LM.Lecture6 - Distributed Operating Systems CS551 Colorado...

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Unformatted text preview: Distributed Operating Systems CS551 Colorado State University at Lockheed-Martin Lecture 6 -- Spring 2001 7 March 2001 CS-551, Lecture 6 2 CS551: Lecture 6 Topics Distributed Process Management (Chapter 7) Distributed Scheduling Algorithm Choices Scheduling Algorithm Approaches Coordinator Elections Orphan Processes Distributed File Systems (Chapter 8) Distributed Name Service Distributed File Service Distributed Directory Service 7 March 2001 CS-551, Lecture 6 3 Distributed Deadlock Prevention Assign each process a global timestamp when it starts No two processes should have same timestamp Basic idea: When one process is about to block waiting for a resource that another process is using, a check is made to see which has a larger timestamp (i.e. is younger). Tanenbaum, DOS (1995) 7 March 2001 CS-551, Lecture 6 4 Distributed Deadlock Prevention Somehow put timestamps on each process, representing creation time of process Suppose a process needs a resource already owned by another process Determine relative ages of both processes Decide if waiting process should Preempt , Wait , Die , or Wound owning process Two different algorithms 7 March 2001 CS-551, Lecture 6 5 Distributed Deadlock Prevention Allow wait only if waiting process is older Since timestamps increase in any chain of waiting processes, cycles are impossible Or allow wait only if waiting process is younger Here timestamps decrease in any chain of waiting process, so cycles are again impossible Wiser to give older processes priority 7 March 2001 CS-551, Lecture 6 6 Example: wait-die algorithm 54 79 79 54 Waits Holds resource Wants resource Wants resource Holds resource Dies 7 March 2001 CS-551, Lecture 6 7 Example: wound-wait algorithm 54 79 79 54 Preempts Holds resource Wants resource Wants resource Holds resource Waits 7 March 2001 CS-551, Lecture 6 8 Algorithm Comparison Wait-die kills young process When young process restarts and requests resource again, it is killed once more Less efficient of these two algorithms Wound-wait preempts young process When young process re-requests resource, it has to wait for older process to finish Better of the two algorithms 7 March 2001 CS-551, Lecture 6 9 Figure 7.7 The Bully Algorithm. (Galli, p. 169) 7 March 2001 CS-551, Lecture 6 10 Process Management in a Distributed Environment Processes in a Uniprocessor Processes in a Multiprocessor Processes in a Distributed System Why need to schedule Scheduling priorities How to schedule Scheduling algorithms 7 March 2001 CS-551, Lecture 6 11 Distributed Scheduling Basically resource management Want to distribute processing load among the processing elements in order to maximize performance Consider having several homogeneous processing elements on a LAN with equal average workloads Workload may still not be evenly distributed Some PEs may have idle cycles 7 March 2001...
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LM.Lecture6 - Distributed Operating Systems CS551 Colorado...

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