Operating systems. Module 15 kernel I/O subsystem. Tami Sorgente 1

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1 Operating systems Mdule 15 kernel I/O subsystem Tami Srgente 1

2 SWAP SPACE MANAGEMENT Swap space can be defined as a temprary strage lcatin that is used when system s memry requirements exceed the size f available RAM. Swap-space can be carved ut f the nrmal file system, r, mre cmmnly, it can be in a separate disk partitin Tami Srgente 2

3 I/O SYSTEM OVERVIEW I/O management is a majr cmpnent f perating system design and peratin Imprtant aspect f cmputer peratin I/O devices vary greatly Varius methds t cntrl them Perfrmance management New types f devices Prts, busses, device cntrllers cnnect t varius devices Device drivers encapsulate device details Present unifrm device-access interface t I/O subsystem Tami Srgente 3

4 I/O HARDWARE Incredible variety f I/O devices Strage Transmissin Human-interface Cmmn cncepts signals frm I/O devices interface with cmputer Prt cnnectin pint fr device Bus - daisy chain r shared direct access Cntrller (hst adapter) electrnics that perate prt, bus, device Smetimes integrated Smetimes separate circuit bard (hst adapter) Prcessr, micrcde, private memry, bus cntrller, etc Tami Srgente 4

5 A TYPICAL PC BUS STRUCTURE Tami Srgente 5

6 I/O TECHNIQUES: (HOST I/O CONTROLLER COMMUNICATIONS) Plling technique actively sampling the status f an external device Like busy waiting Interrupt technique CPU Interrupt-request line triggered by I/O device Checked by prcessr after each instructin Interrupt handler receives interrupts Maskable t ignre r delay sme interrupts Interrupt vectr t dispatch interrupt t crrect handler Cntext switch at start and end Based n pririty Sme nnmaskable Tami Srgente 6

7 INTERRUPT-DRIVEN I/O CYCLE Tami Srgente 7

8 INTERRUPTS (CONT.) Interrupt mechanism als used fr exceptins Terminate prcess, crash system due t hardware errr Page fault executes when memry access errr System call executes via trap t trigger kernel t execute request Multi-CPU systems can prcess interrupts cncurrently If perating system designed t handle it Tami Srgente 8

9 DIRECT MEMORY ACCESS Used t avid prgrammed I/O (ne byte at a time) fr large data mvement Requires DMA cntrller Bypasses CPU t transfer data directly between I/O device and memry OS writes DMA cmmand blck int memry Surce and destinatin addresses Read r write mde Cunt f bytes Writes lcatin f cmmand blck t DMA cntrller When dne, interrupts t signal cmpletin Tami Srgente 9

10 SIX STEP PROCESS TO PERFORM DMA TRANSFER Tami Srgente 10

11 APPLICATION I/O INTERFACE I/O system calls encapsulate device behavirs in generic classes Device-driver layer hides differences amng I/O cntrllers Each OS has its wn I/O subsystem structures and device driver framewrks Devices vary in many dimensins Character-stream r blck Sequential r randm-access Synchrnus r asynchrnus (r bth) Sharable r dedicated Speed f peratin read-write, read nly, r write nly Tami Srgente 11

12 A KERNEL I/O STRUCTURE Tami Srgente 12

13 KERNEL I/O SUBSYSTEM Scheduling Sme I/O request rdering via per-device queue Sme OSs try fairness Buffering - stre data in memry while transferring between devices T cpe with device speed mismatch T cpe with device transfer size mismatch Duble buffering tw cpies f the data Tami Srgente 13

14 KERNEL I/O SUBSYSTEM Caching - faster device hlding cpy f data Always just a cpy Key t perfrmance Smetimes cmbined with buffering Spling - hld utput fr a device If device can serve nly ne request at a time i.e., Printing Device reservatin - prvides exclusive access t a device System calls fr allcatin and de-allcatin Watch ut fr deadlck Tami Srgente 14

15 ERROR HANDLING OS can recver frm disk read, device unavailable, transient write failures Retry a read r write, fr example Track errr frequencies, stp using device with increasing frequency f retry-able errrs Mst return an errr number r cde when I/O request fails System errr lgs hld prblem reprts Tami Srgente 15

16 KERNEL DATA STRUCTURES Kernel keeps state inf fr I/O cmpnents, including pen file tables, netwrk cnnectins, character device state Many, many cmplex data structures t track buffers, memry allcatin, dirty blcks Sme use bject-riented methds and message passing t implement I/O Tami Srgente 16

17 IMPROVING PERFORMANCE Reduce number f cntext switches Reduce data cpying Reduce interrupts by using large transfers, smart cntrllers, plling Use DMA Use smarter hardware devices Balance CPU, memry, bus, and I/O perfrmance fr highest thrughput Tami Srgente 17

CS4500/5500 Operating Systems Computer and Operating Systems Overview

CS4500/5500 Operating Systems Computer and Operating Systems Overview Operating Systems Cmputer and Operating Systems Overview Yanyan Zhuang Department f Cmputer Science http://www.cs.uccs.edu/~yzhuang UC. Clrad Springs Ref. MOS4E, OS@Austin, Clumbia, UWisc Overview Recap