CSC 7600 Lecture 21 : OS 1 Spring 2011 HIGH PERFORMANCE COMPUTING: MODELS, METHODS, & MEANS OPERATING SYSTEMS 1 Prof. Thomas Sterling Center for Computation

CSC 7600 Lecture 21 : OS 1 Spring 2011

HIGH PERFORMANCE COMPUTING: MODELS, METHODS, & MEANS

OPERATING SYSTEMS 1

Prof. Thomas Sterling Center for Computation & TechnologyLouisiana State UniversityApril 5th, 2011


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CSC 7600 Lecture 21 : OS 1 Spring 2011 3

Opening Remarks: Where are We??

• The two ends: what we’ve covered so far– From the top down:

• User applications• Parallel programming methods• Algorithms for distributed computing

– From the bottom up:• Enabling device technologies• Micro architectures• Parallel system architectures

– Performance as cross cutting theme

• We’re now at the system center:– The Operating System– It owns the computer– It controls the applications– It facilitates your needs but limits your access– It protects you from others, and they from you


Opening Remarks: Where are We Going

• Next two lectures are on OS– Principles– Linux components– Middleware

• Practical System Usage (next week)– Scheduling– Check pointing– System Administration

• Beyond and Beyond– You need to know what you don’t know– Field of HPC beyond this Introduction course– Future of HPC over the next decade

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Topics

• Introduction• Operating System Structures & Services• Process Management• Threads• Memory Management• Security & Protection• Modern Operating Systems• Command-line Interpreter System• Unix• Linux Introduction• Summary Materials for Test


Topics



Operating System• What is an Operating System?

– A persistent program that controls the execution of application programs

– An interface between applications and hardware

• Primary functionality– Exploits the hardware resources of one or more processors

– Provides a set of services to system users

– Manages secondary memory and I/O devices

• Objectives– Convenience: Makes the computer more convenient to use

– Efficiency: Allows computer system resources to be used in an efficient manner

– Reliability: through protection between jobs

– Ability to evolve: Permit effective development, testing, and introduction of new system functions without interfering with service

Source: William Stallings “Operating Systems: Internals and Design Principles (5 th Edition)”


Layers of Computer System


Resources Managed by the OS

• Processor• Main Memory

– volatile– referred to as “main memory” or “primary storage”

• Also “physical memory” or “core”• I/O modules

– secondary memory devices– communications equipment– terminals

• System bus– communication among processors, memory, and I/O

modules


OS as Resource Manager

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Memory

Computer SystemI/O Devices

OperatingSystem

Software

Programsand Data

Processor Processor

OSPrograms

Data

Storage

I/O Controller

I/O Controller

Printers,keyboards,digital camera,

etc.

I/O Controller


Topics

• Introduction• Operating System Structures & Services• Process Management• Threads• Memory Management• Security &Protection• Modern Operating Systems• Command-line Interpreter System• Unix• Linux Introduction• Summary Materials for Test


Operating System Structure

• Operating system can be examined in various ways :– Disassembling system components & their interconnections– Services provided by different components of an OS– Interfaces that it makes available to users and programmers

• System Components– Process Management– Main-Memory Management– File Management– I/O System Management– Secondary Storage Management– Networking– Protection & Security Systems

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Operating System Components: Overview

• Process Management: Creating and deleting user and system processes, suspending and resuming processes, mechanisms for process communication, process synchronization, & deadlock handling

• Memory Management: managing usage of memory, loading processes into memory, allocation and de-allocation of memory

• File Management: Creating and deleting files, creating and deleting directories, manipulating files and directories, mapping to secondary storage etc.

• I/O System Management: buffering, caching, spooling, general device driver interfaces drivers for specific hardware devices

• Secondary Storage Management: Free space management, storage allocation, disk scheduling

• Networking: Communication drivers, protocols• Protection & Security systems: Controlling access of programs,

processes, or users to the resources defined by the computer system.

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Operating System Services

• Operating system provides an environment to execute programs. Following are some of the services an Operating System provides :

• Program execution: ability to load a program into memory and execute the program. Program must be able to end execution normally or abnormally.

• I/O operations: help in input/output operations to a file or an I/O device.

• File System Manipulation: read, write, modify, create, delete files by name.

• Communication: facilitate exchange of information between processes through shared memory or message passing.

• Error detection and handling: Monitor for potential errors in CPU, memory hardware, I/O devices, external devices, potential errors in user programs such as access to illegal memory location etc.

