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Unit 5: Scheduling

Figure 5.10: Multi-processor Queue Notes
RQ0 Release
Admit
Processor

RQ1 Release
Processor

RQ2 Release
Processor

5.7 Thread Scheduling

The main approaches of threading scheduling are:
1. Load sharing
2. Gang scheduling

3. Dedicated processor assignment
4. Dynamic scheduling

5.7.1 Load Sharing

Processes are not assigned to a particular processor. A global queue of ready threads is maintained
and each processor, when idle select a thread from the queue.

There are three versions of load sharing are these are:
1. First come fi rst served
2. Smallest number of threads fi rst
3. Preemptive smallest number of threads fi rst
1. First come fi rst served: when a job arrives each of its threads is placed consecutively at the
end of the shared queue. When a processor becomes idle it picks the next ready thread,
which it executes until completion or blocking.

2. Smallest number of thread fi rst: The shared ready queue is organized as a priority queue
with highest priority given to threads from jobs with the smallest number of unscheduled
threads. Jobs of equal priority are ordered according to which job arrives fi rst.

3. Preemptive smallest number of threads fi rst: Highest is given to jobs with the smallest
number of incomplete threads.

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