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Operating Systems: Virtualization, Concurrency & Persistence

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Introduction

A Dialogue on the Course

Introduction to Operating Systems

Virtualizing The CPU

Virtualizing Memory

Virtualization: Processes

A Dialogue on Virtualization Introduction to Processes The Abstraction: A Process Process API Process Creation: A Little More Detail Processes States Data Structures Summary Simulator Exercise Quiz on Processes

Virtualization: Process API

Introduction to Process API The fork() System Call The wait() System Call Finally, The exec() System Call Why? Motivating the API Process Control and Users Useful Tools Summary Exercise Quiz on Process API

Virtualization: Direct Execution

Introduction to Direct Execution Basic Technique: Limited Direct Execution Problem #1: Restricted Operations Problem #2: Switching Between Processes Worried About Concurrency?Summary Exercise Quiz on Direct Execution

Virtualization: CPU Scheduling

Introduction to CPU Scheduling Workload Assumptions and Scheduling Metrics First In, First Out (FIFO)Shortest Job First (SJF)Shortest Time-to-Completion First (STCF)A New Metric: Response Time Round Robin Incorporating I/O Summary Simulator Exercise Quiz on CPU Scheduling

Virtualization: Multi-Level Feedback

Introduction to Multi-Level Feedback MLFQ: Basic Rules Attempt #1: How To Change Priority Attempt #2: The Priority Boost Attempt #3: Better Accounting Tuning MLFQ And Other Issues Summary Simulator Exercise Quiz on Multi-level Feedback

Virtualization: Lottery Scheduling

Introduction to Lottery Scheduling Basic Concept: Tickets Represent Your Share Ticket Mechanisms Implementation An Example Why Not Deterministic?The Linux Completely Fair Scheduler (CFS)Weighting (Niceness)How is CFS efficient?Summary Simulator Exercise Quiz on Lottery Scheduling

Virtualization: Multi-CPU Scheduling

Introduction to Multi-CPU Scheduling Background: Multiprocessor Architecture Don’t Forget Synchronization One Final Issue: Cache Affinity Single-Queue Scheduling Multi-Queue Scheduling Linux Multiprocessor Schedulers Summary Simulator Exercise Quiz on Multi-CPU Scheduling Summary Dialogue on CPU Virtualization

Virtualization: Address Space

A Dialogue on Memory Virtualization Early Systems Multiprogramming and Time Sharing The Address Space Goals Summary Exercise Quiz on Address Space

Virtualization: Memory API

Introduction to Memory API Types of Memory The malloc() Call The free() Call Common Errors Underlying OS Support Other Calls Summary Exercise Quiz on Memory API

Virtualization: Address Translation

Introduction to Address Translation Assumptions An Example Dynamic (Hardware-based) Relocation Hardware Support: A Summary Operating System Issues Summary Simulator Exercise Quiz on Address Translation

Virtualization: Segmentation

Introduction to Segmentation Segmentation: Generalized Base/Bounds Which Segment Are We Referring To?What About The Stack?Support for Sharing Fine-Grained vs. Coarse-Grained Segmentation OS Support Summary Simulator Exercise Quiz on Segmentation

Virtualization: Free Space Management

Introduction to Free Space Management Assumptions Low-level Mechanisms Basic Strategies Other Approaches Summary Simulator Exercise Quiz on Free Space Management

Virtualization: Introduction to Paging

Introduction to Paging A Simple Example And Overview Where Are Page Tables Stored?What’s Actually In The Page Table?Paging: Also Too Slow A Memory Trace Summary Simulator Exercise Quiz on Introduction to Paging

Virtualization: Translation Lookaside Buffers

Introduction to Translation Lookaside Buffers TLB Basic Algorithm Example: Accessing An Array Who Handles The TLB Miss?TLB Contents: What’s In There?TLB Issue: Context Switches Issue: Replacement Policy A Real TLB Entry Summary Exercise Quiz on Translation Lookaside Buffer

Virtualization: Advanced Page Tables

Introduction to Advanced Page Tables Simple Solution: Bigger Pages Hybrid Approach: Paging and Segments Multi-level Page Tables Inverted Page Tables Swapping the Page Tables to Disk Summary Simulator Exercise Quiz on Advanced Page Tables

Virtualization: Swapping: Mechanisms

Introduction to Swapping: Mechanisms Swap Space The Present Bit The Page Fault What If Memory Is Full?Page Fault Control Flow When Replacements Really Occur Summary Instructions for Exercise Exercise Quiz on Swapping: Mechanisms

