/hour) work is getting done.Turnaround time[of a particular or average task].The time to complete an individual task. . .. . .or the average time to complete a task.Response time[of a particular or average task].The time between a particular event and response.(Usually the task responding to user input.)14-3EE 4770 Lecture Transparency. Formatted 13:27, 23 December 1997 from lsli14.14-314-414-4UtilizationThe utilization of a CPU overT, denotedU(T) is given by:U(T) =tu(T) +tp(T)t(T),wheretu(T) is the user time over intervalT,tp(T) is the privileged time over intervalT,andt(T) is the total duration of intervalT.Utilization is in the range [0,1].Accountants want utilization to be high. . .. . .users want it to be low (when they run their tasks).ThroughputLetn(T) be the number of tasks which complete in time periodT.Then throughput is given by(T) =n(T)t(T).The popular SPECrate benchmarks measure throughput.14-4EE 4770 Lecture Transparency. Formatted 13:27, 23 December 1997 from lsli14.14-414-514-5Turnaround TimeLet a task be submitted att1.Let the task be completed att2.Then the turnaround time for the task ist2-t1.Users want turnaround time to be short.When utilization is low, turnaround time is usually short.The SPECint and SPECfp benchmarks measure turnaround time onan unloaded system (in contrast to the SPECrate benchmarks).14-5EE 4770 Lecture Transparency. Formatted 13:27, 23 December 1997 from lsli14.14-514-614-6Response TimeResponse time defined for aneventandresponse....
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This note was uploaded on 11/28/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.
- Fall '99