Bài giảng Hệ điều hành nâng cao - Chapter 13: I/O systems trình bày về I/O hardware, application I/O interface, kernel I/O subsystem, transforming I/O requests to hardware operations, STREAMS, performance.
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Nội dung Text: Bài giảng Hệ điều hành nâng cao - Chapter 13: I/O Systems
- Chapter 13: I/O Systems
Operating System Concepts – 8th8th Edition
Operating System Concepts – Edition 13.1 Silberschatz, Galvin and Gagne ©2009
- Chapter 13: I/O Systems
s I/O Hardware
s Application I/O Interface
s Kernel I/O Subsystem
s Transforming I/O Requests to Hardware Operations
s STREAMS
s Performance
Operating System Concepts – 8th Edition 13.2 Silberschatz, Galvin and Gagne ©2009
- Objectives
s Explore the structure of an operating system’s I/O subsystem
s Discuss the principles of I/O hardware and its complexity
s Provide details of the performance aspects of I/O hardware and software
Operating System Concepts – 8th Edition 13.3 Silberschatz, Galvin and Gagne ©2009
- Overview
s I/O management is a major component of operating system design and operation
q Important aspect of computer operation
q I/O devices vary greatly
q Various methods to control them
q Performance management
q New types of devices frequent
s Ports, busses, device controllers connect to various devices
s Device drivers encapsulate device details
q Present uniform device-access interface to I/O subsystem
Operating System Concepts – 8th Edition 13.4 Silberschatz, Galvin and Gagne ©2009
- I/O Hardware
s Incredible variety of I/O devices
q Storage
q Transmission
q Human-interface
s Common concepts – signals from I/O devices interface with computer
q Port – connection point for device
q Bus - daisy chain or shared direct access
q Controller (host adapter) – electronics that operate port, bus, device
4 Sometimes integrated
4 Sometimes separate circuit board (host adapter)
4 Contains processor, microcode, private memory, bus controller, etc
– Some talk to per-device controller with bus controller, microcode, memory, etc
Operating System Concepts – 8th Edition 13.5 Silberschatz, Galvin and Gagne ©2009
- A Typical PC Bus Structure
Operating System Concepts – 8th Edition 13.6 Silberschatz, Galvin and Gagne ©2009
- I/O Hardware (Cont.)
s I/O instructions control devices
s Devices usually have registers where device driver places commands, addresses, and data to write, or read data
from registers after command execution
q Data-in register, data-out register, status register, control register
q Typically 1-4 bytes, or FIFO buffer
s Devices have addresses, used by
q Direct I/O instructions
q Memory-mapped I/O
4 Device data and command registers mapped to processor address space
4 Especially for large address spaces (graphics)
Operating System Concepts – 8th Edition 13.7 Silberschatz, Galvin and Gagne ©2009
- Device I/O Port Locations on PCs (partial)
Operating System Concepts – 8th Edition 13.8 Silberschatz, Galvin and Gagne ©2009
- Polling
s For each byte of I/O
1. Read busy bit from status register until 0
2. Host sets read or write bit and if write copies data into data-out register
3. Host sets command-ready bit
4. Controller sets busy bit, executes transfer
5. Controller clears busy bit, error bit, command-ready bit when transfer done
s Step 1 is busy-wait cycle to wait for I/O from device
q Reasonable if device is fast
q But inefficient if device slow
q CPU switches to other tasks?
4 But if miss a cycle data overwritten / lost
Operating System Concepts – 8th Edition 13.9 Silberschatz, Galvin and Gagne ©2009
- Interrupts
s Polling can happen in 3 instruction cycles
q Read status, logical-and to extract status bit, branch if not zero
q How to be more efficient if non-zero infrequently?
s CPU Interrupt-request line triggered by I/O device
q Checked by processor after each instruction
s Interrupt handler receives interrupts
q Maskable to ignore or delay some interrupts
s Interrupt vector to dispatch interrupt to correct handler
q Context switch at start and end
q Based on priority
q Some nonmaskable
q Interrupt chaining if more than one device at same interrupt number
Operating System Concepts – 8th Edition 13.10 Silberschatz, Galvin and Gagne ©2009
- Interrupt-Driven I/O Cycle
Operating System Concepts – 8th Edition 13.11 Silberschatz, Galvin and Gagne ©2009
- Intel Pentium Processor Event-Vector Table
Operating System Concepts – 8th Edition 13.12 Silberschatz, Galvin and Gagne ©2009
- Interrupts (Cont.)
s Interrupt mechanism also used for exceptions
q Terminate process, crash system due to hardware error
s Page fault executes when memory access error
s System call executes via trap to trigger kernel to execute request
s Multi-CPU systems can process interrupts concurrently
q If operating system designed to handle it
s Used for time-sensitive processing, frequent, must be fast
Operating System Concepts – 8th Edition 13.13 Silberschatz, Galvin and Gagne ©2009
- Direct Memory Access
s Used to avoid programmed I/O (one byte at a time) for large data movement
s Requires DMA controller
s Bypasses CPU to transfer data directly between I/O device and memory
s OS writes DMA command block into memory
q Source and destination addresses
q Read or write mode
q Count of bytes
q Writes location of command block to DMA controller
q Bus mastering of DMA controller – grabs bus from CPU
q When done, interrupts to signal completion
Operating System Concepts – 8th Edition 13.14 Silberschatz, Galvin and Gagne ©2009
- Six Step Process to Perform DMA Transfer
Operating System Concepts – 8th Edition 13.15 Silberschatz, Galvin and Gagne ©2009
- Application I/O Interface
s I/O system calls encapsulate device behaviors in generic classes
s Device-driver layer hides differences among I/O controllers from kernel
s New devices talking already-implemented protocols need no extra work
s Each OS has its own I/O subsystem structures and device driver frameworks
s Devices vary in many dimensions
q Character-stream or block
q Sequential or random-access
q Synchronous or asynchronous (or both)
q Sharable or dedicated
q Speed of operation
q read-write, read only, or write only
Operating System Concepts – 8th Edition 13.16 Silberschatz, Galvin and Gagne ©2009
- A Kernel I/O Structure
Operating System Concepts – 8th Edition 13.17 Silberschatz, Galvin and Gagne ©2009
- Characteristics of I/O Devices
Operating System Concepts – 8th Edition 13.18 Silberschatz, Galvin and Gagne ©2009
- Characteristics of I/O Devices (Cont.)
s Subtleties of devices handled by device drivers
s Broadly I/O devices can be grouped by the OS into
q Block I/O
q Character I/O (Stream)
q Memory-mapped file access
q Network sockets
s For direct manipulation of I/O device specific characteristics, usually an escape / back door
q Unix ioctl() call to send arbitrary bits to a device control register and data to device data register
Operating System Concepts – 8th Edition 13.19 Silberschatz, Galvin and Gagne ©2009
- Block and Character Devices
s Block devices include disk drives
q Commands include read, write, seek
q Raw I/O, direct I/O, or file-system access
q Memory-mapped file access possible
4 File mapped to virtual memory and clusters brought via demand paging
q DMA
s Character devices include keyboards, mice, serial ports
q Commands include get(), put()
q Libraries layered on top allow line editing
Operating System Concepts – 8th Edition 13.20 Silberschatz, Galvin and Gagne ©2009
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