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Multiprogramming & Multitasking• Multiprogramming needed for efficiency

– Single user cannot keep CPU and I/O devices busy at all times– Multiprogramming organizes jobs (code and data) so CPU always

has one to execute– A subset of total jobs in system is kept in memory– One job selected and run via job scheduling– When it has to wait (for I/O for example), OS switches to another job

• Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing– Response time should be < 1 second– Each user has at least one program executing in memory process– If several jobs ready to run at the same time CPU scheduling– If processes don’t fit in memory, swapping moves them in and out

to run– Virtual memory allows execution of processes not completely in

memory

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Multiprogramming and Multiprocessing


Topics



Process Management

• A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity.

• Process needs resources to accomplish its task– CPU, memory, I/O, files– Initialization data

• Process is composed of – program counter (points into code section)– process stack (contains temporary data local variables, return

addresses)– code section (executable code)– data section (contains global variables)

• Process termination requires reclaim of any reusable resources• Single-threaded process has one program counter specifying location

of next instruction to execute– Process executes instructions sequentially, one at a time, until

completion• Multi-threaded process has one program counter per thread• Typically system has many processes, some user, some operating

system running concurrently on one or more CPUs– Concurrency by multiplexing the CPUs among the processes /

threads

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Process States

• As a process executes it changes state between one of the following:

• New: A process is being created• Running: Instructions are being executed• Waiting: The process is waiting for some event to occur• Ready: Process is waiting to be assigned to a processor• Terminated: The process has finished execution

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Process Control Block

• Each process in the operating system is represented as a Process Control Block which contains :– Process state: current state of the process (new /

ready / running / waiting / halted…)– Program counter: The address of next instruction to be

executed for the process– CPU registers: Registers vary in number and type

depending on architecture. They include accumulators, index registers, stack pointers, and general purpose registers etc

– CPU scheduling information: process priority, pointers to scheduling queues and other parameters

– Memory Management information: value of base and limit registers, page tables, segment tables etc.

– Accounting information: amount of CPU & real-time used, time limits, job or process numbers

– I/O Status: list of I/O devices allocated to the process, list of open files etc

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Process Management Activities

The operating system is responsible for the following activities in connection with process management:

• Creating and deleting both user and system processes• Suspending and resuming processes• Providing mechanisms for process synchronization• Providing mechanisms for process communication• Providing mechanisms for deadlock handling

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Process Scheduling• When a process enters the system, they are put into a job queue. The queue

consists of all processes in the system.• Processes that are residing in the main memory and are ready and waiting to

execute are kept in a list called the ready queue (usually a linked list)• A ready queue header contains pointers to the first and final PCBs in the list.• List of processes waiting for a particular I/O device is called a device queue. (each

device has its own queue)• A process is initially put into the ready queue where it waits until it is selected for

execution. Once a process is assigned to the CPU for execution one of the following could occur:

– Process could issue an I/O request and be placed in the device queue– Process could create new sub-processes and wait for its termination– Processes could be removed forcibly from the CPU, as a result of an interrupt and could be put

back in the ready queue.

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Process Schedulers

• The OS must select for scheduling purposes, processes from various scheduling queues throughout the lifetime of a process. The selection process is carried out by the appropriate scheduler.

• Often more processes are submitted than can be executed immediately, these processes are spooled to a mass storage device.

• The long-term scheduler or job-scheduler selects processes from this pool and loads them into memory for execution.

• The short-term scheduler selects from among the processes that are ready to execute and allocates CPU to one of them.

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Process Scheduling• In general, a process can be described as I/O bound or CPU bound. • I/O bound process spends more time doing I/O than doing

computations• CPU bound process generates I/O requests infrequently and spends

more time doing computation. • Long term scheduler must schedule a good process mix of I/O bound

& CPU-bound processes. • Some operating systems, may introduce an additional, intermediate

level of scheduling: medium-term scheduler which remove process from memory and reintroduce it into memory at some later time and its execution can be continued where it left off. This scheme is called swapping

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Processes: Context Switch

• Switching the CPU to another process requires saving the state of the old process and loading the saved state of the new process, this task is called Context Switch.

• The context of a process is represented in the PCB of a process; it includes value of CPU registers, process state and memory management information.

• When a context switch occurs, the kernel saves the context of the old process in its PCB and loads the saved context of the new process scheduled to run.

• Context switching time is pure overhead, because the system does no useful work while switching.

• Context switching time is dependent on various factors including; memory speed, number of registers, existence of special instructions, type of machine.