Virtualization: Swapping: Policies

Introduction to Swapping: Policies Cache Management The Optimal Replacement Policy A Simple Policy: FIFO Another Simple Policy: Random Using History: LRU Workload Examples Implementing Historical Algorithms Approximating LRU Considering Dirty Pages Other VM Policies Thrashing Summary Simulator Exercise Quiz on Swapping: Policies

Virtualization: Complete VM Systems

Introduction to Complete VM Systems VAX/VMS Virtual Memory: Memory Management Hardware VAX/VMS Virtual Memory: A Real Address Space VAX/VMS Virtual Memory: Page Replacement VAX/VMS Virtual Memory: Other Neat Tricks The Linux Virtual Memory System: The Linux Address Space The Linux Virtual Memory System: Page Table Structure The Linux Virtual Memory System: Large Page Support The Linux Virtual Memory System: The Page Cache The Linux Virtual Memory System: Security And Buffer Overflows The Linux Virtual Memory System: Other Security Problems Summary Quiz on Complete VM Systems Summary Dialogue on Memory Virtualization

Concurrency: Concurrency and Threads

A Dialogue on Concurrency

Introduction to Concurrency and Threads

Why Use Threads?

An Example: Thread Creation

Why It Gets Worse: Shared Data

The Heart Of The Problem: Uncontrolled Scheduling

The Wish For Atomicity

One More Problem: Waiting For Another

Summary: Why in OS Class?

Quiz on Concurrency and Threads

Concurrency: Thread API

Introduction to Thread API Thread Creation Thread Completion Locks Condition Variables Compiling and Running Summary Simulator Exercise Quiz on Thread API

Concurrency: Locks

Introduction to Locks Locks: The Basic Idea Pthread Locks Building a Lock Evaluating Locks Controlling Interrupts A Failed Attempt: Just Using Loads/Stores Building Working Spin Locks with Test-And-Set Evaluating Spin Locks Compare-And-Swap Load-Linked and Store-Conditional Fetch-And-Add Too Much Spinning: What Now?A Simple Approach: Just Yield, Baby Using Queues: Sleeping Instead of Spinning Different OS, Different Support Two-Phase Locks Summary Exercise Quiz on Locks

Concurrency: Locked Data Structures

Introduction to Locked Data Structures Concurrent Counters Concurrent Linked Lists Concurrent Queues Concurrent Hash Table Summary Exercise Quiz on Locked Data Structures

Concurrency: Conditional Variables

Introduction to Conditional Variables Definition and Routines The Producer/Consumer (Bounded Buffer) Problem Better, But Still Broken: While, Not If The Single Buffer Producer/Consumer Solution Covering Conditions Summary Instructions For Exercise Exercise Quiz on Condition Variables

Concurrency: Semaphores

Introduction to Semaphore Semaphores: A Definition Binary Semaphores (Locks)Semaphores for Ordering The Producer/Consumer (Bounded Buffer) Problem Extending The Solution for Multiple Producers And Consumers Reader-Writer Locks The Dining Philosophers Thread Throttling How to Implement Semaphores Summary Exercise Quiz on Semaphores

Concurrency: Concurrency Bugs

Introduction to Concurrency Bugs What Types of Bugs Exist?Non-Deadlock Bugs Deadlock Bugs Prevention Deadlock Avoidance via Scheduling Detection And Recovery Summary Instructions for Exercise Exercise Quiz on Concurrency Bugs

Concurrency: Event-Based Concurrency

Introduction to Event-Based Concurrency The Basic Idea: An Event Loop An Important API: select() or poll()Using select()A Problem: Blocking System Calls A Solution: Asynchronous I/O Another Problem: State Management What Is Still Difficult With Events Summary Exercise Quiz on Event-based Concurrency Summary Dialogue on Concurrency

Persistence: I/O Devices

A Dialogue on Persistence Introduction to I/O Devices System Architecture A Canonical Device The Canonical Protocol Lowering CPU Overhead with Interrupts More Efficient Data Movement with DMA Methods of Device Interaction Fitting into the OS: The Device Driver Case Study: A Simple IDE Disk Driver Historical Notes Summary Quiz on I/O Devices

Persistence: Hard Disk Drives

Introduction to Hard Disk Drives The Interface Basic Geometry A Simple Disk Drive A Disk Drive with Multiple Tracks: Seek Time More Details About Hard Drives I/O Time: Doing the Math Disk Scheduling Some Other Scheduling Issues Summary Simulator Exercise Quiz on Hard Disk Drives

