09-04-2012, 01:04 PM
Common Approaches to Real-Time Scheduling
sched_approaches.pdf (Size: 174.19 KB / Downloads: 171)
Clock-driven (time-driven) schedulers
– Scheduling decisions are made at specific time instants, which
are typically chosen a priori.
Priority-driven schedulers
– Scheduling decisions are made when particular events in the
system occur, e.g.
• a job becomes available
• processor becomes idle
Clock-Driven (Time-Driven) -- Overview
Scheduling decision time: point in time when scheduler decides
which job to execute next.
• Scheduling decision time in clock-driven schedulers is defined a
priori.
• For example: Scheduler periodically wakes up and generates a
portion of the schedule.
Priority-Driven -- Overview
• Basic rule: Never leave processor idle when there is work to be
done. (such schedulers are also called work conserving)
• Based on list-driven, greedy scheduling.
• Examples: FIFO, LIFO, SET, LET, EDF.
• Possible implementation of preemptive priority-driven scheduling:
– Assign priorities to jobs.
– Scheduling decisions are made when
• Job becomes ready
• Processor becomes idle
• Priorities of jobs change
– At each scheduling decision time, choose ready task with
highest priority.