操作系统原理13章节(1285KB).ppt

Performance I/O a major factor in system performance: Demands CPU to execute device driver, kernel I/O code Context switches due to interrupts Data copying Network traffic especially stressful Improving Performance Reduce number of context switches Reduce data copying Reduce interrupts by using large transfers, smart controllers, polling Use DMA Balance CPU, memory, bus, and I/O performance for highest throughput Device-Functionality Progression * Chapter 13: I/O Systems 张竞慧 jhzhang@seu.edu.cn Chapter 13: I/O Systems I/O Hardware Application I/O Interface Kernel I/O Subsystem Transforming I/O Requests to Hardware Operations Streams Performance I/O Hardware Incredible variety of I/O devices Common concepts Port Bus (daisy chain or shared direct access) Controller (host adapter) I/O instructions control devices Devices have addresses, used by Direct I/O instructions Memory-mapped I/O A Typical PC Bus Structure Device I/O Port Locations on PCs (partial) Polling Determines state of device command-ready busy Error Busy-wait cycle to wait for I/O from device Interrupts 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 handler Based on priority Some nonmaskable Interrupt mechanism also used for exceptions Interrupt-Driven I/O Cycle Intel Pentium Processor Event-Vector Table Direct 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 Six Step Process to Perform DMA Transfer Application I/O Interface I/O system calls encapsulate device behaviors in generic classes Device-driver layer hides differences among I/O controllers from kernel Devices vary in many dimensions Character-stream or block Sequential or random-access Sharable or dedicated Speed of operation read-write, read only, or write only A Kernel I/O Structure Charact