Chapter 13: I/O Systems - Radford Universitymhtay/CPSC371/Lecture/ch13.pdf · Chapter 13: I/O...
Transcript of Chapter 13: I/O Systems - Radford Universitymhtay/CPSC371/Lecture/ch13.pdf · Chapter 13: I/O...
Chapter 13: I/O SystemsChapter 13: I/O Systems
13.2 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Chapter 13: I/O SystemsChapter 13: I/O Systems
I/O HardwareApplication I/O InterfaceKernel I/O SubsystemTransforming I/O Requests to Hardware OperationsStreamsPerformance
13.3 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
ObjectivesObjectives
Explore the structure of an operating system’s I/O subsystemDiscuss the principles of I/O hardware and its complexityProvide details of the performance aspects of I/O hardware and software
13.4 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
I/O HardwareI/O Hardware
Incredible variety of I/O devicesCommon concepts
PortBus (daisy chain or shared direct access)Controller (host adapter)
I/O instructions control devicesDevices have addresses, used by
Direct I/O instructionsMemory-mapped I/O
13.5 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
A Typical PC Bus StructureA Typical PC Bus Structure
13.6 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Device I/O Port Locations on PCs (partial)Device I/O Port Locations on PCs (partial)
13.7 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
PollingPolling
Determines state of device command-readybusyError
Busy-wait cycle to wait for I/O from device
13.8 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
InterruptsInterrupts
CPU Interrupt-request line triggered by I/O device
Interrupt handler receives interrupts
Maskable to ignore or delay some interrupts
Interrupt vector to dispatch interrupt to correct handlerBased on prioritySome nonmaskable
Interrupt mechanism also used for exceptions
13.9 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
InterruptInterrupt--Driven I/O CycleDriven I/O Cycle
13.10 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Intel Pentium Processor EventIntel Pentium Processor Event--Vector TableVector Table
13.11 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Direct Memory AccessDirect Memory Access
Used to avoid programmed I/O for large data movement
Requires DMA controller
Bypasses CPU to transfer data directly between I/O device and memory
13.12 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Six Step Process to Perform DMA TransferSix Step Process to Perform DMA Transfer
13.13 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Application I/O InterfaceApplication I/O Interface
I/O system calls encapsulate device behaviors in generic classesDevice-driver layer hides differences among I/O controllers from kernelDevices vary in many dimensions
Character-stream or blockSequential or random-accessSharable or dedicatedSpeed of operationread-write, read only, or write only
13.14 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
A Kernel I/O StructureA Kernel I/O Structure
13.15 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Characteristics of I/O DevicesCharacteristics of I/O Devices
13.16 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Block and Character DevicesBlock and Character Devices
Block devices include disk drivesCommands include read, write, seek Raw I/O or file-system accessMemory-mapped file access possible
Character devices include keyboards, mice, serial portsCommands include get, put
Libraries layered on top allow line editing
13.17 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Network DevicesNetwork Devices
Varying enough from block and character to have own interface
Unix and Windows NT/9x/2000 include socket interfaceSeparates network protocol from network operationIncludes select functionality
Approaches vary widely (pipes, FIFOs, streams, queues, mailboxes)
13.18 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Clocks and TimersClocks and Timers
Provide current time, elapsed time, timer
Programmable interval timer used for timings, periodic interrupts
ioctl (on UNIX) covers odd aspects of I/O such as clocks and timers
13.19 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Blocking and Nonblocking I/OBlocking and Nonblocking I/O
Blocking - process suspended until I/O completedEasy to use and understandInsufficient for some needs
Nonblocking - I/O call returns as much as availableUser interface, data copy (buffered I/O)Implemented via multi-threadingReturns quickly with count of bytes read or written
Asynchronous - process runs while I/O executesDifficult to useI/O subsystem signals process when I/O completed
13.20 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Two I/O MethodsTwo I/O Methods
Synchronous Asynchronous
13.21 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Kernel I/O SubsystemKernel I/O Subsystem
SchedulingSome I/O request ordering via per-device queueSome OSs try fairness
Buffering - store data in memory while transferring between devices
To cope with device speed mismatchTo cope with device transfer size mismatchTo maintain “copy semantics”
13.22 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
DeviceDevice--status Tablestatus Table
13.23 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Sun Enterprise 6000 DeviceSun Enterprise 6000 Device--Transfer RatesTransfer Rates
13.24 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Kernel I/O SubsystemKernel I/O Subsystem
Caching - fast memory holding copy of dataAlways just a copyKey to performance
Spooling - hold output for a deviceIf device can serve only one request at a time i.e., Printing
Device reservation - provides exclusive access to a deviceSystem calls for allocation and deallocationWatch out for deadlock
13.25 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Error HandlingError Handling
OS can recover from disk read, device unavailable, transient write failures
Most return an error number or code when I/O request fails
System error logs hold problem reports
13.26 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
I/O ProtectionI/O Protection
User process may accidentally or purposefully attempt to disruptnormal operation via illegal I/O instructions
All I/O instructions defined to be privilegedI/O must be performed via system calls
Memory-mapped and I/O port memory locations must be protected too
13.27 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Use of a System Call to Perform I/OUse of a System Call to Perform I/O
13.28 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Kernel Data StructuresKernel Data StructuresKernel keeps state info for I/O components, including open file
Many, many complex data structures to track buffers, memory
Some use object-oriented methods and message passing to
13.29 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
UNIX I/O Kernel StructureUNIX I/O Kernel Structure
13.30 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
I/O Requests to Hardware OperationsI/O Requests to Hardware Operations
Consider reading a file from disk for a process:
Determine device holding file Translate name to device representationPhysically read data from disk into bufferMake data available to requesting processReturn control to process
13.31 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Life Cycle of An I/O RequestLife Cycle of An I/O Request
13.32 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
STREAMSSTREAMS
STREAM – a full-duplex communication channel between a user-level process and a device in Unix System V and beyond
A STREAM consists of:- STREAM head interfaces with the user process- driver end interfaces with the device- zero or more STREAM modules between them.
Each module contains a read queue and a write queue
Message passing is used to communicate between queues
13.33 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
The STREAMS StructureThe STREAMS Structure
13.34 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
PerformancePerformance
I/O a major factor in system performance:
Demands CPU to execute device driver, kernel I/O codeContext switches due to interruptsData copyingNetwork traffic especially stressful
13.35 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Intercomputer CommunicationsIntercomputer Communications
13.36 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Improving PerformanceImproving Performance
Reduce number of context switchesReduce data copying Reduce interrupts by using large transfers, smart controllers, polling Use DMABalance CPU, memory, bus, and I/O performance for highest throughput
13.37 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
DeviceDevice--Functionality ProgressionFunctionality Progression
End of Chapter 13End of Chapter 13