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% This file is a template using the "beamer" package to create slides for a talk or presentation
% - Talk at a conference/colloquium.
% - Talk length is about 20min.
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% MODIFIED by Jonathan Kew, 2008-07-06
% The header comments and encoding in this file were modified for inclusion with TeXworks.
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\documentclass{beamer}


% Copyright 2004 by Till Tantau <tantau@users.sourceforge.net>.
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% In principle, this file can be redistributed and/or modified under
% the terms of the GNU Public License, version 2.
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% package/program, I grant the extra permission to freely copy and
% modify this file as you see fit and even to delete this copyright
% notice. 


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\title[IOSY 332C \& IOPS 332C: OS] % (optional, use only with long paper titles)
{ Lecture  5- CPU Scheduling}

%\subtitle
%{Include Only If Paper Has a Subtitle}

\author [Bibhas Ghoshal]% (optional, use only with lots of authors)
{ Instructor : Bibhas Ghoshal (\textcolor{black}{bibhas.ghoshal@iiita.ac.in})} 



% - Give the names in the same order as the appear in the paper.
% - Use the \inst{?} command only if the authors have different
%   affiliation.

%\institute % (optional, but mostly needed)
%{
  %\inst{1}%
 % Department of Computer Science and Engineering\\
 % Indian Institute of Technology, Kharagpur}

%  \and
 % \inst{2}%
  %Department of Theoretical Philosophy\\
  %University of Elsewhere}
% - Use the \inst command only if there are several affiliations.
% - Keep it simple, no one is interested in your street address.

\date% (optional, should be abbreviation of conference name)
{Autumn Semester, 2015}
% - Either use conference name or its abbreviation.
% - Not really informative to the audience, more for people (including
%   yourself) who are reading the slides online

%\subject{Theoretical Computer Science}
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% out. 



% If you have a file called "university-logo-filename.xxx", where xxx
% is a graphic format that can be processed by latex or pdflatex,
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\pgfdeclareimage[height=0.75cm]{university-logo}{IIIT_logo.jpg}
 \logo{\pgfuseimage{university-logo}}



% Delete this, if you do not want the table of contents to pop up at
% the beginning of each subsection:
% \AtBeginSubsection[]
% {
%   \begin{frame}<beamer>{Outline}
%     \tableofcontents[currentsection,currentsubsection]
%   \end{frame}
% }


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%\beamerdefaultoverlayspecification{<+->}


\begin{document}

\begin{frame}
  \titlepage
\end{frame}

\begin{frame}{Lecture Outline}
  \begin{itemize}
   \item CPU Scheduling Basics
   \item CPU Scheduler and Dispatcher
   \item Scheduling Criteria
   \item First Come First Serve (FCFS) Scheduling
   \item First Shortest Job First (SJF) Scheduling
 \end{itemize}
        
        
\textcolor{black}{References and Illustrations have been used from:}
 \begin{itemize}
  \item lecture slides of the book - Operating System Concepts by Silberschatz, Galvin and Gagne, 2005 
  \item Modern Operating System by Andrew S. Tanenbaum
  \item lecture slides of CSE 30341: Operating Systems (Instructor : Surendar Chandra), 
 \end{itemize}

  
\end{frame}



 \begin{frame}{CPU Scheduling: Basic Concepts}



 \begin{itemize}
  \item Maximum CPU utilization obtained with multiprogramming - several processes are kept in memory, while one is waiting for I/O, the OS gives the CPU to another process
   \item CPU scheduling depends on the observation that processes cycle between CPU execution and I/O wait.
     \end{itemize}
\end{frame}
\begin{frame}{Alternating Sequence of CPU And I/O Bursts}
 \begin{figure}
  \centering
  \includegraphics[width=0.85\textwidth]{cpu_io.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
 
 \end{frame}
 
 \begin{frame}{Histogram of CPU Burst Times}
 \begin{figure}
  \centering
  \includegraphics[width=0.75\textwidth]{histogram.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
 
 \end{frame}

 

 
 
