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COMPUTER SYSTEMS
An Integrated Approach to Architecture and Operating Systems
Chapter 10
Input/Output and Stable Storage
©Copyright 2008 Umakishore Ramachandran and William D. Leahy Jr.
10.1 Communication between the CPU
and the I/O devices
Computer
Device Controller
Input/Output
Device
10.1.1 Device controller
10.1.2 Memory Mapped I/O
CPU
Address
Data
7
0
Main memory
Data register
(address = 5000)
7
Ready
0
IF
…
IE
Status register
(address = 5002)
Keyboard controller
10.2 Programmed I/O
10.3 DMA
CPU
Memory bus
DMA controller
Status
Go
Command
Memory
Device address
Memory buffer address
Count
256 bytes
Buffer
10.4 Buses
• System Bus (or Memory Bus) is key resource in
entire design.
• Functionally, bus has following components:
– Address lines
– Data lines
– Command lines
– Interrupt lines
– Interrupt acknowledge lines
– Bus arbitration lines
10.4 Buses
CPU
System bus
Bridge
Memory
PCI bus
Controller
Controller
Controller
10.5 I/O Processor
CPU
I/O processor
System bus
Bridge
I/O bus
Shared
Memory
Controller
Controller
Controller
10.6 Device Driver
10.6.1 An Example
Command
pan(±ɵ)
tilt(±ɵ)
zoom(±z)
Start
Stop
memory
buffer(M)
number of
frames (N)
enable interrupt
disable
interrupt
start DMA
Controller Action
Pan the camera view by ±ɵ
Tilt camera position by ±ɵ
Zoom camera focus by ±z
Start camera
Stop camera
Set memory buffer address for data
transfer to M
Set number of frames to be captured
and transferred to memory to N
Enable interrupt from the device
Disable interrupt from the device
Start DMA data transfer from
camera
10.6.1 An Example
// device driver: camera
// The device driver performs several functions:
//
control_camera_position;
//
convey_DMA_parameters;
//
start/stop data transfer;
//
interrupt_handler;
//
error handling and reporting;
// Control camera position
camera_position_control
(angle pan_angle; angle tilt_angle; int z) {
pan(pan_angle);
tilt(tilt_angle);
zoom(z);
}
// Set up DMA parameters for data transfer
camera_DMA_parameters(address mem_buffer;int num_frames) {
memory_buffer(mem_buffer);
capture_frames(num_frames);
}
10.6.1 An Example
// Start DMA transfer
camera_start_data_transfer() {
start_camera();
start_DMA();
}
// Stop DMA transfer
camera_stop_data_transfer() {
// automatically aborts data transfer
// if camera is stopped;
stop_camera();
}
// Enable interrupts from the device
camera_enable_interrupt() {
enable_interrupt();
}
// Disable interrupts from the device
camera_disable_interrupt() {
disable_interrupt();
}
10.6.1 An Example
// Device interrupt handler
camera_interrupt_handler() {
// This will be coded similar to any
// interrupt handler we have seen in
// chapter 4.
//
// The upshot of interrupt handling may
// to deliver “events” to the upper layers
// of the system software (see Figure 10.9)
// which may be one of the following:
// - normal I/O request completion
// - device errors for the I/O request
//
}
10.7 Peripheral Devices
Device
Input/output
Human in
the loop
Yes
Yes
No
No
Data rate (circa
2008)
5-10 bytes/sec
80-200 bytes/sec
200-350 MB/sec
100-200 MB/sec
PIO
DMA
Keyboard
Mouse
Graphics display
Disk (hard drive)
Input
Input
Output
Input/Output
X
X
Network (LAN)
Input/Output
No
1 Gbit/sec
X
Modem
Input/Output
No
1-8 Mbit/sec
X
Inkjet printer
Laser printer
Voice
(microphone/speaker)
Audio (music)
Flash memory
Output
Output
Input/Output
No
No
Yes
20-40 KB/sec
200-400 KB/sec
10 bytes/sec
Output
Input/Output
No
No
4-500 KB/sec
10-50 MB/sec
X
X
CD-RW
Input/Output
No
10-20 MB/sec
X
DVD-R
Input
No
10-20 MB/sec
X
X
X
X
X
X
X
10.8 Disk Storage
Shaft
Head
Track
Spindle
Sector
Arm
Head
Assembly
All heads move
together
Platter
Top and bottom
Surfaces
10.8 Disk Storage
Each circle represents
two tracks: one for top surface
and one for bottom surface
Cylinder X: Track X
from all 12 surfaces
(2 per platter)
10.8 Disk Storage
(a) Normal (Non zoned) recording
(b) Zoned recording
10.8.1 Saga of Disk Technology
Disk recording: (a) Longitudinal recording; (b) PMR
10.9 Disk Scheduling Algorithms
Name
Notation
Units
Throughput
n/T
Jobs/sec System-centric
metric quantifying
the number of I/O
requests n
executed in time
interval T
Avg.
