Transcript No Slide Title

Distributed Operating Systems
CS551
Colorado State University
at Lockheed-Martin
Lecture 2 -- Spring 2001
CS551: Lecture 2

Topics
–
–
–
–
–
–
–
31 January 2001
Interconnection Networks
Transparencies
Real Time Systems (and networks)
Parallel Systems (architecture; software)
Kernel of a Distributed Operating System
Processes and Threads
Interprocess Communication
CS-551, Lecture 2
2
Interconnection networks

A distributed system: “a collection of
autonomous computers linked by a
computer network with distributed system
software” Coulouris, Dollimore & Kindberg,
Distributed Systems: Concepts and Design, 2nd ed.,
Addison-Wesley (1994).

Interconnection network designs
–
31 January 2001
bus, crossbar, hypercube, shuffle-exchange
CS-551, Lecture 2
3
Figure 1.8 An Interconnection
Network in a Multiprocessor.
(Galli,p.20)
31 January 2001
CS-551, Lecture 2
4
Interconnection network: Bus
Simple, static
 Shared by all attached processors
 No routing required
 All data transmissions occur on bus
 Scalability limited by bandwidth
 Examples:

–
–
31 January 2001
Encore Multimax
Sequent Balance and Sequent Symmetry
CS-551, Lecture 2
5
Figure 1.9 A Bus Used as an
Interconnection Network. (Galli,
p.20)
31 January 2001
CS-551, Lecture 2
6
Interconnection network: Crossbar
Permits dynamic configurations
 n memory modules x n processors
 Requires O(n^2) switches (expensive)


Many paths from one processor to another
31 January 2001
CS-551, Lecture 2
7
Figure 1.10 A Crossbar
Interconnection Network.
(Galli,
p.22)
31 January 2001
CS-551, Lecture 2
8
Interconnection network: Hypercube
Static
 Requires 2^k switches for k processors
 Each switch is within a processor node
 Distance between nodes easy to compute

31 January 2001
CS-551, Lecture 2
9
Figure 1.11 A Hypercube Interconnection Network of Order 3.
(Galli.p.22)
31 January 2001
CS-551, Lecture 2
10
Interconnection network:
Shuffle-Exchange
Permits dynamic reconfiguration
 Switches have four modes of operation

–

Simple routing
–

controlled by control bits in switch
address bits used as control bits
Examples:
–
31 January 2001
Benes, Banyan, Omega, Theta
CS-551, Lecture 2
11
Figure 1.12 A 2x2 Switch Box in a
Shuffle-Exchange Interconnection
Network. (Galli,p.23)
31 January 2001
CS-551, Lecture 2
12
Figure 1.13 A Perfect Shuffle.
(Galli,p.24)
31 January 2001
CS-551, Lecture 2
13
Figure 1.14 A Multistage ShuffleExchange Interconnection Network.
(Galli,p.24)
31 January 2001
CS-551, Lecture 2
14
Distributed Systems: Characteristics
Shared resources
 Openness
 Concurrency
 Scalability
 Fault tolerance
 Transparency

31 January 2001
CS-551, Lecture 2
15
D.S. Characteristics: Openness
“a characteristic that enables systems to be
extended to meet new application
requirements and user needs” (CDK, p.12)
 “achieved by specifying and documenting
the key software interfaces of a system and
making them available to software
developers; i.e. the interfaces are
published” (CDK, p.14)

31 January 2001
CS-551, Lecture 2
16
D.S. Characteristics: Transparency
“the concealment from the user and from
the application programmer of the
separation of components in a distributed
system, so that the system is perceived as a
whole rather than as a collection of
independent components” (CDK, p.20)
 Nine types:

–
access, location, concurrency, replication,
failure, migration, name, performance, scaling
31 January 2001
CS-551, Lecture 2
17
Network transparency
Network transparency = access
transparency + location transparency
 Access transparency “enables local and
remote information objects to be accessed
using identical operations” (CDK, p.20)
Location transparency “enables
information objects to be accessed without
knowledge of their location” (CDK, p.20)

31 January 2001
CS-551, Lecture 2
18
Concurrency transparency

Concurrency and parallelism
transparency
–
–
–
31 January 2001
“enables several processes to operate
concurrently using shared information objects
without interference between them” (CDK, p.20)
permits efficient use of shared resources
no interference between processes sharing
resources
CS-551, Lecture 2
19
Replication transparency

Replication transparency
–
–
–
31 January 2001
“enables multiple instances of information
objects to be used to increase reliability and
performance without knowledge of the replicas
by users of application programs” (CDK, p.20)
may be multiple copies of files in the system
updates to such files can be a problem
CS-551, Lecture 2
20
Failure transparency

Failure transparency
–
–
31 January 2001
“enables the concealment of faults, allowing
users and application programs to complete
their tasks despite the failure of hardware or
software components” (CDK, p.20)
if a site goes down, it is unapparent to other
sites -- and work continues
CS-551, Lecture 2
21
Migration transparency

Migration transparency
–
–
31 January 2001
“allows the movement of information objects
within a system without affecting the operation
of users or application programs” (CDK, p.21)
both resources and processes can migrate
without users knowing
CS-551, Lecture 2
22
Name transparency

Name transparency
–
–
–
31 January 2001
system incorporates a global naming scheme
objects (files, resources) are not tied to given
nodes or sites by name
assists migration, access, and location
transparencies
CS-551, Lecture 2
23
Performance and Scaling
transparencies

Performance transparency
–

“allows the system to be reconfigured to
improve performance as loads vary” (CDK, p.21)
Scaling transparency
–
31 January 2001
“allows the system and applications to expand
in scale without change to the system structure
or the application algorithms” (CDK, p.21)
CS-551, Lecture 2
24
Distributed Operating Systems