 
 
 \begin{frame}{CPU Scheduler}
 
 
 
 \begin{itemize}
  \item Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them
  \item CPU scheduling decisions may take place when a process:
     \begin{enumerate}
	\item Switches from running to waiting state (e.g. I/O request)
	 \item Switches from running to ready state (e.g. Interrupt)
	\item Switches from waiting to ready (e.g. I/O completion)
	\item Terminates
    \end{enumerate}	
  \item Scheduling under 1 and 4 is \emph{non-preemptive} (cooperative)
  \item All other scheduling is \emph{preemptive} - have to deal with possibility that operations (system calls) may be incomplete
 \end{itemize}

 
\end{frame}


\begin{frame}{Dispatcher}
 
 \begin{itemize}
  \item Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves:
     \begin{enumerate}
	\item switching context
	 \item switching to user mode
	\item jumping to the proper location in the user program to restart that program
	
    \end{enumerate}	
  \item Dispatch latency – time it takes for the dispatcher to stop one process and start another running
       \begin{itemize}
        \item Should be as low as possible
       \end{itemize}

 \end{itemize}

 
\end{frame}

\begin{frame}{Scheduling Criteria}
\begin{itemize}
\item CPU utilization (max) – keep the CPU as busy as possible
\item Throughput (max) – \# of processes that complete their execution per time unit
\item Turnaround time (min) – amount of time to execute a particular process
\item Waiting time (min) – amount of time a process has been waiting in the ready queue
\item Response time (min) – amount of time it takes from when a request was submitted until the first response is produced, not output  (for time-sharing environment)
\item In typical OS, we optimize each to various degrees depending on what we are optimizing the OS
 
\end{itemize}
 
\end{frame}

\begin{frame}{Optimization Criteria}
\begin{itemize}
 \item Max CPU utilization
\item Max throughput
\item Min turnaround time 
\item Min waiting time 
\item Min response time

\item Analysis using Gantt chart (illustrates when processes complete)
\end{itemize}

\end{frame}

\begin{frame}{First Come First Serve (FCFS)  Scheduling}
\begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{fcfs.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
 
\end{frame}

 \begin{frame}{First Come First Serve Scheduling}
\begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{fcfs1.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
 
\end{frame}


\begin{frame}{Shortest Job First (SJF)}
 \begin{itemize}
  \item Associate with each process the length of its next CPU burst.  Use these lengths to schedule the process with the shortest times
  \item Two schemes: 
     \begin{itemize}
      \item \emph{nonpreemptive} – once CPU given to the process, it cannot be preempted until completes its CPU burst
      \item \emph{preemptive} – if a new process arrives with CPU burst length less than remaining time of current executing process, preempt.  This scheme is know as the \textbf{Shortest-Remaining-Time-First (SRTF)}
     \end{itemize}



\item SJF is optimal – gives minimum average waiting time for a given set of processes
 \end{itemize}

 
\end{frame}

 \begin{frame}{Non-preemptive SJF}
  
  \begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{sjf.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
  
 \end{frame}

 \begin{frame}{Preemptive SJF}
  
  \begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{sjf_premptive.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
  
  
 \end{frame}
 
 \begin{frame}{Determining Length of Next CPU Burst}
 \begin{itemize}
  \item Can only estimate the length
\item Can be done by using the length of previous CPU bursts, using exponential averaging

\begin{enumerate}
 \item $t_{n}$ = actual length of $n^{th}$ CPU burst
 \item $\tau_{n+1}$ = predicted value of next CPU burst
 \item $\alpha$ = $0 \leq \alpha \leq 1$
 \item $\tau_{n+1} = \alpha \tau_{n} + (1-\alpha) \tau_{n}$
\end{enumerate}



 \end{itemize}

  
 \end{frame}

 
 \begin{frame}{Prediction of the Length of the Next CPU Burst}
   \begin{figure}
  \centering
  \includegraphics[width=0.65\textwidth]{next_burst.pdf}
  %\caption{Process created during execution of a.out}
 \end{figure}
 \end{frame}
% 
%  
 \begin{frame}{Examples of Exponential Averaging}
  \begin{itemize}
   \item if $\alpha = 0 \implies \tau_{n+1}  =  \tau_{n} $ : Recent history does not count
   \item if $\alpha = 1 \implies \tau_{n+1} = t_{n}$ : Only the actual last CPU burst counts
  \end{itemize}

  
  
 \end{frame}
%  
%  
%  

\end{document}