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Slide 5-1
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-2
Device
Management
Copyright © 2004 Pearson Education, Inc.
5
Operating Systems: A Modern Perspective, Chapter 5
Input/Output Devices
Slide 5-3
Output Device
Input Device
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Processor
Operating Systems: A Modern Perspective, Chapter 5
The Device Driver Interface
…
write(…);
…
Device Interface
Terminal
Driver
Printer
Driver
Disk
Driver
Terminal
Controller
Printer
Controller
Disk
Controller
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-4
Slide 5-5
Device Management Organization
Application
Process
System Interface
File
Manager
Device-Independent
Device-Dependent
Hardware Interface
Command
Status
Data
Device Controller
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
System Call Interface
• Functions available to application programs
• Abstract all devices (and files) to a few
interfaces
• Make interfaces as similar as possible
– Block vs character
– Sequential vs direct access
• Device driver implements functions (one
entry point per API function)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-6
Example: BSD UNIX Driver
open
close
ioctl
read
write
strategy
select
stop
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Prepare dev for operation
No longer using the device
Character dev specific info
Character dev input op
Character dev output op
Block dev input/output ops
Character dev check for data
Discontinue a stream output op
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-7
Overlapping the Operation of a
Device and the CPU
. . .
read(dev_I, “%d”, x);
y = f(x)
. . .
. . .
startRead(dev_I, “%d”, x);
. . .
While(stillReading()) ;
y = f(x)
. . .
Data on device
Variable x
Register
Memory
CPU
Device dev_I
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Slide 5-8
Operating Systems: A Modern Perspective, Chapter 5
Overlapping CPU-Controller
Operations in a Process
App
I/O Ctlr
t1
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t2 t3 t4
t5
t6
t7
Operating Systems: A Modern Perspective, Chapter 5
t8
t9
Slide 5-9
Overlapping Processing and I/O
App 1
App 2
I/O Ctlr
t1
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t2
t3
Operating Systems: A Modern Perspective, Chapter 5
t4
Slide 5-10
Polling I/O Read Operation
read(device, …);
1
System Interface
Data
read function
5
write function
2
3
4
Hardware Interface
Command
Status
Data
Device Controller
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-11
Interrupt-driven I/O Operation
read(device, …);
1
Slide 5-12
9
8b
Data
System Interface
Device Status Table
4
read driver
2
7
Device
Handler
write driver
6
3
Interrupt
Handler
5
Hardware Interface
Command
Status
Data
Device Controller
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
8a
Device Independent Function Call
Trap Table
funci(…)
dev_func_i(devID, …) {
// Processing common to all devices
…
switch(devID) {
case dev0: dev0_func_i(…);
break;
case dev1: dev1_func_i(…);
break;
…
case devM: devM_func_i(…);
break;
};
// Processing common to all devices
…
}
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-13
Driver-Kernel Interface
Slide 5-14
• Drivers are distinct from main part of kernel
• Kernel makes calls on specific functions,
drivers implement them
• Drivers use kernel functions for:
–
–
–
–
Device allocation
Resource (e.g., memory) allocation
Scheduling
etc. (varies from OS to OS)
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Reconfigurable Device Drivers
Slide 5-15
System call interface
open(){…}
read(){…}
Entry Points for Device j
etc.
Driver for Device j
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Other
Kernel
services
Operating Systems: A Modern Perspective, Chapter 5
Handling Interrupts
Device driver J
int read(…) {
// Prepare for I/O
save_state(J);
out dev#
// Done (no return)
}
Device status table
J
Device interrupt handler J
void dev_handler(…) {
get_state(J);
//Cleanup after op
signal(dev[j]);
return_from_sys_call();
}
Interrupt Handler
Device Controller
Copyright © 2004 Pearson Education, Inc.
Slide 5-16
Operating Systems: A Modern Perspective, Chapter 5
Handling Interrupts(2)
Device driver J
Device interrupt handler J
int read(…) {
…
out dev#
// Return after interrupt
wait(dev[J});
return_from_sys_call();
}
void dev_handler(…) {
//Cleanup after op
signal(dev[j]);
}
Interrupt Handler
Device Controller
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-17
The Pure Cycle Water Company
Customer Office
Water Company
Returning the Empties
Water Producer
Water Consumers
Delivering Water
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-18
Slide 5-19
Hardware Buffering
Process
Controller
Process
Controller
Controller
Data
A
Device
Device
Unbuffered
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Process
B
Process reads bi-1
Controller reads bi
A
B
Device
Process reads bi
Controller reads bi+1
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-20
Driver
Double Buffering in the Driver
Process
Process
A
A
B
Hardware
Controller
A
B
Device
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B
Controller
A
B
Device
Operating Systems: A Modern Perspective, Chapter 5
Circular Buffering
Buffer j
Buffer i
To data consumer
From data producer
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Operating Systems: A Modern Perspective, Chapter 5
Slide 5-21
A Generic Communications Device
Slide 5-22
Bus
Generic
Controller
Communications
Controller
Local
Device
Cabling connecting the
controller to the device
Device
•Printer
•Modem
•Network
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Operating Systems: A Modern Perspective, Chapter 5
Rotating Media
Track (Cylinder)
(a) Multi-surface Disk
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(b) Disk Surface
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-23
Cylinder
(set of tracks)
(b) Cylinders
Slide 5-24
Storage
Device
Device Driver API
Driver
• Get disk description
• Set SCSI parms
•read/write ops
• Interrupt hander
SCSI API
•commands
•bits per byte
•etc.
