IIT
CS550
Techniques for Implementing
Quality of Service
in the Eclipse, Nemesis, and Real-Time Mach
Operating Systems
Francesca Ruffolo
December 6, 2001
Instructor: Dr. Marius Soneru
Comparative Operating Systems
December 2001
IIT
CS550
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Agenda
Motivation for Quality of Service
Implementation
Overview of Operating Systems
 Eclipse/BSD
 Nemesis
 Real Time Mach
Techniques for Implementing Quality of
Service
 Eclipse/BSD
 Nemesis
 Real Time Mach
Conclusion
References
Comparative Operating Systems
December 2001
IIT
CS550
Motivation for Quality of Service
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An increasing need to run multiple server
applications (audio and video media servers,
web servers and host services) for
organizations and individuals on the same
platform
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A need for control over provisioning of
system resources among applications to
achieve desired levels of predictable
performance
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Quality of service guarantees with respect to
packet delay and bandwidth are not extended
directly to the application via the operating
system and thus add little value
Comparative Operating Systems
December 2001
IIT
CS550
Operating System Overview
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Eclipse/BSD (Berkeley Software Distribution)
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Nemesis
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Real Time (RT) Mach
Comparative Operating Systems
December 2001
Overview of Eclipse/BSD
IIT
CS550
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Evolved from the Plan 9 operating system
developed by Bell Laboratories in New Jersey
starting in the late 1980’s in response to trends
in the computing industry at that time:
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Networks of smaller, more personal machines
were preferred over large centralized timeshared computers (typically UNIX
workstations)
Administrators grew weary of overloaded,
routine time-sharing systems and wished to
move to small, self-maintained systems
Referred to as Eclipse/BSD based off of FreeBSD
(Berkeley Software Distribution) version 3.4.
Comparative Operating Systems
December 2001
Overview of Nemesis
IIT
CS550
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Resulted from work completed for the
Pegasus and Pegasus II projects and the
following partnerships:
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University of Cambridge, U.K.
University of Twente, Netherlands
University of Glasgow, U.K.
Swedish Institute of Computer Science,
Sweden
Citrix Systems, LTD, U.K.
Runs on a large number of platforms
including Intel 486, Pentium, PPro, DEC Alpha
workstations, StrongARM SA-110 based
Comparative Operating Systems
network computers
December 2001
IIT
CS550
Overview of Real-Time Mach
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Research began in 1985 and resulted in a
flagship product developed by the Real-Time
and Multimedia Laboratory in partnership
with the Department of Computer Science at
Carnegie Mellon University.
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Incorporated into a number of commercial
operating systems including DEC’s OSF/1 for
the DEC Alpha and IBM-s OS/2 for the RS6000
based machines
Comparative Operating Systems
December 2001
IIT
CS550
Techniques for QoS Implementation
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Eclipse/BSD
 Reservations, Tagging, Reservation
Domains, Cumulative Service Guarantee,
Move-to-Rear List Scheduling (MTR-LS)
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Nemesis
 Quality of Service Manager, Run Time
Resource Allocation (RTRA), Accounting,
Policing
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Real-Time Mach
 Processor Reserves, Dynamic QoS Server,
QoS-based Resource Allocation Model (QRAM )
Comparative Operating Systems
December 2001
IIT
CS550
Eclipse/BSD – QoS Techniques
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Reservations
 /reserv (reservation) file system through which the
operating system can access, use and reconfigure
the system resource schedulers
 Each resource contains a reservation directory
(Example for CPU with multiple resources:
/reserv/CPU/r1, /reserv/CPU/r2, etc. )
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Quality of Service Parameters: Delay, Fairness, and
Cumulative Service Guarantee*
 Used to determine resource allocation to the
applications
 Obtains quality of service parameters and
compares the virtual service time to real service
time
Comparative Operating Systems
December 2001
Eclipse/BSD – QoS Techniques
IIT
CS550
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Reservation Domain
 Offers access and admissions to the /reserv file
system
 Allows control over system resources among
applications in order to achieve a desired
performance level
 Assigns a certain fraction of each resource: a
domain may contain 25% CPU, 50% disk I/O, 25%
main memory
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Move-to-Rear List Scheduling Algorithm
 Provides all three quality of service parameters:
bounded delay, cumulative guarantee, and fairness
 Contains an ordered list of pairs that indexes the
reservation domain and specifies the size of the
quantum or the maximum amount of service time
the reservation domain can receive without being
interrupted
Comparative Operating Systems
December 2001
IIT
CS550
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Nemesis - QoS Techniques
Quality of Service Manager
 Comes to agreement with processes about the quality of
service that will be delivered to them
 Receives a description of requirements from the
application and converts it to a set of QoS parameters
 Decides whether or not it can accommodate the request
 Informs the application directly if level of service
cannot be met (user is informed by QoS manager or
application)
 Informs application of resource availability if service
level can be met
Run time resource allocator (RTRA)
 Assigns the available resources among those applications
that need to use them by using QoS parameters supplied
by the QoS manager
 System dispatcher performs run time allocation in the case
of the processor resource
Comparative Operating Systems
December 2001
IIT
CS550
Nemesis - QoS Techniques
Q oS D escription
C ontract
Q oS M anager
A pplication
R esource
A llocatio n
P aram eters
R un T im e R esource A llocation
A cco unting
T im e
CPU
/
M em ory
Policing
….
