Operating System & Memory Hierarchy i206 Fall 2010 John Chuang Some slides adapted from Glenn Brookshear, Brian Hayes, or Marti Hearst

Operating System & Memory Hierarchy

i206 Fall 2010

John Chuang

Some slides adapted from Glenn Brookshear, Brian Hayes, or Marti Hearst

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Summary of Key Concepts

Data Storage:- Bit storage using transistors- Memory hierarchy- Locality of reference and caching

Operating System:- Process management- Context switch- Threads vs. processes- Synchronization and locks

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Memory Hierarchy

Bits & BytesBinary Numbers

Number Systems

Gates

Boolean Logic

Circuits

CPU Machine Instructions

Assembly Instructions

Program Algorithms

Application

Memory

Data compression

Compiler/Interpreter

OperatingSystem

Data Structures

Analysis

I/O

Memory hierarchy

Design

Methodologies/Tools

Process

Truth tableVenn DiagramDeMorgan’s Law

Numbers, text,audio, video, image, …

Decimal, Hexadecimal, Binary

AND, OR, NOT, XOR, NAND, NOR,etc.

Register, CacheMain Memory,Secondary Storage

Context switchProcess vs. ThreadLocks and deadlocks

Op-code, operandsInstruction set arch

Lossless v. lossyInfo entropy & Huffman code Adders, decoders,

Memory latches, ALUs, etc.

DataRepresentation

Data

Data storage

Principles

ALUs, Registers,Program Counter, Instruction Register

Network

Distributed Systems Security

Cryptography

Standards & Protocols

Inter-processCommunication

Searching, sorting,Encryption, etc.

Stacks, queues,maps, trees, graphs, …

Big-O

UML, CRC

TCP/IP, RSA, …

ConfidentialityIntegrityAuthentication…

C/S, P2PCaching

sockets

Formal models

Finite automataregex

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Storing1 Bit ofData

Flip-flop (also called a latch) is a circuit built from gates that can store one bit of data- Setting input A to 1 sets output to 1- Setting input B to 1 sets output to 0- While both input lines are 0, the most recently stored value is preserved

Adapted from Brookshear Fig 1.5

output

Input A

Input B

Example: This 8-bit memory cell can store a byte of data.

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Data Storage

Where and how do we store data?

Brookshear Fig 2.13

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Data Storage

In general, we want data to be located in close proximity of their use (the CPU in this case)

Why do we want to store data at so many different locations within a computer?

Considerations of- Storage capacity- Access latency- Cost- …- Patterns of data access

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Memory Hierarchy

Image from http://www.howstuffworks.com/computer-memory1.htm

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Storage Technologies

Characteristics- Solid State vs.

Mechanical- Volatile vs. Nonvolatile- Read only vs. Read-write

(RW)- Expense- Speed- Storage capacity (a

function of size & expense)

Types:- Registers: Volatile,

small, expensive, fast, solid state, RW

- DRAM (dynamic random access memory): Volatile, now large, expensive, fast, solid state, RW

- ROM (read-only memory): Nonvolatile, Read-only, cheap, fast

- Hard Disk: Nonvolatile, mechanical, RW, cheap, slow

- Flash Memory (aka SSD): Nonvolatile, solid state, RW, expensive, fast (Versus hard disk: silent, lighter, faster … but more expensive)

- Other external storage: CD-ROM, floppy disks, magnetic tape, …

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Levels of a Memory Hierarchy(circa 2000)

http://www.ece.arizona.edu/~ece369/lec10S01/sld047.htm

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Data Storage

In general, we want data to be located in close proximity of their use (the CPU in this case)

Why do we want to store data at so many different locations within a computer?

Considerations of- Storage capacity- Access latency- Cost- …- Patterns of data access

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Caching Data access patterns

exhibit locality of reference- Recently referenced item

more likely to be referenced again

Caches store items that have been used recently for faster access

Caching can be done at various levels of the memory hierarchy

Image from http://cne.gmu.edu/modules/vm/orange/realprog.html

ALU Registers

R

W

R

W

R

W

L1/L2Cache

MainMemory

R

WDisk

Storage

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OperatingSystem

Bits & BytesBinary Numbers

Number Systems

Gates

Boolean Logic

Circuits

CPU Machine Instructions

Assembly Instructions

Program Algorithms

Application

Memory

Data compression

Compiler/Interpreter

OperatingSystem

Data Structures

Analysis

I/O

Memory hierarchy

Design

Methodologies/Tools

Process

Truth tableVenn DiagramDeMorgan’s Law

Numbers, text,audio, video, image, …

Decimal, Hexadecimal, Binary

AND, OR, NOT, XOR, NAND, NOR,etc.