Turnaround
time (tavg)
(t1+t2+…+tn)/n
Seconds System-centric
metric quantifying
the average time it
takes for a job to
complete
Avg. Waiting
time (wavg)
((t1-e1) + (t2-e2)+ … +
(tn-en))/n
or
(w1+w2+ … +wn)/n
Seconds System-centric
metric quantifying
the average waiting
time that an I/O
request experiences
ti
Seconds User-centric metric
quantifying the
turnaround time for
a specific I/O
request i
Response
time/
turnaround
time
Description
Name
Variance in
Response
time
Notation
E[(ti – tavg)2]
Variance in
Wait time
E[(wi – wavg)2]
Starvation
-
Units
Description
Seconds User-centric metric
2
that quantifies the
statistical variance
of the actual
response time (ti)
experienced by an
I/O request i from
the expected value
(tavg)
Seconds User-centric metric
2
that quantifies the
statistical variance
of the actual wait
time (wi)
experienced by an
I/O request i from
the expected value
(wavg)
User-centric
qualitative metric
that signifies denial
of service to a
particular I/O
request or a set of
I/O request due to
some intrinsic
property of the I/O
scheduler
Assumptions for
Disk Scheduling Algorithms
• Disk has 200 tracks numbered 0 to 199
– (with 0 being outermost and 199 being
innermost).
• Head when in its fully retracted position is on
track 0.
• Head assembly extends to its maximum span
from its resting position when it is on track
199.
10.9.1 First-Come First Served
t3
t1
head
t4
t2
10.9.2 Shortest Seek Time First
t3
t1
head
t4
t2
10.9.3 Scan (elevator algorithm)
Outermost
track
head t3
Innermost
track
t4
t1
t6
t5
t2
10.9.4 C-Scan (Circular Scan)
Outermost track
Innermost
track
head t3
t4
t1
Retract
t6
t5
t2
10.9.5 Look and C-Look
10.9.6 Disk Scheduling Summary
• Choice of scheduling algorithm depends on a
number of factors including expected layout,
storage allocation policy, and electromechanical capabilities of disk drive.
• Typically, some variant of LOOK or C-LOOK is
used for disk scheduling. We covered other
algorithms more from the point of
completeness than as viable choices for
implementation in a real system.
10.9.7 Comparison of the Algorithms
Requests
Response time
FCFS
SSFT
R1 (cyl 20)
R2 (cyl 17)
R3 (cyl 55)
R4 (cyl 35)
R5 (cyl 25)
R6 (cyl 78)
R7 (cyl 99)
Average
3
6
44
64
74
127
148
66.4
7
10
48
28
2
71
92
36
LOOK
155
158
32
12
2
55
76
70
10.10 Solid State Drive
10.11 Evolution of I/O Buses and
Device Drivers
•
•
•
Plug and Play (Solves 3rd party problem)
Parallel Buses (e.g. PCI)
Serial Buses
– USB (Microsoft/Intel)
• USB 1.0: 1.5Mb/s
• USB 2.0: 60Mb/s
– Firewire (Apple)
• 100 Mb/s
– Why serial?
•
•
•
•
•
Smaller
Cheaper
No cross-talk
Serial signaling can be operated faster than parallel (Higher frequencies)
Graphics Connections (connecting 3-D graphics controller card to motherboard)
–
–
Advanced Graphics Port (AGP)
PCI Express (PCI-e)
10.11.1 Dynamic Loading of Device
Drivers
• Device drivers can be Plug and Play
• New device is connected, generates interrupt
• OS looks through its list of device drivers and
finds correct one*
• Dynamically Loads and links driver into
memory
*If no driver found has to request user supply driver
10.11.2 Putting it all Together
10.11.2 Putting it all Together
10.12 Summary
• Mechanisms for communication between
processor and I/O devices including
programmed I/O and DMA.
• Device controllers and device drivers.
• Buses in general and evolution of I/O buses in
particular, found in modern computer
systems.
• Disk storage and disk-scheduling algorithms.