I/O
F ig u re 2. Q o S M an ag em en t
Comparative Operating Systems
December 2001
IIT
CS550
Nemesis - QoS Techniques
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Policing
 Ensures that an application does not exceed its
allocation and start consuming resources reserved for
other applications (dispatcher monitors processor
time)
 Ensures that the writer of the application does not
request excessive resources to guarantee that
applications perform satisfactorily
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Accounting
 Kernals already account for resources used by an
application
 Cost of resources is charged to the accounting
structure that is associated with the currently executing
user mode protection domain (complicated because
the single client may need to interact with a number of
servers during execution)
 Credits or connection to a QoS server can be used to
resolve this issue
Comparative Operating Systems
December 2001
IIT
CS550
Real-Time Mach QoS Techniques
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Processor Reserves
 Allow threads to specify their CPU resource
requirements in terms of their timing constraints
 CPU demand is thus made available upon
admission of the processor reserve by the kernal
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Dynamic QoS Server
 Provides interaction between the application and
the system layer
 Application can specify its requirements to the
system layer while the system layer provides to the
application accurate and dynamic feedback on the
state of the applications resources both individually
and with respect to other applications
Comparative Operating Systems
December 2001
IIT
CS550
Real-Time Mach QoS Techniques
Client
QoS
Interface
Client
QoS
Interface
QoS Server
Display
Admission
Control
Dynamic
Quality Control
Client Quality
Attribute Database
Processor Reservation
Real- Time Mach
Figure 3. QoS Server Architecture
Comparative Operating Systems
December 2001
Real-Time Mach QoS Techniques
IIT
CS550
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QoS Based Resource Allocation Model (Q-RAM)
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Fulfills simultaneous requirements of multiple
applications along multiple QoS dimensions (e.g.
timeliness, data quality, reliable packet delivery)
while allowing applications access to multiple
resources (e.g CPU, disk bandwidth, memory)
simultaneously
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Takes
the
characteristics,
definitions
and
assumptions and makes resource allocations to
each application such that the total system utility is
maximized with the constraint that every
application is feasible with respect to each QoS
dimension
Comparative Operating Systems
December 2001
Conclusion
IIT
CS550
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All three systems use a mathematical model in
determining resource allocation to the applications
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Eclipse’s scheduling policy uses a cumulative
service guarantee, fairness and delay quality of
service parameters and compares the virtual
service time to real service time
Real-Time Mach uses the Q-RAM model where it
inputs its quality of service parameters to generate
utility functions that are then optimized
Nemesis utilizes the RTRA to assign the available
resources among applications using QoS
parameters supplied by the QoS manager
Comparative Operating Systems
December 2001
IIT
CS550
Conclusion
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Operating Systems used different methods of implementing
QoS
 Eclipse appears to add the mechanisms to support QoS
in the existing operating system
 Nemesis developed a separate module (QoS manager)
and provided links to integrate the module into the
system
 RT Mach implemented the majority of its changes in the
QoS server, a separate module, and integrated it to the
operating system with links limited to processor reserves
area of the operating system
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Disadvantages of integrating quality of service in an existing
system
 Possible drift from exact quality of service requirements
or objectives because altering was needed to fit the
quality of service mechanisms into the system
 Risk of inaccurately measuring the performance
 Risk of propagating effects through larger portions of the
system because the mechanisms added are at the lower
Comparative Operating Systems
levels of the operating system
December 2001
IIT
CS550
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Operating Systems with QoS Capability
Sumo (Lancaster University)
Synthesis (Columbia University)
Synthetix (Oregon Graduate Institute)
Vino (Harvard University)
Tornado (University of Toronto)
Scout (University of Arizona)
Comparative Operating Systems
December 2001
IIT
CS550
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Representative List of References
J. Blanquer, J. Bruno, E. Gabber, M. Mcshea, B. Özden, and A.
Silberschatz, "Resource Management for QoS Eclipse/BSD”
Proceedings of the FreeBSD 1999 Conference, Berkeley,
California,
October 1999.
J. Bruno, E. Gabber, B. Özden, and A. Silberschatz, "The Eclipse
Operating System: Providing Quality of Service via
Reservation Domains”. Proceedings of the USENIX 1998
Annual Technical Conference, New Orleans, Louisiana", June
1998.
E. Hyden. “Operating System Support for Quality of Service”.
Dissertation for degree of Doctor Of Philosophy. February,
1994, Chapters 3 and 4.
R. Rajkumar, C. Lee, J. Lehoczky and D. Siewiorek. "A Resource
Allocation Model for QoS Management" In Proceedings of
the IEEE
Real-Time Systems Symposium December, 1997.
See Report for remaining references
Comparative Operating Systems
December 2001