Persistence: Redundant Disk Arrays (RAID)

Introduction to RAID Interface and RAID Internals Fault Model How to Evaluate a RAID RAID Level 0: Striping RAID Level 1: Mirroring RAID Level 4: Saving Space With Parity RAID Level 5: Rotating Parity RAID Comparison: A Summary Other Interesting RAID Issues Summary Simulator Exercise Quiz on Redundant Disk Arrays (RAID)

Persistence: Files and Directories

Introduction to Files and Directories Files and Directories The File System Interface Reading and Writing Files Reading and Writing, but not Sequentially Shared File Table Entries: fork() and dup()Writing Immediately With fsync()Renaming Files Getting Information About Files Removing Files Making Directories Reading and Deleting Directories Hard Links Symbolic Links Permission Bits and Access Control Lists Making and Mounting a File System Summary Exercise Quiz on Files and Directories

Persistence: File System Implementation

Introduction to File System Implementation The Way to Think Overall Organization File Organization: The Inode Directory Organization Free Space Management Access Paths: Reading and Writing Caching and Buffering Summary Simulator Exercise Quiz on File System Implementation

Persistence: Fast File System

Introduction to Fast File System The Problem: Poor Performance FFS: Disk Awareness Is The Solution Policies: How to Allocate Files and Directories Measuring File Locality The Large-File Exception A Few Other Things About FFS Summary Simulator Exercise Quiz on Fast File System

Persistence: FSCK and Journaling

Introduction to FSCK and Journaling

A Detailed Example

Solution #1: The File System Checker

Solution #2: Journaling (or Write-Ahead Logging)

Metadata Journaling

Solution #3: Other Approaches

Quiz on FSCK and Journaling

Persistence: Log-Structured File System

Introduction to Log-Structured File System Writing to Disk Sequentially Writing Sequentially and Effectively How Much to Buffer?Problem: Finding Inodes Solution Through Indirection: The Inode Map Completing the Solution: The Checkpoint Region Reading a File from Disk: A Recap What About Directories?A New Problem: Garbage Collection Determining Block Liveness A Policy Question: Which Blocks to Clean, and When?Crash Recovery and the Log Summary Simulator Exercise Quiz on Log-Structured File System

Persistence: Flash-based SSDs

Introduction to Flash-based SSDs Storing a Single Bit From Bits to Banks/Planes Basic Flash Operations Flash Performance and Reliability From Raw Flash to Flash-Based SSDs FTL Organization: A Bad Approach A Log-Structured FTL Garbage Collection Mapping Table Size Wear Leveling SSD Performance and Cost Summary Simulator Exercise Quiz on Flash-based SSDs

Persistence: Data Integrity and Protection

Introduction to Data Integrity and Protection Disk Failure Modes Handling Latent Sector Errors Detecting Corruption: The Checksum Using Checksums A New Problem: Misdirected Writes One Last Problem: Lost Writes Scrubbing Overheads of Checksumming Summary Simulator Exercise Quiz on Data Integrity and Protection Summary Dialogue on Persistence

Distribution: Distributed Systems

A Dialogue on Distribution Introduction to Distributed Systems Communication Basics Unreliable Communication Layers Reliable Communication Layers Communication Abstractions Remote Procedure Call (RPC)Summary Exercise Quiz on Distributed Systems

Distribution: Network File System (NFS)

Introduction to Network File System (NFS)A Basic Distributed File System On to NFS Key to Fast Crash Recovery: Statelessness The NFSv2 Protocol From Protocol to Distributed File System Handling Server Failure with Idempotent Operations Improving Performance: Client-side Caching The Cache Consistency Problem Implications on Server-Side Write Buffering Summary Instructions For Exercise Exercise Quiz on Network File System (NFS)

Distribution: Andrew File System (AFS)

Introduction to Andrew File System (AFS)AFS Version 1 Problems with Version 1 AFS Version 2 Cache Consistency Crash Recovery Scale and Performance of AFSv2 AFS: Other Improvements Summary Simulator Exercise Quiz on Andrew File System (AFS)Summary Dialogue on Distribution

Simulator

This lesson explains how to interact with the simulator for the exercise presented in the next lesson.

This exercise introduces fsck.py, a simple file system simulator. Some familiarity with the vsfs.py simulator (described in an earlier chapter on file system implementation would be useful, but is not necessary.

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