Register, CacheMain Memory,Secondary Storage

Context switchProcess vs. ThreadLocks and deadlocks

Op-code, operandsInstruction set arch

Lossless v. lossyInfo entropy & Huffman code Adders, decoders,

Memory latches, ALUs, etc.

DataRepresentation

Data

Data storage

Principles

ALUs, Registers,Program Counter, Instruction Register

Network

Distributed Systems Security

Cryptography

Standards & Protocols

Inter-processCommunication

Searching, sorting,Encryption, etc.

Stacks, queues,maps, trees, graphs, …

Big-O

UML, CRC

TCP/IP, RSA, …

ConfidentialityIntegrityAuthentication…

C/S, P2PCaching

sockets

Formal models

Finite automataregex

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Abstract View of System Components

Source: Silberschatz, Galvin, Gagne

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What is an Operating System? A software program that acts as an intermediary between a user of a computer and the computer hardware

Operating system functions:- Oversee operation of computer- Store and retrieve files- Schedule programs for execution- Execute programs

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OS Components

Shell (command interpreter) Kernel

- Process manager- Memory manager- File manager- I/O systems manager- Networking- Scheduler/dispatcher- Etc.

shell

user

user

user

kernel

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Process Management

A process is a program in execution- A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task

The operating system is responsible for the following activities in connection with process management- Process creation and deletion- Process suspension and resumption- Provision of mechanisms for:

- process synchronization- process communication

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Process State

As a process executes, it changes state- new: The process is being created.- running: Instructions are being executed.- waiting: The process is waiting for some event

to occur.- ready: The process is waiting to be assigned to

a process.- terminated: The process has finished execution.


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Resource Sharing Many processes share hardware resources

- CPU, I/O (mouse, keyboard, monitor, disk, …) Processes must take turns

- Context switch (aka process switch) Operating system serves as coordinator/ scheduler

Brookshear Fig 3.6

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Context Switch

When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process

Process control block (PCB, on right) contains information associated with each process

Context-switch time is overhead; the system does no useful work while switching- A system is said to be “thrashing” when it spends more time performing context switches than useful work


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Threads A thread (or lightweight process) is a basic unit of CPU utilization

Each thread has its own- program counter- stack- register set

The threads share:- text section (program)

- data section (global variables)


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Threads versus Multiple Processes

Threads are cheaper to create than processes (~10-20x)

Switching to a different thread in same process is much cheaper than switching to a different process (~5-50x) since no context switching required

Threads within same process can share data and other resources more conveniently and efficiently (than Inter-Process Communication)

Threads within a process are not protected from one another

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Synchronization

Scenario: two threads want to update count (current value is 4)- Thread 1: count = count + 1- Thread 2: count = count - 1

What is final value of count?- (a) 3- (b) 4- (c) 5- (d) any of the above- (e) none of the above

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Synchronization

LOAD R1, XY LOAD R2, #1 ADD R3, R1, R2 STORE R3, XY

LOAD R4, XY LOAD R5, #-1 ADD R6, R4, R5 STORE R6, XY

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Synchronization

LOAD R1, XY LOAD R2, #1 ADD R3, R1, R2 STORE R3, XY LOAD R4, XY LOAD R5, #-1 ADD R6, R4, R5 STORE R6, XY

LOAD R1, XY LOAD R4, XY LOAD R2, #1 LOAD R5, #-1 ADD R3, R1, R2 ADD R6, R4, R5 STORE R3, XY STORE R6, XY

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Lesson

Even a seemingly simple operation like count++ is not atomic, and can be subject to race conditions

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Synchronization Use locks to coordinate actions of competing processes

Also known as mutual exclusion (mutex)

Simplest form of lock is a semaphore- Process must acquire semaphore before entering critical section; release semaphore upon exit

initialize_lock() ... acquire_lock() try: change_shared_data() finally: release_lock()

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Summary of Key Concepts

Data Storage:- Bit storage using transistors- Memory hierarchy- Locality of reference and caching

Operating System:- Process management- Context switch- Threads vs. processes- Synchronization and locks

Documents

Operating System & Memory Hierarchy i206 Fall 2010 John Chuang Some slides adapted from Glenn Brookshear, Brian Hayes, or Marti Hearst