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Nachos Assignment#2

Nachos Assignment#2. Priority Scheduling. Nachos scheduling policy :FIFO. Jobs run to completion in order of arrival. In interactive systems, run until I/O; after I/O completes, put back at end of queue . Response time poor . Scheduling is handled by routines in the Scheduler object:.

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Nachos Assignment#2

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  1. Nachos Assignment#2 Priority Scheduling

  2. Nachos scheduling policy :FIFO • Jobs run to completion in order of arrival. • In interactive systems, run until I/O; after I/O completes, put back at end of queue . • Response time poor . • Scheduling is handled by routines in the Scheduler object:

  3. Scheduler • The scheduler is invoked whenever the current thread wishes to give up the CPU • For example, the current thread may have initiated an I/O operation and must wait for it to complete before executing further

  4. Implement priority scheduling • Add the method void Thread:SetPriority (int p) to set the priority of a thread. • When the scheduler makes a decision as to next thread to run from the readyList,it selects the thread with the highest priority. • The higher the value of p, the higher the priority.

  5. Thread introduction • Status: • READY: • RUNNING: • BLOCKED: • JUST_CREATED:

  6. Thread introduction • Some operations: • Fork(VoidFunctionPtr func, int arg) • Initialize the stack and put the thread on the ready queue • void Yield() • Suspend the calling thread and select a new one for execution

  7. Class “thread” • Add member data “priority” • Add member function • getPriority • setPriority

  8. Class “list” • Original: • void Prepend(T item); • void Append(T item); • Add following method (e.g.): • Void SortedPrepend(); • Void SortedAppend();

  9. void ReadyToRun(Thread *thread): • Make thread ready to run and place it on the ready list • It simply changes its state to READY and places it on the ready list • ReadyToRun is invoked, for example, by Thread::Fork() after a new thread has been created. • Modify: readyList->Append(thread);

  10. Thread *FindNextToRun(): • Select a ready thread and return it. • FindNextToRun simply returns the thread at the front of the ready list. • Modify: return readyList->RemoveFront() //If priority of selected thread is lower,put it back and return NULL

  11. void Run(Thread *nextThread): • Do the dirty work of suspending the current thread and switching to the new one. • Note that it is the currently running thread that calls Run(). A thread calls this routine when it no longer wishes to execute. • Change the state of newly selected thread to RUNNING

  12. Project grading policy • Primary requirement • Priority scheduling implementation :85% • Documentation :15% • Bonus • How to verify your work?: +20%

  13. Project Deadline • 6/25 24:00 • E-mail your project to r91050@im.ntu.edu.tw • Use student id as file name.(one of the two group member) Ex:R91725050

  14. Your files SHOULD include: • Modified files • Test files (Bonus) • 5 page-report • Do not put source code in your report. • Explain why you chose to modify these files. • Problems encountered and your solution • Anything else. • Package your files in .tar or .zip format.

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