Controller
(SCSI)
Magnetic Disk
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Compute vs I/O Bound
Slide 5-25
Compute-bound
Time
I/O-bound
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Disk Optimizations
• Transfer Time: Time to copy bits from disk
surface to memory
• Disk latency time: Rotational delay waiting
for proper sector to rotate under R/W head
• Disk seek time: Delay while R/W head
moves to the destination track/cylinder
• Access Time = seek + latency + transfer
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-26
Optimizing Seek Time
• Multiprogramming on I/O-bound programs
=> set of processes waiting for disk
• Seek time dominates access time =>
minimize seek time across the set
• Tracks 0:99; Head at track 75, requests for
23, 87, 36, 93, 66
• FCFS: 52+ 64 + 51 + 57 + 27 = 251 steps
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-27
Optimizing Seek Time (cont)
• Requests = 23, 87, 36, 93, 66
• SSTF: (75), 66, 87, 93, 36, 23
– 11 + 21 + 6 + 57 + 13 = 107 steps
• Scan/Elevator: (75), 87, 93, 99, 66, 36, 23
– 12 + 6 + 6 + 33 + 30 + 13 = 100 steps (goes to
highest track -99 – even if no request)
• Look/Elevator: (75), 87, 93, 66, 36, 23
– 12 + 6 + 27 + 30 + 13 = 87 steps
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-28
Optimizing Seek Time (cont)
Slide 5-29
• Requests = 23, 87, 36, 93, 66
• Circular Scan/Elevator: (75), 87, 93, 99, 23,
36, 66 (always in the same direction – home
return)
– 12 + 6 + 6 + home + 23 + 13 + 30 = 90 + home
• Circular Look/Elevator: (75), 87, 93, 23, 36,
66
– 12 + 6 + home + 23 + 13 + 30 = 84 + home
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Serial Port
CPU
Memory
Serial
Device
• Printer
• Terminal
• Modem
• Mouse
• etc.
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-30
Serial Port
Slide 5-31
Device Driver API
Device Driver
Software on the CPU
• Set UART parms
•read/write ops
•Interrupt hander
UART API
•parity
•bits per byte
•etc.
Bus Interface
Serial Device
(UART)
RS-232 Interface
• 9-pin connector
• 4-wires
• bit transmit/receive
• ...
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Adding a Modem
CPU
Memory
Serial
Device
Modem
• Dialing & connecting
• Convert analog voice to/from digital
• Convert bytes to/from bit streams
• Transmit/receive protocol
Phone
Switched Telephone Network
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-32
Serial Communication
Slide 5-33
Device Driver
•Set UART parms
•read/write ops
•Interrupt hander
Driver-Modem Protocol
• Dialing & connecting
• Convert analog voice to/from digital
• Convert bytes to/from bit streams
• Transmit/receive protocol
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Serial Device
RS-232
Modem
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-34
Exploiting the Phone Network
Logical Communication
CPU
Memory
CPU
Comm
Device
Comm
Device
Modem
Modem
Phone
Phone
Switched Telephone Network
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Memory
Slide 5-35
Data Networks
• Technology focus includes protocols and software
(more on this later … Chapter 15 and beyond ...)
Logical Communication
CPU
Memory
Network
Device
Network
Device
Data Network
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
CPU
Memory
MS Disk Description
0x00
0x03
0x0b
0x0d
0x10
0x11
0x13
0x15
0x16
0x18
0x1a
0x1c
0x1e
Copyright © 2004 Pearson Education, Inc.
0x02
0x0a
0x0c
0x0f
0x10
0x12
0x14
0x15
0x17
0x19
0x1b
0x1d
…
<a jump instruction to 0x1e>
Computer manufacturer name
Sectors per cluster (MS-DOS reads/writes a cluster of sectors)
Reserved sectors for the boot record
Number of FATs
Number of root directory entries
Number of logical sectors
Medium descriptor byte (used only on old versions of MS-DOS)
Sectors per FAT
Sectors per track
Number of surfaces (heads)
Number of hidden sectors
Bootstrap program
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-36
NT Driver Organization
Data Flow
I/O Portion of Native API
Filter Driver
Intermediate Driver
Filter Driver
Device Driver
HAL
Device
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
NT Executive
I/O Manager
File System Driver
Slide 5-37
NT Device Drivers
• API model is the same as for a file
• Extend device management by adding
modules to the stream
• Device driver is invoked via an Interrupt
Request Packet (IRP)
– IRP can come from another stream module
– IRP can come from the OS
– Driver must respond to minimum set of IRPs
• See Part I of notes
Copyright © 2004 Pearson Education, Inc.
