FINAL EXAM oerating system, Summaries of Operating Systems

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CHAPTER 6

UNDERSTANDING OPERATING

LECTURE 7:

CONCURRENT PROCESSES

After completing this chapter, you should be able to describe:  The critical difference between processes and processors, and their connection  The differences among common configurations of multiprocessing systems  The significance of a critical region in process synchronization  The basic concepts of process synchronization software: test-and- set, WAIT and SIGNAL, and semaphores 2

Parallel processing  Multiprocessing  Two or more processors operate in unison  Two or more CPUs execute instructions simultaneously  Processor Manager  Coordinates activity of each processor  Synchronizes interaction among CPUs 4 First of all, understand what is a Multiprocessing system, click on https://www.youtube.com/watch?v=IZfWjg3U3mA

 Parallel processing development

 Enhances throughput

 Increases computing power

 *Benefits

 Increased reliability

 More than one CPU

 If one processor fails, others take over

 Not simple to implement

 Faster processing

 Instructions processed in parallel two or more at a time

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 Developed for high-end midrange and mainframe computers  Each additional CPU treated as additional resource  Today hardware costs reduced (Moore’s law)  Multiprocessor systems available on all systems  Multiprocessing occurs at three levels  Job level  Process level  Thread level  Each requires different synchronization frequency Understanding Operating Systems, Sixth Edition (^) 8

 Multi-core processing  Several processors placed on single chip  Problems  Heat and current leakage (tunneling)  Solution  Single chip with two processor cores in same space  Allows two sets of simultaneous calculations  80 or more cores on single chip  Two cores each run more slowly than single core chip Understanding Operating Systems, Sixth Edition (^) 10

 Multiple processor configuration impacts systems  *Three types  Master/slave  Loosely coupled  Symmetric 11 To understand more onTypes of Multiprocessing system, click on https://www.youtube.com/watch?v=So9SR3qpWsM

 Advantages  Simplicity  Disadvantages  Reliability  No higher than single processor system  Potentially poor resources usage  Increases number of interrupts Understanding Operating Systems, Sixth Edition (^) 14

 Decentralized processor scheduling  Each processor is same type  Advantages (over loosely coupled configuration)  More reliable  Uses resources effectively  Can balance loads well  Can degrade gracefully in failure situation  Most difficult to implement  Requires well synchronized processes  Avoids races and deadlocks Understanding Operating Systems, Sixth Edition (^) 17

 Decentralized process scheduling  Single operating system copy  Global table listing  Interrupt processing  Update corresponding process list  Run another process  More conflicts  Several processors access same resource at same time  Process synchronization  Algorithms resolving conflicts between processors Understanding Operating Systems, Sixth Edition (^) 19

 Successful process synchronization  Lock up used resource  Protect from other processes until released  Only when resource is released  Waiting process is allowed to use resource  Mistakes in synchronization can result in:  Starvation  Leave job waiting indefinitely  Deadlock  If key resource is being used Understanding Operating Systems, Sixth Edition (^) 20