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Topics



Threads

• Threads are sometimes called lightweight processes (LWP), are a basic unit of CPU utilization

• It comprises a threadID, a program counter, a register set, and a stack. A process may have one or more threads of control.

• User threads are supported above the kernel and implemented by a thread library at the user level. – The library provides support for thread creation, scheduling, and

management with no support from the kernel. – Therefore user threads are generally fast to create and manage– Eg: C-threads, UI-threads

• Kernel threads are supported directly by the operating system– Performs thread creation, scheduling, management in kernel space. – Kernel threads are generally slower to create and manage due to

management overhead of the operating system – Eg: Pthreads

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Multi-threading models

• Many systems provide support for both kernel and user threads resulting in multithreading models. Three common types of threading implementations are :

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CPU Scheduling

• The objective of multiprogramming is to have some process running at all time, in order to maximize CPU utilization.

• Scheduling is a fundamental operating system function; almost all resources are scheduled before use. CPU being the primary resource; CPU scheduling has significant impact on OS design & operation

• CPU-I/O Burst Cycle: – Process execution consists of a cycle of CPU

execution and I/O wait; processes alternate between these two states

– Process execution begins with a CPU burst; followed by an I/O burst followed by another CPU burst and then another I/O burst and so on

– The last CPU burst ends with a system request to terminate execution

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Topics



Memory Management

• Memory management determines what is in memory and when– All needed (accessed) data in memory– All needed (executed) instructions in memory in order to

execute– Address translation tables– Optimizing CPU utilization and computer response to users

• Memory management activities– Keeping track of which parts of memory are currently

being used and by whom– Deciding which processes (or parts thereof) and data to

move into and out of memory– Allocating and deallocating memory space as needed– Virtual to physical address translation

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Virtual Memory

• Virtual Memory :– Allows programmers to address memory from a logical point of

view– No hiatus between the execution of successive processes

while one process was written out to secondary store and the successor process was read in

• Virtual Memory & File System :– Implements long-term store– Information stored in named objects called files

• Paging : – Allows process to be comprised of a number of fixed-size

blocks, called pages– Virtual address is a page number and an offset within the page– Each page may be located any where in main memory– Page translation table in memory


Translation Lookaside Buffer


Paging Diagram

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Storage Management• OS provides uniform, logical view of information storage

– Abstracts physical properties to logical storage unit - file– Each medium is controlled by device (i.e., disk drive, tape

drive)• Varying properties include access speed, capacity, data-transfer

rate, access method (sequential or random)

• File-System management– Files usually organized into directories– Access control on most systems to determine who can

access what– OS activities include

• Creating and deleting files and directories• Primitives to manipulate files and directories• Mapping files onto secondary storage• Backup files onto stable (non-volatile) storage media

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Scheduling and Resource Management

• Fairness– Give equal and fair access to resources

• Differential responsiveness– Discriminate among different classes of jobs

• Efficiency– Maximize throughput, minimize response time,

and accommodate as many uses as possible


Topics



Protection and Security

• Protection – any mechanism for controlling access of processes or users to resources defined by the OS

• Security – defense of the system against internal and external attacks– Huge range, including denial-of-service, worms, viruses,

identity theft, theft of service• Systems generally first distinguish among users, to

determine who can do what– User identities (user IDs, security IDs) include name and

associated number, one per user– User ID then associated with all files, processes of that user to

determine access control– Group identifier (group ID) allows set of users to be defined

and controls managed, then also associated with each process, file

– Privilege escalation allows user to change to effective ID with more rights

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OS Kernel• Kernel:

– Portion of operating system that is in main memory

– Contains most frequently used functions

– Also called the “nucleus”, “supervisor”, “monitor”

• Hardware Features:– Memory protection: Do not allow the memory area containing the kernel to be altered

– Timer: Prevents a job from monopolizing the system

– Privileged instructions: Certain machine level instructions can only be executed by the kernel

– Interrupts: Early computer models did not have this capability

• Memory Protection– User program executes in user mode

• Certain instructions may not be executed

– Kernel executes in system mode• Kernel mode• Privileged instructions are executed• Protected areas of memory may be accessed


Topics



Modern Operating Systems

• Small operating system core• Contains only essential core operating systems

functions• Many services traditionally included in the operating

system are now external subsystems– Device drivers– File systems– Virtual memory manager– Windowing system– Security services

• Microkernel architecture– Assigns only a few essential functions to the kernel

• Address spaces/basic memory management

• Interprocess communication (IPC)

