Nachos Project Assignment 2System Call & CPU scheduling

TA: Chien-Wen, Huang.

Advisor: Farn, Wang.

2015/11/18

Outline

• Part 1. System Call• Sleep

• Part 2. CPU Scheduling• FCFS

• SJF

• Priority

• Report

• Grading Policy & Late Policy

• Reference

If you still have trouble to install Nachos

• make Error 127?• https://code.google.com/p/damody/downloads/detail?name=mips-

decstation.linux-xgcc.gz

• In fact, I have sent a mail about this problem at Oct.29.

• Make Error: cast from ‘void (*)()’ to ‘int’ lose precision.• Use 32-bits machine!

• Other Problem?

Part 1. System CallSleep

Part 1. System call – Sleep()

• Implement a system call – Sleep()• userprog/syscall.h

• Define a system call number of Sleep

• test/start.s• Prepare registers for Sleep

• userprog/exception.cc• Add a new case for Sleep in ExceptionHandler

• Note the use of kernel->alarm->WaitUntil()

• You can try implement some other kinds of system call.• Might be considered as bonus!

System call:start.s

• Assembly language assist to make system calls to the Nachos kernel

• http://www.mrc.uidaho.edu/mrc/people/jff/digital/MIPSir.html• Take System call PrintInt as an example

.globl PrintInt

.ent PrintInt

PrintInt:

addiu $2,$0,SC_ PrintInt

// put system call number in register 2

syscall

/* all parameter of this system call will be stored in register4, 5, 6, and 7 by MIPS machine automatically. */

.end PrintInt

Part 1. System call – Sleep()

• /code/threads/alarm.h

• /code/threads/alarm.cc

• The WaitUntil() will be called when a thread going to sleep.

• Call the CallBack() to check which thread should wake up.

• See the comments in the file, they are helpful.

• Don’t forget the useful data structure like list in the lib folder.

Part 1. System call – Sleep()

• Q: How to write my own test code like test1 and test2?

• A: Write them in the same way as other test code.

• Take a test code named “test” as an example:• Create test.c in code/test/

• Modify the Makefile in code/test/

• In the same way as test1 and test2

• Type “make” in code/test/

Part 2. CPU SchedulingFCFS, SJF, Priority.

Part 2. CPU Scheduling

• Choose at least ONE of the following to implement:• First-Come-First-Service(FCFS)

• Shortest-Job-First(SJF)

• Priority

• Otherwise

• The extra implementation will be considered as BONUS.

• Design your own test code:• You can find Class::SelfTest() in many classes.

• Implement some test code, and call it in SelfTest().

Example. Non-preemptive shortest job first scheduler• Nachos default scheduler: Round Robin

• Shortest job first

• n+1 = tn + (1- )n

• n time of the nth predicate CPU burst

• tn time of the nth actual CPU burst

Example. Non-preemptive shortest job first scheduler• thread/alarm.cc, thread/alarm.h

• Implement WaitUntil(int x) to handle sleep(int t)

• Add a class to management the threads which are sleeping

Begin Running

Invoke Sleep(x)

Per timer interrupt:1.Record actual CPU burst2.Wake up time up threads

1.Set next predicted CPU burst2.Insert this thread to Sleeping thread lists3.Invoke thread->Sleep

Part 2. CPU Scheduling

• Only FCFS, SJF, priority available?• You can choose any scheduling algorithm from lecture.

• Specify your algorithm in the report.

• Design at least 2 test case to proof your result• Specify the test case setting and plot that screenshot in your report.

• Design the nachos interface to switch different scheduling algorithm if you implement more than one.

Some files that might useful.

• To change the program interface:• threads/main.cc

• To make your own SelfTest() function:• threads/thread.h

• threads/thread.cc

• To call your test code in ThreadedKernel:• threads/kernel.cc

Some files that might useful.

• Recall Part 1.• threads/alarm.h

• threads/alarm.cc

• Where are the schedulers?• threads/scheduler.h

• threads/scheduler.cc

• Useful data structure• E.g. lib/list.h for SortedList.

15

Report & PolicyReport contents, grading policy, late policy and the summary.

Report

• Report• Motivation and the problem analysis.

• What’s your plan to deal with the problem(high-level).

• How you really implement to solve the problem in Nachos.

• You can including some (not all) important code segments and comments.

• Experiment result and some discussion.

• Extra effort (e.g. bonus part) or observation.

• Remember there are two parts in project2.

• Please saved as [Student ID]_NachOS_report.pdf• E.g. r04942044_NachOS_report.pdf

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Bonus

• Implement more than one scheduling algorithm.• Tell me how to switch different scheduling algorithm in your program in the

report or the README.

• You can implement any kind of scheduling algorithm

• Extra observation or modification on nachos.

• Please write down on your report if you did it.

Hand in source code & report

• Source Code

• tar zcvf [Student ID]_Nachos2.tar.gz ./nachos-4.0

• E.g. r04942044_Nachos2.tar.gz

• Mail your source code and report to r04942044@ntu.edu.tw• One pdf file as report and one tar.gz file as source code.

• Deadline: Dec.16.2015, 23:59:59.

19

Grading PolicyWith presentation• Nachos source code: (40%)

• Part 1: (20%)

• Part 2: (20%)

• Report: (30%)

• Correct format: (10%)

• Presentation: (20%)

• Bonus

Grading PolicyWithout presentation• Nachos source code: (50%)

• Part 1: (25%)

• Part 2: (25%)

• Report: (40%)

• Correct format: (10%)

• Bonus

Late Policy

• 10% penalty per day.

• Late penalty only holds for a week• After 7 days, you will get 70% penalty, but no more penalty after that.

• That is, after n(n>=7) days, you will still get 70% penalty.

• Don’t give up!

• No plagiarism.

Summary

• Part 1. System Call

• Part 2. Implement at least one scheduling algorithm in previous slide.

• Write the report.

• Send to TA in the correct format before the deadline.• Dec.16.2015, 23:59:59

• Prepare the presentation if you should.

Reference

• Nachos System Call Implementation Sample.• http://puremonkey2010.blogspot.tw/2013/05/nachos-40-nachos-system-

call.html

• Nachos Beginner’s Guide:• https://www.ida.liu.se/~TDDI12/material/begguide/