1. MULTIPROCESSOR SYSTEMS www.eITnotes.com

2. OUTLINE  Coordinated job Scheduling  Separate Systems  Homogeneous Processor Scheduling  Master/Slave Scheduling www.eITnotes.com

3. MULTIPROCESSOR SYSTEMS  To enhance throughput, reliability, computing power and parallelism, additional processors can be added to systems.  In early multiprocessor systems the additional processors had specialized functions e.q I/O channels.  Later, multiprocessing systems evolved to include the concept of one large CPU and several processors.  These processors may perform quite sophisticated tasks, such as running a display. www.eITnotes.com

4.  A more common type of multiprocessing is a system having two or more processors having equal power  Example HIS 6180 IBM 158MP 168 MP www.eITnotes.com

5.  There are various ways to connect and operate a multiprocessor system Coordinated job Scheduling Separate Systems Homogeneous Processor Scheduling Master/Slave Scheduling  These techniques differ in degree of scheduling sophistication. www.eITnotes.com

6. SEPARATE SYSTEMS  Some systems, for example, IBM System/360 model, can be logically subdivided into two or more separate systems, each with one processor, some main memory, and other devices.  This is just like having two or more separate computing systems, all in the same room.  The advantage of this organization is that processors, memories and I/O devices can be easily, though manually, switched.  This configuration flexibility is useful if there are some jobs that requires the full complement of memory and/or I/O devices resources.  Alternatively, if one processor is being repaired, all the other resources can be pooled into one large system rather than be allowed to sit. www.eITnotes.com

7. COORDINATED JOB SCHEDULING  A variation on the separate system multiprocessor technique is called coordinated job scheduling.  Which is also called Loosely coupled multiprocessing.  In this, each processor is associated with a separate system. When a job is arrives, it may be assigned to any system.  The assignments of a job to a system may be based on a variety of requirements and policies, such as assigning the job to the system with the lightest load.  To accomplish this balancing, all job scheduling must be coordinated. This may be done manually, by a special purpose computer ( Lawrence Radiation Laboratory) or by one of the actual processing system (as done on IBM’s OS/VS-2 Job entry system). www.eITnotes.com

8. MASTER/SLAVE SCHEDULING  The permanent assignment of the job to a system in the coordinate job scheduling technique, cannot handle short term balancing of resource demand.  In general multiprocessor system all memory and I/O devices are accessible to all processors.  Memory and I/O devices are assigned to the processes, not to the processors.  This is called the Tightly coupled multiprocessing.  The processors are assigned to execute processes as determined by the process scheduler – except that there are now multiple processors available for assignment. www.eITnotes.com

9.  In master/slave scheduling technique, one processor maintains the status of all processes in the system and schedule the work of all the slave processors.  For example, the master processor selects a process to be run, finds the available processor and issue a start processor instruction.  The slave processor starts execution at the indicated memory location. When the slave encounters an exceptional event, such as an I/O request, it generates an interrupt to the master processor and stops to await further order.  Note that different slave processors may be assigned to a process at a different time. www.eITnotes.com

10.  Following example shows In which manner multiple processors may be used for multiprogramming. Supervisor P1 P2 P3 P4 Memory Processor 2 Processor 1 Processor 1 working on process 1Processor 2 working on process 4 www.eITnotes.com

11. HOMOGENEOUS PROCESSOR SCHEDULING  The master/slave scheduling technique, besides being conceptually undemocratic, has several performance and operational disadvantages. Under heavy scheduling loads, the master processor may become overloaded and cause a major bottleneck.  A more democratic approach is to treat all processors equally, both master and slave is called homogeneous processor scheduling  Under such conditions, the processor scheduling is logically decentralized. A list of processes and their status are stored so as allow any processor to have access to the list e.q., a common shared area of memory is used.  Whenever a process is stopped due to I/O wait or time limit, etc.. Its processor goes to the process state list and update the process status and finds another process to run. www.eITnotes.com

12.  Each processor uses the same scheduling algorithm to select the process to run the next.  If all processors are handled identically, no policy differences need exist with regard to a single processor or a multiprocessor operating system. www.eITnotes.com