• Basic scheduling


Modern Operating Systems

• Multithreading– Process is divided into threads that can run concurrently

• Thread– Dispatchable unit of work– executes sequentially and is interruptable

• Process is a collection of one or more threads

• Symmetric multiprocessing (SMP)– There are multiple processors– These processors share same main memory and I/O facilities– All processors can perform the same functions

• Distributed operating systems– Provides the illusion of a single main memory space and single secondary

memory space

• Object-oriented design– Used for adding modular extensions to a small kernel– Enables programmers to customize an operating system without disrupting

system integrity


Thread and SMP Management

43Example: Solaris Multithreaded Architecture


Benefits of a Microkernel Organization• Uniform interface on request made by a process

– Don’t distinguish between kernel-level and user-level services– All services are provided by means of message passing

• Extensibility– Allows the addition of new services

• Flexibility– New features added & existing features can be subtracted

• Portability– Changes needed to port the system affect only the microkernel itself

• Reliability– Modular design

– Small microkernel can be rigorously tested

• Distributed system support– Message are sent without knowing what the target machine is

• Object-oriented operating system– Uses components with clearly defined interfaces (objects)


Monolithic OS vs. Microkernel

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Topics



Command – Interpreter System

• Command interpreter: is the interface between the user and the operating system

• Some operating systems include the command interpreter in the kernel while others such as MSDOS and UNIX treat command interpreter as a special program

• Commands are given to the operating system by a control statement issued by a user (eg: ls, rm, mv).

• These control statements are interpreted by a command interpreter often known as the shell; whose main function is to get the next command statement and execute it

• Some operating systems offer graphical interfaces (GUIs) to perform the same operations (Windows Interface, Gnome/KDE in Linux)

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• Demonstrate common commands used to interact with the system– Linux

– Windows

We won‘t do this today

DEMO

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Topics



Brief History of UNIX

• Initially developed at Bell Labs in late 1960s by a group including Ken Thompson, Dennis Ritchie and Douglas McIlroy

• Originally named Unics in contrast to Multics, a novel experimental OS at the time

• The first deployment platform was PDP-7 in 1970

• Rewritten in C in 1973 to enable portability to other machines (most notably PDP-11) – an unusual strategy as most OS’s were written in assembly language

• Version 6 (version numbers were determined by editions of system manuals), released in 1976, was the first widely available version outside Bell Labs

• Version 7 (1978) is the ancestor of most modern UNIX systems

• The most important non-AT&T implementation is UNIX BSD, developed at the UC at Berkeley and to run on PDP and VAX

• By 1982 Bell Labs combined various UNIX variants into a single system, marketed as UNIX System III, which later evolved into System V

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Traditional UNIX Organization

• Hardware is surrounded by the operating system software

• Operating system is called the system kernel• Comes with a number of user services and

interfaces– Shell– Components of the C compiler


UNIX Kernel Structure

Source: Maurice J. Bach “The Design of the UNIX Operating System”


UNIX Process Management• Nine process states (see the next slide)

– Two Running states (kernel and user)– Process running in kernel mode cannot be preempted (hence no real-time

processing support)

• Process description– User-level context: basic elements of user’s program, generated directly

from compiled object file– Register context: process status information, stored when process is not

running– System-level context: remaining information, contains static and dynamic

part

• Process control– New processes are created via fork() system call, in which kernel:

• Allocates a slot in the process table,

• Assigns a unique ID to the new process,

• Obtains a copy of the parent process image,

• Increment counters for files owned by the parent,

• Changes state of the new process to Ready to Run,

• Returns new process ID to the parent process, and 0 to the child

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Description of Process States

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Process State Transition Diagram

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UNIX Process

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UNIX Concurrency Mechanisms

• Pipes– Circular buffers allowing two processes to communicate using

producer-consumer model

• Messages– Rely on msgsnd and msgrcv primitives– Each process has a message queue acting as a mailbox

• Shared memory– Fastest communication method– Block of shared memory may be accessed by multiple

processes

• Semaphores– Synchronize processes’ access to resources

• Signals– Inform of the occurrences of asynchronous events

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Traditional UNIX Scheduling

• Multilevel feedback using round-robin within each of the priority queues

• One-second preemption• Priority calculation given by (recomputed once per second):

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Page Replacement Strategy

SVR4 “two-handed clock” policy:• Each swappable page has a reference

bit in page table entry• The bit is cleared when the page is

first brought in• The bit is set when the page is

referenced• The fronthand sets the reference bits

to zero as it sweeps through the list of pages

• Sometime later, the backhand checks reference bits; if a bit is zero, the page is added to page-out candidate list