A distributed operating system is
–
31 January 2001
“a collection of software components that
simplifies the task of programming and
supports the widest possible range of
applications” (CDK, p.5)
CS-551, Lecture 2
25
Kernel of an operating system

The privileged portion of the OS
–

complete access to all resources
controls
–
–
–
–
31 January 2001
process management
process migration
process scheduling
address space
CS-551, Lecture 2
26
Types of OS kernels

Monolithic kernel
–
–

Layered kernel
–

Unix, OS/360, VMS
every node doesn’t need entire kernel in DOS
Windows NT/2000, Mach, Chorus (JavaOS)
Collective kernel in DOS
–
–
31 January 2001
O.S. services are processes
microkernel supports messages between such
processes
CS-551, Lecture 2
27
Figure 2.1 Microkernel Design.
(Galli,p.32)
31 January 2001
CS-551, Lecture 2
28
Processes

Process
–
–
–
–
–
a program whose execution has started, but not
terminated
has state (ready, running, waiting)
has a single address space
may run serially or concurrently
may interact with other processes via


–
shared memory
message passing
is a single thread of control
31 January 2001
CS-551, Lecture 2
29
Figure 2.4 Process States.
(Galli,p.39)
31 January 2001
CS-551, Lecture 2
30
Threads

Thread
–
–
–
–
–
is a lightweight process
has state
may share address space with other threads
may run serially or concurrently
interacts with other threads via
 shared
address space
 message passing
31 January 2001
CS-551, Lecture 2
31
Figure 2.2 A Multithreaded
Process. (Galli,p.34)
31 January 2001
CS-551, Lecture 2
32
Issues with processes and threads

Shared memory space
–
–

no protection barrier to other processes/threads
need to maintain integrity
Synchronized access
–
–
31 January 2001
must enforce mutual exclusion
code that accesses a shared resource must be a
critical section
CS-551, Lecture 2
33
Multi-threaded systems

Three models
–
–
–

specialist -- all threads equal
client/server -- server allots tasks to clients
assembly line -- like a pipeline
Supporting
–
–
31 January 2001
POSIX
Java
CS-551, Lecture 2
34
Figure 2.3 Multithreaded
Process Paradigms. (Galli,p.35)
31 January 2001
CS-551, Lecture 2
35
Why threads?

Processes
–
to create or destroy a process is expensive
 requires
–
to restore or swap out a process is expensive
 requires

more memory space
memory map changes
Threads
–
–
31 January 2001
can keep a pool of threads and reuse them
memory space is shared and need not always be
swapped
CS-551, Lecture 2
36
Process management
Controls process (or thread) and its
components
 Recall PCB (Process Control Block)

–
–
–
–
–
–
31 January 2001
process id
process state
process priority
process privileges
virtual memory address
recorded statistics for account
CS-551, Lecture 2
37
Figure 2.4 Process States.
(Galli,p.39)
31 January 2001
CS-551, Lecture 2
38
Processes, continued

Indivisible
–
–

Divisible
–
–
–

independent
not divisible into smaller tasks
may be broken up into smaller processes (tasks)
subtasks may run on different nodes
helps to balance load of distributed system
Task Interaction Graphs (TIG)
31 January 2001
CS-551, Lecture 2
39
Example of TIG

TIG shows precedence of subtasks
–
–
–
–
–
–
31 January 2001
T1 -- Prepare main course
T2 -- Prepare side dishes
T3 -- Prepare dessert
T4 -- Set table
T5 -- Serve meal
T6 -- Serve dessert
CS-551, Lecture 2
40
Figure 2.5 TIG Revealing
Precedence Relationships.
(Galli,p.42)
31 January 2001
CS-551, Lecture 2
41
Load Distribution

Goal
–

Load balancing
–

to balance the load equally among resources
Load sharing
–

to utilize resources in an efficient manner
to relieve overloaded resources
Process migration
–
31 January 2001
to move a process to another processor
CS-551, Lecture 2
42
Load distribution algorithms
Two parts
 Information-gathering

–

status states (site is overloaded/underutilized?)
Process selection
–
–
–
31 January 2001
which process/thread/task to migrate?
expected overhead for migration?
expected execution time?
CS-551, Lecture 2
43
Heterogeneous environments

May include different data representations
–

process migration may require data translation
External data representation
–
31 January 2001
common data representation between sites
CS-551, Lecture 2
44
Figure 2.6 Data Translation
without External Data
Representation. (Galli, p.44)
31 January 2001
CS-551, Lecture 2
45
Figure 2.7 Data Translation with
External Data Representation.
(Galli,p.44)
31 January 2001
CS-551, Lecture 2
46
Process Scheduling
Recall from Operating Systems course
 Problem: #2.10 in textbook
 Identifying schedulable tasks

–
–
–
31 January 2001
polled loop
interrupts
gang scheduling
CS-551, Lecture 2
47
Figure 2.8 Polled-Loop
Example. (Galli,p.47)
31 January 2001
CS-551, Lecture 2
48
Figure 2.9 Smart Concurrent
Scheduling. (Galli,p.48)
31 January 2001
CS-551, Lecture 2
49
Figure 2.10
Scheduling.
31 January 2001
Blind Concurrent
(Galli,p.48)
CS-551, Lecture 2
50
Remote procedure calls (RPC)
31 January 2001
CS-551, Lecture 2
51
Figure 3.9 Remote Procedure
Call Stubs. (Galli,p.73)
31 January 2001
CS-551, Lecture 2
52
Figure 3.10 Establishing
Communication for RPC.
(Galli,p.74)
31 January 2001
CS-551, Lecture 2
53