Ruffolo_Francesca_-_cs550_pres

8/8/2019 Ruffolo_Francesca_-_cs550_pres

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Comparative Operating SystemsDecember 2001

CS550

Techniques for ImplementingQuality of Service

in the Eclipse, Nemesis, and Real-Time MachOperating Systems

Francesca Ruffolo

December 6, 2001

Instructor: Dr. Marius Soneru


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CS550Agenda

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


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CS550Motivation for Quality of Service

An increasing need to run multiple server applications(audio and video media servers, web servers and hostservices) for organizations and individuals on the sameplatform

A need for control over provisioning of systemresources among applications to achieve desired levelsof predictable performance

Quality of service guarantees with respect to packetdelay and bandwidth are not extended directly to theapplication via the operating system and thus add littlevalue


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CS550Operating System Overview

Eclipse/BSD (Berkeley Software Distribution)

Nemesis

Real Time (RT) Mach


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CS550Overview of Eclipse/BSD

Evolved from the Plan 9 operating system developed byBell Laboratories in New Jersey starting in the late 1980sin response to trends in the computing industry at thattime:

Networks of smaller, more personal machines werepreferred over large centralized time-shared 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 (BerkeleySoftware Distribution) version 3.4.


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CS550Overview of Nemesis

Resulted from work completed for the Pegasus andPegasus II projects and the following partnerships:

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 Intel486, Pentium, PPro, DEC Alpha workstations,StrongARM SA-110 based network computers


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CS550Overview of Real-Time Mach

Research began in 1985 and resulted in a flagshipproduct developed by the Real-Time and MultimediaLaboratory in partnership with the Department of

Computer Science at Carnegie Mellon University.

Incorporated into a number of commercial operatingsystems including DECs OSF/1 for the DEC Alpha andIBM-s OS/2 for the RS6000 based machines


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CS550Techniques for QoS Implementation

Eclipse/BSD Reservations, Tagging, Reservation Domains,

Cumulative Service Guarantee, Move-to-Rear ListScheduling (MTR-LS)

Nemesis Quality of Service Manager, Run Time ResourceAllocation (RTRA), Accounting, Policing

Real-Time Mach Processor Reserves, Dynamic QoS Server, QoS-based Resource Allocation Model (Q-RAM )


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CS550Eclipse/BSD QoS Techniques

Reservations /reserv (reservation) file system through which the operating

system can access, use and reconfigure the system resourceschedulers

Each resource contains a reservation directory (Example for

CPU with multiple resources: /reserv/CPU/r1, /reserv/CPU/r2,etc. )

Quality of Service Parameters: Delay, Fairness, and CumulativeService Guarantee*

Used to determine resource allocation to the applications Obtains quality of service parameters and compares the virtual

service time to real service time


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CS550Eclipse/BSD QoS Techniques

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

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 maximumamount of service time the reservation domain can receivewithout being interrupted


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CS550Nemesis - 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 touse them by using QoS parameters supplied by the QoS manager

System dispatcher performs run time allocation in the case of theprocessor resource


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Time CPU Mem ory . I /O

Figure 2. QoS M anagement

Accounting / Polic in g

Run Time Resour ce A ll oca tion

A lica tionoS M ana er

Contr ac t

QoS Descrip tion

arameters ResourceA lloca tion


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Policing Ensures that an application does not exceed its allocation and startconsuming resources reserved for other applications (dispatchermonitors processor time)

Ensures that the writer of the application does not requestexcessive resources to guarantee that applications performsatisfactorily

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 interactwith a number of servers during execution) Credits or connection to a QoS server can be used to resolve this

issue


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CS550Real-Time Mach QoS Techniques

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

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 anddynamic feedback on the state of the applications resourcesboth individually and with respect to other applications


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Processor ReservationReal- Time Mach

QoS Server

Display

Admission DynamicControl Quality Control

Client Quality

Attribute Database

Client

QoS

Interface

Figure 3. QoS Server Architecture

Client

QoS

Interface


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QoS Based Resource Allocation Model (Q-RAM)

Fulfills simultaneous requirements of multiple applicationsalong 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

Takes the characteristics, definitions and assumptions andmakes resource allocations to each application such that thetotal system utility is maximized with the constraint that every

application is feasible with respect to each QoS dimension


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CS550Conclusion

All three systems use a mathematical model in determiningresource allocation to the applications

Eclipses scheduling policy uses a cumulative service

guarantee, fairness and delay quality of service parameters andcompares 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 thatare then optimized

Nemesis utilizes the RTRA to assign the available resources

among applications using QoS parameters supplied by theQoS manager


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CS550Conclusion

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 linkslimited to processor reserves area of the operating system

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 mechanismsinto 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 levels of theoperating system


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CS550Operating Systems with QoS Capability

Sumo (Lancaster University)

Synthesis (Columbia University) Synthetix (Oregon Graduate Institute)

Vino (Harvard University)

Tornado (University of Toronto)

Scout (University ofArizona)


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CS550Representative List of References

J. Blanquer, J. Bruno, E. Gabber, M. Mcshea, B. zden, and A.

Silberschatz, "Resource Management for QoS Eclipse/BSDProceedings of the FreeBSD 1999 Conference, Berkeley, California,October 1999.

J. Bruno, E. Gabber, B. zden, and A. Silberschatz, "The EclipseOperating System: Providing Quality of Service via

Reservation Domains. Proceedings of the USENIX 1998Annual Technical Conference, New Orleans, Louisiana", June1998.

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 AllocationModel for QoS Management" In Proceedings of the IEEE Real-Time SystemsSymposium December, 1997.

See Report for remaining references

Ruffolo_Francesca_-_cs550_pres

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