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UNIX I/O

I/O classes in UNIX:• Buffered (data pass through system

buffers)– System buffer caches

• Managed using three lists: free list, device list and driver I/O queue

• Follows readers/writers model

• Serve block-oriented devices (disks, tapes)

– Character queues• Serve character-oriented devices

(terminals, printers, …)

• Use producer-consumer model

• Unbuffered (typically involving DMA between the I/O module and process I/O area)

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UNIX File Types• Regular

– Contains arbitrary data stored in zero or more data blocks– Treated as stream of bytes by the system

• Directory– Contains list of file names along with pointers to associated nodes (index nodes,

or inodes)– Organized in hierarchies

• Special– Contains no data, but serves as a mapping to physical devices– Each I/O device is associated with a special file

• Named pipe– Implement inter-process communication facility in file system name space

• Link– Provides name aliasing mechanism for files

• Symbolic link– Data file containing the name of file it is linked to

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Directory Structure and File Layout

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Modern UNIX Systems

• System V Release 4 (SVR4)– Developed jointly by AT&T and Sun Microsystems– Improved, feature-rich and most widespread rewrite of System V

• Solaris 10– Developed by Sun Microsystems, based on SVR4

• 4.4BSD– Released by Berkeley Software Distribution– Used as a basis of a number of commercial UNIX products (e.g.

Mac OS X)

• Linux– Discussed in detail later


Modern UNIX Kernel

Source: U. Vahalia “UNIX Internals: The New Frontiers”


Topics

• Introduction• Operating System Structures &Services• Process Management• Threads• Memory Management• Security &Protection• Modern Operating Systems• Command-line Interpreter System• Unix• Linux Introduction• Summary Materials for Test


Linux History

• Initial version written by Linus Torvalds (Finland) in 1991• Originally intended as a non-commercial replacement for the

Minix kernel• Since then, a number of contributors continued to improve Linux

collaborating over the Internet under Torvalds’ control:– Added many features available in commercial counterparts

– Optimized the performance

– Ported to other hardware architectures (Intel x86 and IA-64, IBM Power, MIPS, SPARC, ARM and others)

• The source code is available and free (protected by the GNU Public License)

• The current kernel version is 2.6.29• Today Linux can be found on plethora of computing platforms,

from embedded microcontrollers and handhelds, through desktops and workstations, to servers and supercomputers

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Linux Design

• Monolithic OS– All functionality stored mainly in a single block of code

– All components of the kernel have access to all internal data structures and routines

– Changes require relinking and frequently a reboot

• Modular architecture– Extensions of kernel functionality (modules) can be loaded and

unloaded at runtime (dynamic linking)

– Can be arranged hierarchically (stackable)

– Overcomes use and development difficulties associated with monolithic structure

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Principal Kernel Components

• Signals• System calls• Processes and scheduler• Virtual memory• File systems• Network protocols• Character device drivers• Block device drivers• Network device drivers• Traps and faults• Physical memory• Interrupts

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Topics

• Introduction• Operating System Structures &Services• Process Management• Threads• Memory Management• Security &Protection• Modern Operating Systems• Command-line Interpreter System• Unix• Linux Introduction• Summary Materials for Test


Summary – Material for the Test

• OS introduction 7,8,9,10

• OS structure, services 12,13,14

• Multitasking, Multiprogramming 15,16

• Process Management 18 – 25

• Threads 27 – 29

• Memory Management 31, 32

• Modern OS 41 – 45

• UNIX 51 – 62, 64

• Linux 67


References

• A. Silberschatz, P. Galvin, G. Gagne "Operating System Concepts (6th edition)"

• W. Stallings "Operating Systems: Internals and Design Principles (5th Edition)"

• Maurice Bach "The Design of the UNIX Operating System" • Stallings "official" slides based on the book (one pdf per chapter; most

useful are sections of chapters 2, 3, 4, 7, 8, 9 and 12):– ftp://ftp.prenhall.com/pub/esm/computer_science.s-041/stallings/Slides/

OS5e-PPT-Slides/• Stallings shortened notes on UNIX

– http://www.box.net/public/tjoikg2scz• and Linux:

– http://www.box.net/public/xg654evf8u• J. Moreira et al. paper on BG/L OS design:

– http://sc06.supercomputing.org/schedule/pdf/pap178.pdf


Documents

CSC 7600 Lecture 21 : OS 1 Spring 2011 HIGH PERFORMANCE COMPUTING: MODELS, METHODS, & MEANS OPERATING SYSTEMS 1 Prof. Thomas Sterling Center for Computation