Operating Systems: A Modern Perspective, Chapter 5
Slide 5-38
Slide 5-39
Rensselaer Polytechnic Institute
CSCI-4210 – Operating Systems
David Goldschmidt, Ph.D.
Operating Systems
{week 14}
Copyright © 2004 Pearson Education, Inc.
I/O system
• The Input/Output (I/O) System has two
primary objectives:
– Handle application I/O requests
• Map logical address to physical disk or device
address
• Send response back to the application
– Optimize I/O performance
• Depends on request type and device type
Copyright © 2004 Pearson Education, Inc.
Slide 5-40
Disk drives & the disk controller
• Disks and other devices operate in parallel
to the CPU (but are much slower)
– Typical disk
drive mechanism:
– Arm seeks to the
appropriate track
– Disk rotates until
the desired sector
is accessed
Copyright © 2004 Pearson Education, Inc.
Slide 5-41
Disk access time
• Disk access time is the sum
of the seek time and the
rotational latency
– Cache surrounding
sectors or entire track
to improve performance
– Principle of locality
(again!)
Copyright © 2004 Pearson Education, Inc.
Slide 5-42
I/O system structure
Copyright © 2004 Pearson Education, Inc.
Slide 5-43
I/O request
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Slide 5-44
I/O performance optimization (i)
Slide 5-45
• Disk access times are orders of magnitude
slower than CPU execution times
• Improve I/O performance by:
–
–
–
–
do this at the
application layer
Reducing the number of I/O requests
Implementing buffering
Implementing caching
Efficiently scheduling I/O requests
Copyright © 2004 Pearson Education, Inc.
I/O performance optimization (ii)
• Use buffering to make
physical I/O requests
as large as possible
– This reduces the
number of I/O requests
– Space-time tradeoff
– Misleads programmers?
– Other disadvantages?
Copyright © 2004 Pearson Education, Inc.
Slide 5-46
Slide 5-47
I/O performance optimization (iii)
• Use caching to keep retrieved data
in fast memory for potential
future access
– Eliminates one or more
I/O requests
– Space-time tradeoff
– Principle of locality
(yet again!)
Copyright © 2004 Pearson Education, Inc.
Disk context switch
Slide 5-48
• A disk context switch occurs when
switching from one I/O request to another
– Disk context switch time is substantially higher
than process context switch
– Disk context switch time is substantially lower
than disk read/write operation
– The time to complete the nth I/O operation
depends on where the (n-1)th operation finished
Copyright © 2004 Pearson Education, Inc.
Disk I/O scheduling
• Goal: optimize disk performance
Slide 5-49
maximize throughput
ensure fairness, etc.
• Scheduling algorithm determines which
pending disk I/O request to select next:
– First-Come-First-Served (FCFS)
– Shortest Seek Time First (SSTF)
– Elevator (SCAN) and Circular SCAN (C-SCAN)
Copyright © 2004 Pearson Education, Inc.
First-come-first-served (FCFS)
Slide 5-50
• Request reference string specifies requested
44, 20, 95, 4, 50, 52, 47, 61, 87, 25
tracks:
Copyright © 2004 Pearson Education, Inc.
First-come-first-served (FCFS)
Slide 5-51
• Request reference string specifies requested
98, 183, 37, 122, 14, 124, 65, 67
tracks:
Copyright © 2004 Pearson Education, Inc.
Shortest seek time first (SSTF)
Slide 5-52
• Request reference string specifies requested
44, 20, 95, 4, 50, 52, 47, 61, 87, 25
tracks:
Copyright © 2004 Pearson Education, Inc.
Shortest seek time first (SSTF)
Slide 5-53
• Request reference string specifies requested
98, 183, 37, 122, 14, 124, 65, 67
tracks:
Copyright © 2004 Pearson Education, Inc.
Elevator (SCAN)
Slide 5-54
• Request reference string specifies requested
44, 20, 95, 4, 50, 52, 47, 61, 87, 25
tracks:
repeated end-to-end scans
Copyright © 2004 Pearson Education, Inc.
Elevator (SCAN)
Slide 5-55
• Request reference string specifies requested
98, 183, 37, 122, 14, 124, 65, 67
tracks:
Copyright © 2004 Pearson Education, Inc.
Circular SCAN and LOOK
Slide 5-56
• Circular SCAN (C-SCAN) scans in one direction
– When it reaches one end of the disk, it returns
to the beginning of the disk without servicing
any requests on the return trip
• LOOK (and C-LOOK) algorithms
– Disk arm moves in one direction as long as
there are pending requests in that direction
– Otherwise, it reverses direction immediately
Copyright © 2004 Pearson Education, Inc.